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  /**
   * Backbone-relational.js 0.9.0
   * (c) 2011-2014 Paul Uithol and contributors (https://github.com/PaulUithol/Backbone-relational/graphs/contributors)
   *
   * Backbone-relational may be freely distributed under the MIT license; see the accompanying LICENSE.txt.
   * For details and documentation: https://github.com/PaulUithol/Backbone-relational.
   * Depends on Backbone (and thus on Underscore as well): https://github.com/documentcloud/backbone.
   *
   * Example:
   *
      Zoo = Backbone.RelationalModel.extend({
          relations: [ {
              type: Backbone.HasMany,
              key: 'animals',
              relatedModel: 'Animal',
              reverseRelation: {
                  key: 'livesIn',
                  includeInJSON: 'id'
                  // 'relatedModel' is automatically set to 'Zoo'; the 'relationType' to 'HasOne'.
              }
          } ],
  
          toString: function() {
              return this.get( 'name' );
          }
      });
  
      Animal = Backbone.RelationalModel.extend({
          toString: function() {
              return this.get( 'species' );
          }
      });
  
      // Creating the zoo will give it a collection with one animal in it: the monkey.
      // The animal created after that has a relation `livesIn` that points to the zoo it's currently associated with.
      // If you instantiate (or fetch) the zebra later, it will automatically be added.
  
      var zoo = new Zoo({
          name: 'Artis',
          animals: [ { id: 'monkey-1', species: 'Chimp' }, 'lion-1', 'zebra-1' ]
      });
  
      var lion = new Animal( { id: 'lion-1', species: 'Lion' } ),
          monkey = zoo.get( 'animals' ).first(),
          sameZoo = lion.get( 'livesIn' );
   */
  ( function( root, factory ) {
      // Set up Backbone-relational for the environment. Start with AMD.
      if ( typeof define === 'function' && define.amd ) {
          define( [ 'exports', 'backbone', 'underscore' ], factory );
      }
      // Next for Node.js or CommonJS.
      else if ( typeof exports !== 'undefined' ) {
          factory( exports, require( 'backbone' ), require( 'underscore' ) );
      }
      // Finally, as a browser global. Use `root` here as it references `window`.
      else {
          factory( root, root.Backbone, root._ );
      }
  }( this, function( exports, Backbone, _ ) {
      "use strict";
  
      Backbone.Relational = {
          showWarnings: true
      };
  
      /**
       * Semaphore mixin; can be used as both binary and counting.
       **/
      Backbone.Semaphore = {
          _permitsAvailable: null,
          _permitsUsed: 0,
  
          acquire: function() {
              if ( this._permitsAvailable && this._permitsUsed >= this._permitsAvailable ) {
                  throw new Error( 'Max permits acquired' );
              }
              else {
                  this._permitsUsed++;
              }
          },
  
          release: function() {
              if ( this._permitsUsed === 0 ) {
                  throw new Error( 'All permits released' );
              }
              else {
                  this._permitsUsed--;
              }
          },
  
          isLocked: function() {
              return this._permitsUsed > 0;
          },
  
          setAvailablePermits: function( amount ) {
              if ( this._permitsUsed > amount ) {
                  throw new Error( 'Available permits cannot be less than used permits' );
              }
              this._permitsAvailable = amount;
          }
      };
  
      /**
       * A BlockingQueue that accumulates items while blocked (via 'block'),
       * and processes them when unblocked (via 'unblock').
       * Process can also be called manually (via 'process').
       */
      Backbone.BlockingQueue = function() {
          this._queue = [];
      };
      _.extend( Backbone.BlockingQueue.prototype, Backbone.Semaphore, {
          _queue: null,
  
          add: function( func ) {
              if ( this.isBlocked() ) {
                  this._queue.push( func );
              }
              else {
                  func();
              }
          },
  
          // Some of the queued events may trigger other blocking events. By
          // copying the queue here it allows queued events to process closer to
          // the natural order.
          //
          // queue events [ 'A', 'B', 'C' ]
          // A handler of 'B' triggers 'D' and 'E'
          // By copying `this._queue` this executes:
          // [ 'A', 'B', 'D', 'E', 'C' ]
          // The same order the would have executed if they didn't have to be
          // delayed and queued.
          process: function() {
              var queue = this._queue;
              this._queue = [];
              while ( queue && queue.length ) {
                  queue.shift()();
              }
          },
  
          block: function() {
              this.acquire();
          },
  
          unblock: function() {
              this.release();
              if ( !this.isBlocked() ) {
                  this.process();
              }
          },
  
          isBlocked: function() {
              return this.isLocked();
          }
      });
      /**
       * Global event queue. Accumulates external events ('add:<key>', 'remove:<key>' and 'change:<key>')
       * until the top-level object is fully initialized (see 'Backbone.RelationalModel').
       */
      Backbone.Relational.eventQueue = new Backbone.BlockingQueue();
  
      /**
       * Backbone.Store keeps track of all created (and destruction of) Backbone.RelationalModel.
       * Handles lookup for relations.
       */
      Backbone.Store = function() {
          this._collections = [];
          this._reverseRelations = [];
          this._orphanRelations = [];
          this._subModels = [];
          this._modelScopes = [ exports ];
      };
      _.extend( Backbone.Store.prototype, Backbone.Events, {
          /**
           * Create a new `Relation`.
           * @param {Backbone.RelationalModel} [model]
           * @param {Object} relation
           * @param {Object} [options]
           */
          initializeRelation: function( model, relation, options ) {
              var type = !_.isString( relation.type ) ? relation.type : Backbone[ relation.type ] || this.getObjectByName( relation.type );
              if ( type && type.prototype instanceof Backbone.Relation ) {
                  var rel = new type( model, relation, options ); // Also pushes the new Relation into `model._relations`
              }
              else {
                  Backbone.Relational.showWarnings && typeof console !== 'undefined' && console.warn( 'Relation=%o; missing or invalid relation type!', relation );
              }
          },
  
          /**
           * Add a scope for `getObjectByName` to look for model types by name.
           * @param {Object} scope
           */
          addModelScope: function( scope ) {
              this._modelScopes.push( scope );
          },
  
          /**
           * Remove a scope.
           * @param {Object} scope
           */
          removeModelScope: function( scope ) {
              this._modelScopes = _.without( this._modelScopes, scope );
          },
  
          /**
           * Add a set of subModelTypes to the store, that can be used to resolve the '_superModel'
           * for a model later in 'setupSuperModel'.
           *
           * @param {Backbone.RelationalModel} subModelTypes
           * @param {Backbone.RelationalModel} superModelType
           */
          addSubModels: function( subModelTypes, superModelType ) {
              this._subModels.push({
                  'superModelType': superModelType,
                  'subModels': subModelTypes
              });
          },
  
          /**
           * Check if the given modelType is registered as another model's subModel. If so, add it to the super model's
           * '_subModels', and set the modelType's '_superModel', '_subModelTypeName', and '_subModelTypeAttribute'.
           *
           * @param {Backbone.RelationalModel} modelType
           */
          setupSuperModel: function( modelType ) {
              _.find( this._subModels, function( subModelDef ) {
                  return _.filter( subModelDef.subModels || [], function( subModelTypeName, typeValue ) {
                      var subModelType = this.getObjectByName( subModelTypeName );
  
                      if ( modelType === subModelType ) {
                          // Set 'modelType' as a child of the found superModel
                          subModelDef.superModelType._subModels[ typeValue ] = modelType;
  
                          // Set '_superModel', '_subModelTypeValue', and '_subModelTypeAttribute' on 'modelType'.
                          modelType._superModel = subModelDef.superModelType;
                          modelType._subModelTypeValue = typeValue;
                          modelType._subModelTypeAttribute = subModelDef.superModelType.prototype.subModelTypeAttribute;
                          return true;
                      }
                  }, this ).length;
              }, this );
          },
  
          /**
           * Add a reverse relation. Is added to the 'relations' property on model's prototype, and to
           * existing instances of 'model' in the store as well.
           * @param {Object} relation
           * @param {Backbone.RelationalModel} relation.model
           * @param {String} relation.type
           * @param {String} relation.key
           * @param {String|Object} relation.relatedModel
           */
          addReverseRelation: function( relation ) {
              var exists = _.any( this._reverseRelations, function( rel ) {
                  return _.all( relation || [], function( val, key ) {
                      return val === rel[ key ];
                  });
              });
  
              if ( !exists && relation.model && relation.type ) {
                  this._reverseRelations.push( relation );
                  this._addRelation( relation.model, relation );
                  this.retroFitRelation( relation );
              }
          },
  
          /**
           * Deposit a `relation` for which the `relatedModel` can't be resolved at the moment.
           *
           * @param {Object} relation
           */
          addOrphanRelation: function( relation ) {
              var exists = _.any( this._orphanRelations, function( rel ) {
                  return _.all( relation || [], function( val, key ) {
                      return val === rel[ key ];
                  });
              });
  
              if ( !exists && relation.model && relation.type ) {
                  this._orphanRelations.push( relation );
              }
          },
  
