Goals document

Goals document

We always start with the JavaScript-like magic scoping mojo!

    ((root) ->
      root = this
      _ = root._ || require 'underscore'
      F = {}

Non-determinism
---------------

Non-deterministic functions are functions that can have more (or less) than one result.  As known from logic, a binary relation xRy (where x ∈ X, y ∈ Y) can be represented by a *function*  `X -> PowerSet{Y}`. As usual in computer science, we interpret the set `PowerSet{Y}` as a multi-set (realized as a regular scheme list). Compare with SQL, which likewise uses multisets and sequences were sets are properly called for. Also compare with [Wadler's "representing failure as a list of successes."](http://citeseer.uark.edu:8080/citeseerx/showciting;jsessionid=FF5F5EAA9D94B1A8618C49C37451D762?cid=377301).

Thus, we represent a 'relation' (aka `non-deterministic function') as a regular CoffeeScript function that returns an array of possible results.

First, we define two primitive non-deterministic functions; one of them yields no result whatsoever for any argument; the other merely returns its argument as the sole result.

    F.succeed = (result) -> [result]
    F.fail = _.always []

We build more complex non-deterministic functions by combining the existing ones with the help of the following two combinators.

`(disjunction l r)` returns