          /**
           * Try to initialize any `_orphanRelation`s
           */
          processOrphanRelations: function() {
              // Make sure to operate on a copy since we're removing while iterating
              _.each( this._orphanRelations.slice( 0 ), function( rel ) {
                  var relatedModel = Backbone.Relational.store.getObjectByName( rel.relatedModel );
                  if ( relatedModel ) {
                      this.initializeRelation( null, rel );
                      this._orphanRelations = _.without( this._orphanRelations, rel );
                  }
              }, this );
          },
  
          /**
           *
           * @param {Backbone.RelationalModel.constructor} type
           * @param {Object} relation
           * @private
           */
          _addRelation: function( type, relation ) {
              if ( !type.prototype.relations ) {
                  type.prototype.relations = [];
              }
              type.prototype.relations.push( relation );
  
              _.each( type._subModels || [], function( subModel ) {
                  this._addRelation( subModel, relation );
              }, this );
          },
  
          /**
           * Add a 'relation' to all existing instances of 'relation.model' in the store
           * @param {Object} relation
           */
          retroFitRelation: function( relation ) {
              var coll = this.getCollection( relation.model, false );
              coll && coll.each( function( model ) {
                  if ( !( model instanceof relation.model ) ) {
                      return;
                  }
  
                  var rel = new relation.type( model, relation );
              }, this );
          },
  
          /**
           * Find the Store's collection for a certain type of model.
           * @param {Backbone.RelationalModel} type
           * @param {Boolean} [create=true] Should a collection be created if none is found?
           * @return {Backbone.Collection} A collection if found (or applicable for 'model'), or null
           */
          getCollection: function( type, create ) {
              if ( type instanceof Backbone.RelationalModel ) {
                  type = type.constructor;
              }
  
              var rootModel = type;
              while ( rootModel._superModel ) {
                  rootModel = rootModel._superModel;
              }
  
              var coll = _.find( this._collections, function( item ) {
                  return item.model === rootModel;
              });
  
              if ( !coll && create !== false ) {
                  coll = this._createCollection( rootModel );
              }
  
              return coll;
          },
  
          /**
           * Find a model type on one of the modelScopes by name. Names are split on dots.
           * @param {String} name
           * @return {Object}
           */
          getObjectByName: function( name ) {
              var parts = name.split( '.' ),
                  type = null;
  
              _.find( this._modelScopes, function( scope ) {
                  type = _.reduce( parts || [], function( memo, val ) {
                      return memo ? memo[ val ] : undefined;
                  }, scope );
  
                  if ( type && type !== scope ) {
                      return true;
                  }
              }, this );
  
              return type;
          },
  
          _createCollection: function( type ) {
              var coll;
  
              // If 'type' is an instance, take its constructor
              if ( type instanceof Backbone.RelationalModel ) {
                  type = type.constructor;
              }
  
              // Type should inherit from Backbone.RelationalModel.
              if ( type.prototype instanceof Backbone.RelationalModel ) {
                  coll = new Backbone.Collection();
                  coll.model = type;
  
                  this._collections.push( coll );
              }
  
              return coll;
          },
  
          /**
           * Find the attribute that is to be used as the `id` on a given object
           * @param type
           * @param {String|Number|Object|Backbone.RelationalModel} item
           * @return {String|Number}
           */
          resolveIdForItem: function( type, item ) {
              var id = _.isString( item ) || _.isNumber( item ) ? item : null;
  
              if ( id === null ) {
                  if ( item instanceof Backbone.RelationalModel ) {
                      id = item.id;
                  }
                  else if ( _.isObject( item ) ) {
                      id = item[ type.prototype.idAttribute ];
                  }
              }
  
              // Make all falsy values `null` (except for 0, which could be an id.. see '/issues/179')
              if ( !id && id !== 0 ) {
                  id = null;
              }
  
              return id;
          },
  
          /**
           * Find a specific model of a certain `type` in the store
           * @param type
           * @param {String|Number|Object|Backbone.RelationalModel} item
           */
          find: function( type, item ) {
              var id = this.resolveIdForItem( type, item ),
                  coll = this.getCollection( type );
  
              // Because the found object could be of any of the type's superModel
              // types, only return it if it's actually of the type asked for.
              if ( coll ) {
                  var obj = coll.get( id );
  
                  if ( obj instanceof type ) {
                      return obj;
                  }
              }
  
              return null;
          },
  
          /**
           * Add a 'model' to its appropriate collection. Retain the original contents of 'model.collection'.
           * @param {Backbone.RelationalModel} model
           */
          register: function( model ) {
              var coll = this.getCollection( model );
  
              if ( coll ) {
                  var modelColl = model.collection;
                  coll.add( model );
                  model.collection = modelColl;
              }
          },
  
          /**
           * Check if the given model may use the given `id`
           * @param model
           * @param [id]
           */
          checkId: function( model, id ) {
              var coll = this.getCollection( model ),
                  duplicate = coll && coll.get( id );
  
              if ( duplicate && model !== duplicate ) {
                  if ( Backbone.Relational.showWarnings && typeof console !== 'undefined' ) {
                      console.warn( 'Duplicate id! Old RelationalModel=%o, new RelationalModel=%o', duplicate, model );
                  }
  
                  throw new Error( "Cannot instantiate more than one Backbone.RelationalModel with the same id per type!" );
              }
          },
  
          /**
           * Explicitly update a model's id in its store collection
           * @param {Backbone.RelationalModel} model
           */
          update: function( model ) {
              var coll = this.getCollection( model );
  
              // Register a model if it isn't yet (which happens if it was created without an id).
              if ( !coll.contains( model ) ) {
                  this.register( model );
              }
  
              // This triggers updating the lookup indices kept in a collection
              coll._onModelEvent( 'change:' + model.idAttribute, model, coll );
  
              // Trigger an event on model so related models (having the model's new id in their keyContents) can add it.
              model.trigger( 'relational:change:id', model, coll );
          },
  
          /**
           * Unregister from the store: a specific model, a collection, or a model type.
           * @param {Backbone.RelationalModel|Backbone.RelationalModel.constructor|Backbone.Collection} type
           */
          unregister: function( type ) {
              var coll,
                  models;
  
              if ( type instanceof Backbone.Model ) {
                  coll = this.getCollection( type );
                  models = [ type ];
              }
              else if ( type instanceof Backbone.Collection ) {
                  coll = this.getCollection( type.model );
                  models = _.clone( type.models );
              }
              else {
                  coll = this.getCollection( type );
                  models = _.clone( coll.models );
              }
  
              _.each( models, function( model ) {
                  this.stopListening( model );
                  _.invoke( model.getRelations(), 'stopListening' );
              }, this );
  
  
              // If we've unregistered an entire store collection, reset the collection (which is much faster).
              // Otherwise, remove each model one by one.
              if ( _.contains( this._collections, type ) ) {
                  coll.reset( [] );
              }
              else {
                  _.each( models, function( model ) {
                      if ( coll.get( model ) ) {
                          coll.remove( model );
                      }
                      else {
                          coll.trigger( 'relational:remove', model, coll );
                      }
                  }, this );
              }
          },
  
          /**
           * Reset the `store` to it's original state. The `reverseRelations` are kept though, since attempting to
           * re-initialize these on models would lead to a large amount of warnings.
           */
          reset: function() {
              this.stopListening();
  
              // Unregister each collection to remove event listeners
              _.each( this._collections, function( coll ) {
                  this.unregister( coll );
              }, this );
  
              this._collections = [];
              this._subModels = [];
              this._modelScopes = [ exports ];
          }
      });
      Backbone.Relational.store = new Backbone.Store();
  
      /**
       * The main Relation class, from which 'HasOne' and 'HasMany' inherit. Internally, 'relational:<key>' events
       * are used to regulate addition and removal of models from relations.
       *
       * @param {Backbone.RelationalModel} [instance] Model that this relation is created for. If no model is supplied,
       *      Relation just tries to instantiate it's `reverseRelation` if specified, and bails out after that.
       * @param {Object} options
       * @param {string} options.key
       * @param {Backbone.RelationalModel.constructor} options.relatedModel
       * @param {Boolean|String} [options.includeInJSON=true] Serialize the given attribute for related model(s)' in toJSON, or just their ids.
       * @param {Boolean} [options.createModels=true] Create objects from the contents of keys if the object is not found in Backbone.store.
       * @param {Object} [options.reverseRelation] Specify a bi-directional relation. If provided, Relation will reciprocate
       *    the relation to the 'relatedModel'. Required and optional properties match 'options', except that it also needs
       *    {Backbone.Relation|String} type ('HasOne' or 'HasMany').
       * @param {Object} opts
       */
      Backbone.Relation = function( instance, options, opts ) {
          this.instance = instance;
          // Make sure 'options' is sane, and fill with defaults from subclasses and this object's prototype
          options = _.isObject( options ) ? options : {};
          this.reverseRelation = _.defaults( options.reverseRelation || {}, this.options.reverseRelation );
          this.options = _.defaults( options, this.options, Backbone.Relation.prototype.options );
  
          this.reverseRelation.type = !_.isString( this.reverseRelation.type ) ? this.reverseRelation.type :
              Backbone[ this.reverseRelation.type ] || Backbone.Relational.store.getObjectByName( this.reverseRelation.type );
  
          this.key = this.options.key;
          this.keySource = this.options.keySource || this.key;
          this.keyDestination = this.options.keyDestination || this.keySource || this.key;
  
          this.model = this.options.model || this.instance.constructor;
  
          this.relatedModel = this.options.relatedModel;
  
          // No 'relatedModel' is interpreted as self-referential
          if ( _.isUndefined( this.relatedModel ) ) {
              this.relatedModel = this.model;
          }
  
          // Otherwise, try to resolve the given value to an object
          if ( _.isFunction( this.relatedModel ) && !( this.relatedModel.prototype instanceof Backbone.RelationalModel ) ) {
              this.relatedModel = _.result( this, 'relatedModel' );
          }
          if ( _.isString( this.relatedModel ) ) {
              this.relatedModel = Backbone.Relational.store.getObjectByName( this.relatedModel );
          }
  
  
          if ( !this.checkPreconditions() ) {
              return;
          }
  
          // Add the reverse relation on 'relatedModel' to the store's reverseRelations
          if ( !this.options.isAutoRelation && this.reverseRelation.type && this.reverseRelation.key ) {
              Backbone.Relational.store.addReverseRelation( _.defaults( {
                      isAutoRelation: true,
                      model: this.relatedModel,
                      relatedModel: this.model,
                      reverseRelation: this.options // current relation is the 'reverseRelation' for its own reverseRelation
                  },
                  this.reverseRelation // Take further properties from this.reverseRelation (type, key, etc.)
              ) );
          }
  
          if ( instance ) {
              var contentKey = this.keySource;
              if ( contentKey !== this.key && _.isObject( this.instance.get( this.key ) ) ) {
                  contentKey = this.key;
              }
  
              this.setKeyContents( this.instance.get( contentKey ) );
              this.relatedCollection = Backbone.Relational.store.getCollection( this.relatedModel );
  
              // Explicitly clear 'keySource', to prevent a leaky abstraction if 'keySource' differs from 'key'.
              if ( this.keySource !== this.key ) {
                  delete this.instance.attributes[ this.keySource ];
              }
  
              // Add this Relation to instance._relations
              this.instance._relations[ this.key ] = this;
  
              this.initialize( opts );
  
              if ( this.options.autoFetch ) {
                  this.instance.getAsync( this.key, _.isObject( this.options.autoFetch ) ? this.options.autoFetch : {} );
              }
  
              // When 'relatedModel' are created or destroyed, check if it affects this relation.
              this.listenTo( this.instance, 'destroy', this.destroy )
                  .listenTo( this.relatedCollection, 'relational:add relational:change:id', this.tryAddRelated )
                  .listenTo( this.relatedCollection, 'relational:remove', this.removeRelated );
          }
      };
      // Fix inheritance :\
      Backbone.Relation.extend = Backbone.Model.extend;
      // Set up all inheritable **Backbone.Relation** properties and methods.
      _.extend( Backbone.Relation.prototype, Backbone.Events, Backbone.Semaphore, {
          options: {
              createModels: true,
              includeInJSON: true,
              isAutoRelation: false,
              autoFetch: false,
              parse: false
          },
  
          instance: null,
          key: null,
          keyContents: null,
          relatedModel: null,
          relatedCollection: null,
          reverseRelation: null,
          related: null,
  
          /**
           * Check several pre-conditions.
           * @return {Boolean} True if pre-conditions are satisfied, false if they're not.
           */
          checkPreconditions: function() {
              var i = this.instance,
                  k = this.key,
                  m = this.model,
                  rm = this.relatedModel,
                  warn = Backbone.Relational.showWarnings && typeof console !== 'undefined';
  
              if ( !m || !k || !rm ) {
                  warn && console.warn( 'Relation=%o: missing model, key or relatedModel (%o, %o, %o).', this, m, k, rm );
                  return false;
              }
              // Check if the type in 'model' inherits from Backbone.RelationalModel
              if ( !( m.prototype instanceof Backbone.RelationalModel ) ) {
                  warn && console.warn( 'Relation=%o: model does not inherit from Backbone.RelationalModel (%o).', this, i );
                  return false;
              }
              // Check if the type in 'relatedModel' inherits from Backbone.RelationalModel
              if ( !( rm.prototype instanceof Backbone.RelationalModel ) ) {
                  warn && console.warn( 'Relation=%o: relatedModel does not inherit from Backbone.RelationalModel (%o).', this, rm );
                  return false;
              }
              // Check if this is not a HasMany, and the reverse relation is HasMany as well
              if ( this instanceof Backbone.HasMany && this.reverseRelation.type === Backbone.HasMany ) {
                  warn && console.warn( 'Relation=%o: relation is a HasMany, and the reverseRelation is HasMany as well.', this );
                  return false;
              }
              // Check if we're not attempting to create a relationship on a `key` that's already used.
              if ( i && _.keys( i._relations ).length ) {
                  var existing = _.find( i._relations, function( rel ) {
                      return rel.key === k;
                  }, this );
  
                  if ( existing ) {
                      warn && console.warn( 'Cannot create relation=%o on %o for model=%o: already taken by relation=%o.',
                          this, k, i, existing );
                      return false;
                  }
              }
  
              return true;
          },
  
          /**
           * Set the related model(s) for this relation
           * @param {Backbone.Model|Backbone.Collection} related
           */
          setRelated: function( related ) {
              this.related = related;
              this.instance.attributes[ this.key ] = related;
          },
  
          /**
           * Determine if a relation (on a different RelationalModel) is the reverse
           * relation of the current one.
           * @param {Backbone.Relation} relation
           * @return {Boolean}
           */
          _isReverseRelation: function( relation ) {
              return relation.instance instanceof this.relatedModel && this.reverseRelation.key === relation.key &&
                  this.key === relation.reverseRelation.key;
          },
  
          /**
           * Get the reverse relations (pointing back to 'this.key' on 'this.instance') for the currently related model(s).
           * @param {Backbone.RelationalModel} [model] Get the reverse relations for a specific model.
           *    If not specified, 'this.related' is used.
           * @return {Backbone.Relation[]}
           */
          getReverseRelations: function( model ) {
              var reverseRelations = [];
              // Iterate over 'model', 'this.related.models' (if this.related is a Backbone.Collection), or wrap 'this.related' in an array.
              var models = !_.isUndefined( model ) ? [ model ] : this.related && ( this.related.models || [ this.related ] ),
                  relations = null,
                  relation = null;
  
              for( var i = 0; i < ( models || [] ).length; i++ ) {
                  relations = models[ i ].getRelations() || [];
  
                  for( var j = 0; j < relations.length; j++ ) {
                      relation = relations[ j ];
  
                      if ( this._isReverseRelation( relation ) ) {
                          reverseRelations.push( relation );
                      }
                  }
              }
  
              return reverseRelations;
          },
  
          /**
           * When `this.instance` is destroyed, cleanup our relations.
           * Get reverse relation, call removeRelated on each.
           */
          destroy: function() {
              this.stopListening();
  
              if ( this instanceof Backbone.HasOne ) {
                  this.setRelated( null );
              }
              else if ( this instanceof Backbone.HasMany ) {
                  this.setRelated( this._prepareCollection() );
              }
  
              _.each( this.getReverseRelations(), function( relation ) {
                  relation.removeRelated( this.instance );
              }, this );
          }
      });
  
      Backbone.HasOne = Backbone.Relation.extend({
          options: {
              reverseRelation: { type: 'HasMany' }
          },
  
          initialize: function( opts ) {
              this.listenTo( this.instance, 'relational:change:' + this.key, this.onChange );
  
              var related = this.findRelated( opts );
              this.setRelated( related );
  
              // Notify new 'related' object of the new relation.
              _.each( this.getReverseRelations(), function( relation ) {
                  relation.addRelated( this.instance, opts );
              }, this );
          },
  
          /**
           * Find related Models.
           * @param {Object} [options]
           * @return {Backbone.Model}
           */
          findRelated: function( options ) {
              var related = null;
  
              options = _.defaults( { parse: this.options.parse }, options );
  
              if ( this.keyContents instanceof this.relatedModel ) {
                  related = this.keyContents;
              }
              else if ( this.keyContents || this.keyContents === 0 ) { // since 0 can be a valid `id` as well
                  var opts = _.defaults( { create: this.options.createModels }, options );
                  related = this.relatedModel.findOrCreate( this.keyContents, opts );
              }
  
              // Nullify `keyId` if we have a related model; in case it was already part of the relation
              if ( related ) {
                  this.keyId = null;
              }
  
              return related;
          },
  
          /**
           * Normalize and reduce `keyContents` to an `id`, for easier comparison
           * @param {String|Number|Backbone.Model} keyContents
           */
          setKeyContents: function( keyContents ) {
              this.keyContents = keyContents;
              this.keyId = Backbone.Relational.store.resolveIdForItem( this.relatedModel, this.keyContents );
          },
  
          /**
           * Event handler for `change:<key>`.
           * If the key is changed, notify old & new reverse relations and initialize the new relation.
           */
          onChange: function( model, attr, options ) {
              // Don't accept recursive calls to onChange (like onChange->findRelated->findOrCreate->initializeRelations->addRelated->onChange)
              if ( this.isLocked() ) {
                  return;
              }
              this.acquire();
              options = options ? _.clone( options ) : {};
  
              // 'options.__related' is set by 'addRelated'/'removeRelated'. If it is set, the change
              // is the result of a call from a relation. If it's not, the change is the result of
              // a 'set' call on this.instance.
              var changed = _.isUndefined( options.__related ),
                  oldRelated = changed ? this.related : options.__related;
  
              if ( changed ) {
                  this.setKeyContents( attr );
                  var related = this.findRelated( options );
                  this.setRelated( related );
              }
  
              // Notify old 'related' object of the terminated relation
              if ( oldRelated && this.related !== oldRelated ) {
                  _.each( this.getReverseRelations( oldRelated ), function( relation ) {
                      relation.removeRelated( this.instance, null, options );
                  }, this );
              }
  
              // Notify new 'related' object of the new relation. Note we do re-apply even if this.related is oldRelated;
              // that can be necessary for bi-directional relations if 'this.instance' was created after 'this.related'.
              // In that case, 'this.instance' will already know 'this.related', but the reverse might not exist yet.
              _.each( this.getReverseRelations(), function( relation ) {
                  relation.addRelated( this.instance, options );
              }, this );
  
              // Fire the 'change:<key>' event if 'related' was updated
              if ( !options.silent && this.related !== oldRelated ) {
                  var dit = this;
                  this.changed = true;
                  Backbone.Relational.eventQueue.add( function() {
                      dit.instance.trigger( 'change:' + dit.key, dit.instance, dit.related, options, true );
                      dit.changed = false;
                  });
              }
              this.release();
          },
  
          /**
           * If a new 'this.relatedModel' appears in the 'store', try to match it to the last set 'keyContents'
           */
          tryAddRelated: function( model, coll, options ) {
              if ( ( this.keyId || this.keyId === 0 ) && model.id === this.keyId ) { // since 0 can be a valid `id` as well
                  this.addRelated( model, options );
                  this.keyId = null;
              }
          },
  
          addRelated: function( model, options ) {
              // Allow 'model' to set up its relations before proceeding.
              // (which can result in a call to 'addRelated' from a relation of 'model')
              var dit = this;
              model.queue( function() {
                  if ( model !== dit.related ) {
                      var oldRelated = dit.related || null;
                      dit.setRelated( model );
                      dit.onChange( dit.instance, model, _.defaults( { __related: oldRelated }, options ) );
                  }
              });
          },
  
          removeRelated: function( model, coll, options ) {
              if ( !this.related ) {
                  return;
              }
  
              if ( model === this.related ) {
                  var oldRelated = this.related || null;
                  this.setRelated( null );
                  this.onChange( this.instance, model, _.defaults( { __related: oldRelated }, options ) );
              }
          }
      });
  
      Backbone.HasMany = Backbone.Relation.extend({
          collectionType: null,
  
          options: {
              reverseRelation: { type: 'HasOne' },
              collectionType: Backbone.Collection,
              collectionKey: true,
              collectionOptions: {}
          },
  
          initialize: function( opts ) {
              this.listenTo( this.instance, 'relational:change:' + this.key, this.onChange );
  
              // Handle a custom 'collectionType'
              this.collectionType = this.options.collectionType;
              if ( _.isFunction( this.collectionType ) && this.collectionType !== Backbone.Collection && !( this.collectionType.prototype instanceof Backbone.Collection ) ) {
                  this.collectionType = _.result( this, 'collectionType' );
              }
              if ( _.isString( this.collectionType ) ) {
                  this.collectionType = Backbone.Relational.store.getObjectByName( this.collectionType );
              }
              if ( this.collectionType !== Backbone.Collection && !( this.collectionType.prototype instanceof Backbone.Collection ) ) {
                  throw new Error( '`collectionType` must inherit from Backbone.Collection' );
              }
  
              var related = this.findRelated( opts );
              this.setRelated( related );
          },
  
          /**
           * Bind events and setup collectionKeys for a collection that is to be used as the backing store for a HasMany.
           * If no 'collection' is supplied, a new collection will be created of the specified 'collectionType' option.
           * @param {Backbone.Collection} [collection]
           * @return {Backbone.Collection}
           */
          _prepareCollection: function( collection ) {
              if ( this.related ) {
                  this.stopListening( this.related );
              }
  
              if ( !collection || !( collection instanceof Backbone.Collection ) ) {
                  var options = _.isFunction( this.options.collectionOptions ) ?
                      this.options.collectionOptions( this.instance ) : this.options.collectionOptions;
  
                  collection = new this.collectionType( null, options );
              }
  
              collection.model = this.relatedModel;
  
              if ( this.options.collectionKey ) {
                  var key = this.options.collectionKey === true ? this.options.reverseRelation.key : this.options.collectionKey;
  
                  if ( collection[ key ] && collection[ key ] !== this.instance ) {
                      if ( Backbone.Relational.showWarnings && typeof console !== 'undefined' ) {
                          console.warn( 'Relation=%o; collectionKey=%s already exists on collection=%o', this, key, this.options.collectionKey );
                      }
                  }
                  else if ( key ) {
                      collection[ key ] = this.instance;
                  }
              }
  
              this.listenTo( collection, 'relational:add', this.handleAddition )
                  .listenTo( collection, 'relational:remove', this.handleRemoval )
                  .listenTo( collection, 'relational:reset', this.handleReset );
  
              return collection;
          },
  
          /**
           * Find related Models.
           * @param {Object} [options]
           * @return {Backbone.Collection}
           */
          findRelated: function( options ) {
              var related = null;
  
              options = _.defaults( { parse: this.options.parse }, options );
  
              // Replace 'this.related' by 'this.keyContents' if it is a Backbone.Collection
              if ( this.keyContents instanceof Backbone.Collection ) {
                  this._prepareCollection( this.keyContents );
                  related = this.keyContents;
              }
              // Otherwise, 'this.keyContents' should be an array of related object ids.
              // Re-use the current 'this.related' if it is a Backbone.Collection; otherwise, create a new collection.
              else {
                  var toAdd = [];
  
                  _.each( this.keyContents, function( attributes ) {
                      var model = null;
  
                      if ( attributes instanceof this.relatedModel ) {
                          model = attributes;
                      }
                      else {
                          // If `merge` is true, update models here, instead of during update.
                          model = this.relatedModel.findOrCreate( attributes,
                              _.extend( { merge: true }, options, { create: this.options.createModels } )
                          );
                      }
  
                      model && toAdd.push( model );
                  }, this );
  
                  if ( this.related instanceof Backbone.Collection ) {
                      related = this.related;
                  }
                  else {
                      related = this._prepareCollection();
                  }
  
                  // By now, both `merge` and `parse` will already have been executed for models if they were specified.
                  // Disable them to prevent additional calls.
                  related.set( toAdd, _.defaults( { merge: false, parse: false }, options ) );
              }
  
              // Remove entries from `keyIds` that were already part of the relation (and are thus 'unchanged')
              this.keyIds = _.difference( this.keyIds, _.pluck( related.models, 'id' ) );
  
              return related;
          },
  
          /**
           * Normalize and reduce `keyContents` to a list of `ids`, for easier comparison
           * @param {String|Number|String[]|Number[]|Backbone.Collection} keyContents
           */
          setKeyContents: function( keyContents ) {
              this.keyContents = keyContents instanceof Backbone.Collection ? keyContents : null;
              this.keyIds = [];
  
              if ( !this.keyContents && ( keyContents || keyContents === 0 ) ) { // since 0 can be a valid `id` as well
                  // Handle cases the an API/user supplies just an Object/id instead of an Array
                  this.keyContents = _.isArray( keyContents ) ? keyContents : [ keyContents ];
  
                  _.each( this.keyContents, function( item ) {
                      var itemId = Backbone.Relational.store.resolveIdForItem( this.relatedModel, item );
                      if ( itemId || itemId === 0 ) {
                          this.keyIds.push( itemId );
                      }
                  }, this );
              }
          },
  
          /**
           * Event handler for `change:<key>`.
           * If the contents of the key are changed, notify old & new reverse relations and initialize the new relation.
           */
          onChange: function( model, attr, options ) {
              options = options ? _.clone( options ) : {};
              this.setKeyContents( attr );
              this.changed = false;
  
              var related = this.findRelated( options );
              this.setRelated( related );
  
              if ( !options.silent ) {
                  var dit = this;
                  Backbone.Relational.eventQueue.add( function() {
                      // The `changed` flag can be set in `handleAddition` or `handleRemoval`
                      if ( dit.changed ) {
                          dit.instance.trigger( 'change:' + dit.key, dit.instance, dit.related, options, true );
                          dit.changed = false;
                      }
                  });
              }
          },
  
          /**
           * When a model is added to a 'HasMany', trigger 'add' on 'this.instance' and notify reverse relations.
           * (should be 'HasOne', must set 'this.instance' as their related).
           */
          handleAddition: function( model, coll, options ) {
              //console.debug('handleAddition called; args=%o', arguments);
              options = options ? _.clone( options ) : {};
              this.changed = true;
  
              _.each( this.getReverseRelations( model ), function( relation ) {
                  relation.addRelated( this.instance, options );
              }, this );
  
              // Only trigger 'add' once the newly added model is initialized (so, has its relations set up)
              var dit = this;
              !options.silent && Backbone.Relational.eventQueue.add( function() {
                  dit.instance.trigger( 'add:' + dit.key, model, dit.related, options );
              });
          },
  
          /**
           * When a model is removed from a 'HasMany', trigger 'remove' on 'this.instance' and notify reverse relations.
           * (should be 'HasOne', which should be nullified)
           */
          handleRemoval: function( model, coll, options ) {
              //console.debug('handleRemoval called; args=%o', arguments);
              options = options ? _.clone( options ) : {};
              this.changed = true;
  
              _.each( this.getReverseRelations( model ), function( relation ) {
                  relation.removeRelated( this.instance, null, options );
              }, this );
  
              var dit = this;
              !options.silent && Backbone.Relational.eventQueue.add( function() {
                  dit.instance.trigger( 'remove:' + dit.key, model, dit.related, options );
              });
          },
  
          handleReset: function( coll, options ) {
              var dit = this;
              options = options ? _.clone( options ) : {};
              !options.silent && Backbone.Relational.eventQueue.add( function() {
                  dit.instance.trigger( 'reset:' + dit.key, dit.related, options );
              });
          },
  
          tryAddRelated: function( model, coll, options ) {
              var item = _.contains( this.keyIds, model.id );
  
              if ( item ) {
                  this.addRelated( model, options );
                  this.keyIds = _.without( this.keyIds, model.id );
              }
          },
  
          addRelated: function( model, options ) {
              // Allow 'model' to set up its relations before proceeding.
              // (which can result in a call to 'addRelated' from a relation of 'model')
              var dit = this;
              model.queue( function() {
                  if ( dit.related && !dit.related.get( model ) ) {
                      dit.related.add( model, _.defaults( { parse: false }, options ) );
                  }
              });
          },
  
          removeRelated: function( model, coll, options ) {
              if ( this.related.get( model ) ) {
                  this.related.remove( model, options );
              }
          }
      });
  
      /**
       * A type of Backbone.Model that also maintains relations to other models and collections.
       * New events when compared to the original:
       *  - 'add:<key>' (model, related collection, options)
       *  - 'remove:<key>' (model, related collection, options)
       *  - 'change:<key>' (model, related model or collection, options)
       */
      Backbone.RelationalModel = Backbone.Model.extend({
          relations: null, // Relation descriptions on the prototype
          _relations: null, // Relation instances
          _isInitialized: false,
          _deferProcessing: false,
          _queue: null,
          _attributeChangeFired: false, // Keeps track of `change` event firing under some conditions (like nested `set`s)
  
          subModelTypeAttribute: 'type',
          subModelTypes: null,
  
          constructor: function( attributes, options ) {
              // Nasty hack, for cases like 'model.get( <HasMany key> ).add( item )'.
              // Defer 'processQueue', so that when 'Relation.createModels' is used we trigger 'HasMany'
              // collection events only after the model is really fully set up.
              // Example: event for "p.on( 'add:jobs' )" -> "p.get('jobs').add( { company: c.id, person: p.id } )".
              if ( options && options.collection ) {
                  var dit = this,
                      collection = this.collection = options.collection;
  
                  // Prevent `collection` from cascading down to nested models; they shouldn't go into this `if` clause.
                  delete options.collection;
  
                  this._deferProcessing = true;
  
                  var processQueue = function( model ) {
                      if ( model === dit ) {
                          dit._deferProcessing = false;
                          dit.processQueue();
                          collection.off( 'relational:add', processQueue );
                      }
                  };
                  collection.on( 'relational:add', processQueue );
  
                  // So we do process the queue eventually, regardless of whether this model actually gets added to 'options.collection'.
                  _.defer( function() {
                      processQueue( dit );
                  });
              }
  
              Backbone.Relational.store.processOrphanRelations();
              Backbone.Relational.store.listenTo( this, 'relational:unregister', Backbone.Relational.store.unregister );
  
              this._queue = new Backbone.BlockingQueue();
              this._queue.block();
              Backbone.Relational.eventQueue.block();
  
              try {
                  Backbone.Model.apply( this, arguments );
              }
              finally {
                  // Try to run the global queue holding external events
                  Backbone.Relational.eventQueue.unblock();
              }
          },
  
          /**
           * Override 'trigger' to queue 'change' and 'change:*' events
           */
          trigger: function( eventName ) {
              if ( eventName.length > 5 && eventName.indexOf( 'change' ) === 0 ) {
                  var dit = this,
                      args = arguments;
  
                  if ( !Backbone.Relational.eventQueue.isLocked() ) {
                      // If we're not in a more complicated nested scenario, fire the change event right away
                      Backbone.Model.prototype.trigger.apply( dit, args );
                  }
                  else {
                      Backbone.Relational.eventQueue.add( function() {
                          // Determine if the `change` event is still valid, now that all relations are populated
                          var changed = true;
                          if ( eventName === 'change' ) {
                              // `hasChanged` may have gotten reset by nested calls to `set`.
                              changed = dit.hasChanged() || dit._attributeChangeFired;
                              dit._attributeChangeFired = false;
                          }
                          else {
                              var attr = eventName.slice( 7 ),
                                  rel = dit.getRelation( attr );
  
                              if ( rel ) {
                                  // If `attr` is a relation, `change:attr` get triggered from `Relation.onChange`.
                                  // These take precedence over `change:attr` events triggered by `Model.set`.
                                  // The relation sets a fourth attribute to `true`. If this attribute is present,
                                  // continue triggering this event; otherwise, it's from `Model.set` and should be stopped.
                                  changed = ( args[ 4 ] === true );
  
                                  // If this event was triggered by a relation, set the right value in `this.changed`
                                  // (a Collection or Model instead of raw data).
                                  if ( changed ) {
                                      dit.changed[ attr ] = args[ 2 ];
                                  }
                                  // Otherwise, this event is from `Model.set`. If the relation doesn't report a change,
                                  // remove attr from `dit.changed` so `hasChanged` doesn't take it into account.
                                  else if ( !rel.changed ) {
                                      delete dit.changed[ attr ];
                                  }
                              }
                              else if ( changed ) {
                                  dit._attributeChangeFired = true;
                              }
                          }
  
                          changed && Backbone.Model.prototype.trigger.apply( dit, args );
                      });
                  }
              }
              else if ( eventName === 'destroy' ) {
                  Backbone.Model.prototype.trigger.apply( this, arguments );
                  Backbone.Relational.store.unregister( this );
              }
              else {
                  Backbone.Model.prototype.trigger.apply( this, arguments );
              }
  
              return this;
          },
  
          /**
           * Initialize Relations present in this.relations; determine the type (HasOne/HasMany), then creates a new instance.
           * Invoked in the first call so 'set' (which is made from the Backbone.Model constructor).
           */
          initializeRelations: function( options ) {
              this.acquire(); // Setting up relations often also involve calls to 'set', and we only want to enter this function once
              this._relations = {};
  
              _.each( this.relations || [], function( rel ) {
                  Backbone.Relational.store.initializeRelation( this, rel, options );
              }, this );
  
              this._isInitialized = true;
              this.release();
              this.processQueue();
          },
  
          /**
           * When new values are set, notify this model's relations (also if options.silent is set).
           * (called from `set`; Relation.setRelated locks this model before calling 'set' on it to prevent loops)
           * @param {Object} [changedAttrs]
           * @param {Object} [options]
           */
          updateRelations: function( changedAttrs, options ) {
              if ( this._isInitialized && !this.isLocked() ) {
                  _.each( this._relations, function( rel ) {
                      if ( !changedAttrs || ( rel.keySource in changedAttrs || rel.key in changedAttrs ) ) {
                          // Fetch data in `rel.keySource` if data got set in there, or `rel.key` otherwise
                          var value = this.attributes[ rel.keySource ] || this.attributes[ rel.key ],
                              attr = changedAttrs && ( changedAttrs[ rel.keySource ] || changedAttrs[ rel.key ] );
  
                          // Update a relation if its value differs from this model's attributes, or it's been explicitly nullified.
                          // Which can also happen before the originally intended related model has been found (`val` is null).
                          if ( rel.related !== value || ( value === null && attr === null ) ) {
                              this.trigger( 'relational:change:' + rel.key, this, value, options || {} );
                          }
                      }
  
                      // Explicitly clear 'keySource', to prevent a leaky abstraction if 'keySource' differs from 'key'.
                      if ( rel.keySource !== rel.key ) {
                          delete this.attributes[ rel.keySource ];
                      }
                  }, this );
              }
          },
  
          /**
           * Either add to the queue (if we're not initialized yet), or execute right away.
           */
          queue: function( func ) {
              this._queue.add( func );
          },
  
          /**
           * Process _queue
           */
          processQueue: function() {
              if ( this._isInitialized && !this._deferProcessing && this._queue.isBlocked() ) {
                  this._queue.unblock();
              }
          },
  
          /**
           * Get a specific relation.
           * @param {string} attr The relation key to look for.
           * @return {Backbone.Relation} An instance of 'Backbone.Relation', if a relation was found for 'attr', or null.
           */
          getRelation: function( attr ) {
              return this._relations[ attr ];
          },
  
          /**
           * Get all of the created relations.
           * @return {Backbone.Relation[]}
           */
          getRelations: function() {
              return _.values( this._relations );
          },
  
  
          /**
           * Get a list of ids that will be fetched on a call to `getAsync`.
           * @param {string|Backbone.Relation} attr The relation key to fetch models for.
           * @param [refresh=false] Add ids for models that are already in the relation, refreshing them?
           * @return {Array} An array of ids that need to be fetched.
           */
          getIdsToFetch: function( attr, refresh ) {
              var rel = attr instanceof Backbone.Relation ? attr : this.getRelation( attr ),
                  ids = rel ? ( rel.keyIds && rel.keyIds.slice( 0 ) ) || ( ( rel.keyId || rel.keyId === 0 ) ? [ rel.keyId ] : [] ) : [];
  
              // On `refresh`, add the ids for current models in the relation to `idsToFetch`
              if ( refresh ) {
                  var models = rel.related && ( rel.related.models || [ rel.related ] );
                  _.each( models, function( model ) {
                      if ( model.id || model.id === 0 ) {
                          ids.push( model.id );
                      }
                  });
              }
  
              return ids;
          },
  
          /**
           * Get related objects. Returns a single promise, which can either resolve immediately (if the related model[s])
           * are already present locally, or after fetching the contents of the requested attribute.
           * @param {string} attr The relation key to fetch models for.
           * @param {Object} [options] Options for 'Backbone.Model.fetch' and 'Backbone.sync'.
           * @param {Boolean} [options.refresh=false] Fetch existing models from the server as well (in order to update them).
           * @return {jQuery.Deferred} A jQuery promise object. When resolved, its `done` callback will be called with
           *  contents of `attr`.
           */
          getAsync: function( attr, options ) {
              // Set default `options` for fetch
              options = _.extend( { add: true, remove: false, refresh: false }, options );
  
              var dit = this,
                  requests = [],
                  rel = this.getRelation( attr ),
                  idsToFetch = rel && this.getIdsToFetch( rel, options.refresh ),
                  coll = rel.related instanceof Backbone.Collection ? rel.related : rel.relatedCollection;
  
              if ( idsToFetch && idsToFetch.length ) {
                  var models = [],
                      createdModels = [],
                      setUrl,
                      createModels = function() {
                          // Find (or create) a model for each one that is to be fetched
                          models = _.map( idsToFetch, function( id ) {
                              var model = rel.relatedModel.findModel( id );
  
                              if ( !model ) {
                                  var attrs = {};
                                  attrs[ rel.relatedModel.prototype.idAttribute ] = id;
                                  model = rel.relatedModel.findOrCreate( attrs, options );
                                  createdModels.push( model );
                              }
  
                              return model;
                          }, this );
                      };
  
                  // Try if the 'collection' can provide a url to fetch a set of models in one request.
                  // This assumes that when 'Backbone.Collection.url' is a function, it can handle building of set urls.
                  // To make sure it can, test if the url we got by supplying a list of models to fetch is different from
                  // the one supplied for the default fetch action (without args to 'url').
                  if ( coll instanceof Backbone.Collection && _.isFunction( coll.url ) ) {
                      var defaultUrl = coll.url();
                      setUrl = coll.url( idsToFetch );
  
                      if ( setUrl === defaultUrl ) {
                          createModels();
                          setUrl = coll.url( models );
  
                          if ( setUrl === defaultUrl ) {
                              setUrl = null;
                          }
                      }
                  }
  
                  if ( setUrl ) {
                      // Do a single request to fetch all models
                      var opts = _.defaults(
                          {
                              error: function() {
                                  _.each( createdModels, function( model ) {
                                      model.trigger( 'destroy', model, model.collection, options );
                                  });
  
                                  options.error && options.error.apply( models, arguments );
                              },
                              url: setUrl
                          },
                          options
                      );
  
                      requests = [ coll.fetch( opts ) ];
                  }
                  else {
                      // Make a request per model to fetch
                      if  ( !models.length ) {
                          createModels();
                      }
  
                      requests = _.map( models, function( model ) {
                          var opts = _.defaults(
                              {
                                  error: function() {
                                      if ( _.contains( createdModels, model ) ) {
                                          model.trigger( 'destroy', model, model.collection, options );
                                      }
                                      options.error && options.error.apply( models, arguments );
                                  }
                              },
                              options
                          );
                          return model.fetch( opts );
                      }, this );
                  }
              }
  
              return $.when.apply( null, requests ).then(
                  function() {
                      return Backbone.Model.prototype.get.call( dit, attr );
                  }
              );
          },
  
          set: function( key, value, options ) {
              Backbone.Relational.eventQueue.block();
  
              // Duplicate backbone's behavior to allow separate key/value parameters, instead of a single 'attributes' object
              var attributes,
                  result;
  
              if ( _.isObject( key ) || key == null ) {
                  attributes = key;
                  options = value;
              }
              else {
                  attributes = {};
                  attributes[ key ] = value;
              }
  
              try {
                  var id = this.id,
                      newId = attributes && this.idAttribute in attributes && attributes[ this.idAttribute ];
  
                  // Check if we're not setting a duplicate id before actually calling `set`.
                  Backbone.Relational.store.checkId( this, newId );
  
                  result = Backbone.Model.prototype.set.apply( this, arguments );
  
                  // Ideal place to set up relations, if this is the first time we're here for this model
                  if ( !this._isInitialized && !this.isLocked() ) {
                      this.constructor.initializeModelHierarchy();
  
                      // Only register models that have an id. A model will be registered when/if it gets an id later on.
                      if ( newId || newId === 0 ) {
                          Backbone.Relational.store.register( this );
                      }
  
                      this.initializeRelations( options );
                  }
                  // The store should know about an `id` update asap
                  else if ( newId && newId !== id ) {
                      Backbone.Relational.store.update( this );
                  }
  
                  if ( attributes ) {
                      this.updateRelations( attributes, options );
                  }
              }
              finally {
                  // Try to run the global queue holding external events
                  Backbone.Relational.eventQueue.unblock();
              }
  
              return result;
          },
  
          clone: function() {
              var attributes = _.clone( this.attributes );
              if ( !_.isUndefined( attributes[ this.idAttribute ] ) ) {
                  attributes[ this.idAttribute ] = null;
              }
  
              _.each( this.getRelations(), function( rel ) {
                  delete attributes[ rel.key ];
              });
  
              return new this.constructor( attributes );
          },
  
          /**
           * Convert relations to JSON, omits them when required
           */
          toJSON: function( options ) {
              // If this Model has already been fully serialized in this branch once, return to avoid loops
              if ( this.isLocked() ) {
                  return this.id;
              }
  
              this.acquire();
              var json = Backbone.Model.prototype.toJSON.call( this, options );
  
              if ( this.constructor._superModel && !( this.constructor._subModelTypeAttribute in json ) ) {
                  json[ this.constructor._subModelTypeAttribute ] = this.constructor._subModelTypeValue;
              }
  
              _.each( this._relations, function( rel ) {
                  var related = json[ rel.key ],
                      includeInJSON = rel.options.includeInJSON,
                      value = null;
  
                  if ( includeInJSON === true ) {
                      if ( related && _.isFunction( related.toJSON ) ) {
                          value = related.toJSON( options );
                      }
                  }
                  else if ( _.isString( includeInJSON ) ) {
                      if ( related instanceof Backbone.Collection ) {
                          value = related.pluck( includeInJSON );
                      }
                      else if ( related instanceof Backbone.Model ) {
                          value = related.get( includeInJSON );
                      }
  
                      // Add ids for 'unfound' models if includeInJSON is equal to (only) the relatedModel's `idAttribute`
                      if ( includeInJSON === rel.relatedModel.prototype.idAttribute ) {
                          if ( rel instanceof Backbone.HasMany ) {
                              value = value.concat( rel.keyIds );
                          }
                          else if ( rel instanceof Backbone.HasOne ) {
                              value = value || rel.keyId;
  
                              if ( !value && !_.isObject( rel.keyContents ) ) {
                                  value = rel.keyContents || null;
                              }
                          }
                      }
                  }
                  else if ( _.isArray( includeInJSON ) ) {
                      if ( related instanceof Backbone.Collection ) {
                          value = [];
                          related.each( function( model ) {
                              var curJson = {};
                              _.each( includeInJSON, function( key ) {
                                  curJson[ key ] = model.get( key );
                              });
                              value.push( curJson );
                          });
                      }
                      else if ( related instanceof Backbone.Model ) {
                          value = {};
                          _.each( includeInJSON, function( key ) {
                              value[ key ] = related.get( key );
                          });
                      }
                  }
                  else {
                      delete json[ rel.key ];
                  }
  
                  // In case of `wait: true`, Backbone will simply push whatever's passed into `save` into attributes.
                  // We'll want to get this information into the JSON, even if it doesn't conform to our normal
                  // expectations of what's contained in it (no model/collection for a relation, etc).
                  if ( value === null && options && options.wait ) {
                      value = related;
                  }
  
                  if ( includeInJSON ) {
                      json[ rel.keyDestination ] = value;
                  }
  
                  if ( rel.keyDestination !== rel.key ) {
                      delete json[ rel.key ];
                  }
              });
  
              this.release();
              return json;
          }
      },
      {
          /**
           *
           * @param superModel
           * @returns {Backbone.RelationalModel.constructor}
           */
          setup: function( superModel ) {
              // We don't want to share a relations array with a parent, as this will cause problems with reverse
              // relations. Since `relations` may also be a property or function, only use slice if we have an array.
              this.prototype.relations = ( this.prototype.relations || [] ).slice( 0 );
  
              this._subModels = {};
              this._superModel = null;
  
              // If this model has 'subModelTypes' itself, remember them in the store
              if ( this.prototype.hasOwnProperty( 'subModelTypes' ) ) {
                  Backbone.Relational.store.addSubModels( this.prototype.subModelTypes, this );
              }
              // The 'subModelTypes' property should not be inherited, so reset it.
              else {
                  this.prototype.subModelTypes = null;
              }
  
              // Initialize all reverseRelations that belong to this new model.
              _.each( this.prototype.relations || [], function( rel ) {
                  if ( !rel.model ) {
                      rel.model = this;
                  }
  
                  if ( rel.reverseRelation && rel.model === this ) {
                      var preInitialize = true;
                      if ( _.isString( rel.relatedModel ) ) {
                          /**
                           * The related model might not be defined for two reasons
                           *  1. it is related to itself
                           *  2. it never gets defined, e.g. a typo
                           *  3. the model hasn't been defined yet, but will be later
                           * In neither of these cases do we need to pre-initialize reverse relations.
                           * However, for 3. (which is, to us, indistinguishable from 2.), we do need to attempt
                           * setting up this relation again later, in case the related model is defined later.
                           */
                          var relatedModel = Backbone.Relational.store.getObjectByName( rel.relatedModel );
                          preInitialize = relatedModel && ( relatedModel.prototype instanceof Backbone.RelationalModel );
                      }
  
                      if ( preInitialize ) {
                          Backbone.Relational.store.initializeRelation( null, rel );
                      }
                      else if ( _.isString( rel.relatedModel ) ) {
                          Backbone.Relational.store.addOrphanRelation( rel );
                      }
                  }
              }, this );
  
              return this;
          },
  
          /**
           * Create a 'Backbone.Model' instance based on 'attributes'.
           * @param {Object} attributes
           * @param {Object} [options]
           * @return {Backbone.Model}
           */
          build: function( attributes, options ) {
              // 'build' is a possible entrypoint; it's possible no model hierarchy has been determined yet.
              this.initializeModelHierarchy();
  
              // Determine what type of (sub)model should be built if applicable.
              var model = this._findSubModelType( this, attributes ) || this;
  
              return new model( attributes, options );
          },
  
          /**
           * Determines what type of (sub)model should be built if applicable.
           * Looks up the proper subModelType in 'this._subModels', recursing into
           * types until a match is found.  Returns the applicable 'Backbone.Model'
           * or null if no match is found.
           * @param {Backbone.Model} type
           * @param {Object} attributes
           * @return {Backbone.Model}
           */
          _findSubModelType: function( type, attributes ) {
              if ( type._subModels && type.prototype.subModelTypeAttribute in attributes ) {
                  var subModelTypeAttribute = attributes[ type.prototype.subModelTypeAttribute ];
                  var subModelType = type._subModels[ subModelTypeAttribute ];
                  if ( subModelType ) {
                      return subModelType;
                  }
                  else {
                      // Recurse into subModelTypes to find a match
                      for ( subModelTypeAttribute in type._subModels ) {
                          subModelType = this._findSubModelType( type._subModels[ subModelTypeAttribute ], attributes );
                          if ( subModelType ) {
                              return subModelType;
                          }
                      }
                  }
              }
  
              return null;
          },
  
          /**
           *
           */
          initializeModelHierarchy: function() {
              // Inherit any relations that have been defined in the parent model.
              this.inheritRelations();
  
              // If we came here through 'build' for a model that has 'subModelTypes' then try to initialize the ones that
              // haven't been resolved yet.
              if ( this.prototype.subModelTypes ) {
                  var resolvedSubModels = _.keys( this._subModels );
                  var unresolvedSubModels = _.omit( this.prototype.subModelTypes, resolvedSubModels );
                  _.each( unresolvedSubModels, function( subModelTypeName ) {
                      var subModelType = Backbone.Relational.store.getObjectByName( subModelTypeName );
                      subModelType && subModelType.initializeModelHierarchy();
                  });
              }
          },
  
          inheritRelations: function() {
              // Bail out if we've been here before.
              if ( !_.isUndefined( this._superModel ) && !_.isNull( this._superModel ) ) {
                  return;
              }
              // Try to initialize the _superModel.
              Backbone.Relational.store.setupSuperModel( this );
  
              // If a superModel has been found, copy relations from the _superModel if they haven't been inherited automatically
              // (due to a redefinition of 'relations').
              if ( this._superModel ) {
                  // The _superModel needs a chance to initialize its own inherited relations before we attempt to inherit relations
                  // from the _superModel. You don't want to call 'initializeModelHierarchy' because that could cause sub-models of
                  // this class to inherit their relations before this class has had chance to inherit it's relations.
                  this._superModel.inheritRelations();
                  if ( this._superModel.prototype.relations ) {
                      // Find relations that exist on the '_superModel', but not yet on this model.
                      var inheritedRelations = _.filter( this._superModel.prototype.relations || [], function( superRel ) {
                          return !_.any( this.prototype.relations || [], function( rel ) {
                              return superRel.relatedModel === rel.relatedModel && superRel.key === rel.key;
                          }, this );
                      }, this );
  
                      this.prototype.relations = inheritedRelations.concat( this.prototype.relations );
                  }
              }
              // Otherwise, make sure we don't get here again for this type by making '_superModel' false so we fail the
              // isUndefined/isNull check next time.
              else {
                  this._superModel = false;
              }
          },
  
          /**
           * Find an instance of `this` type in 'Backbone.Relational.store'.
           * A new model is created if no matching model is found, `attributes` is an object, and `options.create` is true.
           * - If `attributes` is a string or a number, `findOrCreate` will query the `store` and return a model if found.
           * - If `attributes` is an object and is found in the store, the model will be updated with `attributes` unless `options.merge` is `false`.
           * @param {Object|String|Number} attributes Either a model's id, or the attributes used to create or update a model.
           * @param {Object} [options]
           * @param {Boolean} [options.create=true]
           * @param {Boolean} [options.merge=true]
           * @param {Boolean} [options.parse=false]
           * @return {Backbone.RelationalModel}
           */
          findOrCreate: function( attributes, options ) {
              options || ( options = {} );
              var parsedAttributes = ( _.isObject( attributes ) && options.parse && this.prototype.parse ) ?
                  this.prototype.parse( _.clone( attributes ) ) : attributes;
  
              // If specified, use a custom `find` function to match up existing models to the given attributes.
              // Otherwise, try to find an instance of 'this' model type in the store
              var model = this.findModel( parsedAttributes );
  
              // If we found an instance, update it with the data in 'item' (unless 'options.merge' is false).
              // If not, create an instance (unless 'options.create' is false).
              if ( _.isObject( attributes ) ) {
                  if ( model && options.merge !== false ) {
                      // Make sure `options.collection` and `options.url` doesn't cascade to nested models
                      delete options.collection;
                      delete options.url;
  
                      model.set( parsedAttributes, options );
                  }
                  else if ( !model && options.create !== false ) {
                      model = this.build( parsedAttributes, _.defaults( { parse: false }, options ) );
                  }
              }
  
              return model;
          },
  
          /**
           * Find an instance of `this` type in 'Backbone.Relational.store'.
           * - If `attributes` is a string or a number, `find` will query the `store` and return a model if found.
           * - If `attributes` is an object and is found in the store, the model will be updated with `attributes` unless `options.merge` is `false`.
           * @param {Object|String|Number} attributes Either a model's id, or the attributes used to create or update a model.
           * @param {Object} [options]
           * @param {Boolean} [options.merge=true]
           * @param {Boolean} [options.parse=false]
           * @return {Backbone.RelationalModel}
           */
          find: function( attributes, options ) {
              options || ( options = {} );
              options.create = false;
              return this.findOrCreate( attributes, options );
          },
  
          /**
           * A hook to override the matching when updating (or creating) a model.
           * The default implementation is to look up the model by id in the store.
           * @param {Object} attributes
           * @returns {Backbone.RelationalModel}
           */
          findModel: function( attributes ) {
              return Backbone.Relational.store.find( this, attributes );
          }
      });
      _.extend( Backbone.RelationalModel.prototype, Backbone.Semaphore );
  
      /**
       * Override Backbone.Collection._prepareModel, so objects will be built using the correct type
       * if the collection.model has subModels.
       * Attempts to find a model for `attrs` in Backbone.store through `findOrCreate`
       * (which sets the new properties on it if found), or instantiates a new model.
       */
      Backbone.Collection.prototype.__prepareModel = Backbone.Collection.prototype._prepareModel;
      Backbone.Collection.prototype._prepareModel = function( attrs, options ) {
          var model;
  
          if ( attrs instanceof Backbone.Model ) {
              if ( !attrs.collection ) {
                  attrs.collection = this;
              }
              model = attrs;
          }
          else {
              options = options ? _.clone( options ) : {};
              options.collection = this;
  
              if ( typeof this.model.findOrCreate !== 'undefined' ) {
                  model = this.model.findOrCreate( attrs, options );
              }
              else {
                  model = new this.model( attrs, options );
              }
  
              if ( model && model.validationError ) {
                  this.trigger( 'invalid', this, attrs, options );
                  model = false;
              }
          }
  
          return model;
      };
  
  
      /**
       * Override Backbone.Collection.set, so we'll create objects from attributes where required,
       * and update the existing models. Also, trigger 'relational:add'.
       */
      var set = Backbone.Collection.prototype.__set = Backbone.Collection.prototype.set;
      Backbone.Collection.prototype.set = function( models, options ) {
          // Short-circuit if this Collection doesn't hold RelationalModels
          if ( !( this.model.prototype instanceof Backbone.RelationalModel ) ) {
              return set.call( this, models, options );
          }
  
          if ( options && options.parse ) {
              models = this.parse( models, options );
          }
  
          var singular = !_.isArray( models ),
              newModels = [],
              toAdd = [],
              model = null;
  
          models = singular ? ( models ? [ models ] : [] ) : _.clone( models );
  
          //console.debug( 'calling add on coll=%o; model=%o, options=%o', this, models, options );
          for ( var i = 0; i < models.length; i++ ) {
              model = models[i];
              if ( !( model instanceof Backbone.Model ) ) {
                  model = Backbone.Collection.prototype._prepareModel.call( this, model, options );
              }
              if ( model ) {
                  toAdd.push( model );
                  if ( !( this.get( model ) || this.get( model.cid ) ) ) {
                      newModels.push( model );
                  }
                  // If we arrive in `add` while performing a `set` (after a create, so the model gains an `id`),
                  // we may get here before `_onModelEvent` has had the chance to update `_byId`.
                  else if ( model.id !== null && model.id !== undefined ) {
                      this._byId[ model.id ] = model;
                  }
              }
          }
  
          // Add 'models' in a single batch, so the original add will only be called once (and thus 'sort', etc).
          // If `parse` was specified, the collection and contained models have been parsed now.
          toAdd = singular ? ( toAdd.length ? toAdd[ 0 ] : null ) : toAdd;
          var result = set.call( this, toAdd, _.defaults( { merge: false, parse: false }, options ) );
  
          for ( i = 0; i < newModels.length; i++ ) {
              model = newModels[i];
              // Fire a `relational:add` event for any model in `newModels` that has actually been added to the collection.
              if ( this.get( model ) || this.get( model.cid ) ) {
                  this.trigger( 'relational:add', model, this, options );
              }
          }
  
          return result;
      };
  
      /**
       * Override 'Backbone.Collection.remove' to trigger 'relational:remove'.
       */
      var remove = Backbone.Collection.prototype.__remove = Backbone.Collection.prototype.remove;
      Backbone.Collection.prototype.remove = function( models, options ) {
          // Short-circuit if this Collection doesn't hold RelationalModels
          if ( !( this.model.prototype instanceof Backbone.RelationalModel ) ) {
              return remove.call( this, models, options );
          }
  
          var singular = !_.isArray( models ),
              toRemove = [];
  
          models = singular ? ( models ? [ models ] : [] ) : _.clone( models );
          options || ( options = {} );
  
          //console.debug('calling remove on coll=%o; models=%o, options=%o', this, models, options );
          _.each( models, function( model ) {
              model = this.get( model ) || ( model && this.get( model.cid ) );
              model && toRemove.push( model );
          }, this );
  
          var result = remove.call( this, singular ? ( toRemove.length ? toRemove[ 0 ] : null ) : toRemove, options );
  
          _.each( toRemove, function( model ) {
              this.trigger( 'relational:remove', model, this, options );
          }, this );
  
          return result;
      };
  
      /**
       * Override 'Backbone.Collection.reset' to trigger 'relational:reset'.
       */
      var reset = Backbone.Collection.prototype.__reset = Backbone.Collection.prototype.reset;
      Backbone.Collection.prototype.reset = function( models, options ) {
          options = _.extend( { merge: true }, options );
          var result = reset.call( this, models, options );
  
          if ( this.model.prototype instanceof Backbone.RelationalModel ) {
              this.trigger( 'relational:reset', this, options );
          }
  
          return result;
      };
  
      /**
       * Override 'Backbone.Collection.sort' to trigger 'relational:reset'.
       */
      var sort = Backbone.Collection.prototype.__sort = Backbone.Collection.prototype.sort;
      Backbone.Collection.prototype.sort = function( options ) {
          var result = sort.call( this, options );
  
          if ( this.model.prototype instanceof Backbone.RelationalModel ) {
              this.trigger( 'relational:reset', this, options );
          }
  
          return result;
      };
  
      /**
       * Override 'Backbone.Collection.trigger' so 'add', 'remove' and 'reset' events are queued until relations
       * are ready.
       */
      var trigger = Backbone.Collection.prototype.__trigger = Backbone.Collection.prototype.trigger;
      Backbone.Collection.prototype.trigger = function( eventName ) {
          // Short-circuit if this Collection doesn't hold RelationalModels
          if ( !( this.model.prototype instanceof Backbone.RelationalModel ) ) {
              return trigger.apply( this, arguments );
          }
  
          if ( eventName === 'add' || eventName === 'remove' || eventName === 'reset' || eventName === 'sort' ) {
              var dit = this,
                  args = arguments;
  
              if ( _.isObject( args[ 3 ] ) ) {
                  args = _.toArray( args );
                  // the fourth argument is the option object.
                  // we need to clone it, as it could be modified while we wait on the eventQueue to be unblocked
                  args[ 3 ] = _.clone( args[ 3 ] );
              }
  
              Backbone.Relational.eventQueue.add( function() {
                  trigger.apply( dit, args );
              });
          }
          else {
              trigger.apply( this, arguments );
          }
  
          return this;
      };
  
      // Override .extend() to automatically call .setup()
      Backbone.RelationalModel.extend = function( protoProps, classProps ) {
          var child = Backbone.Model.extend.call( this, protoProps, classProps );
  
          child.setup( this );
  
          return child;
      };
  }));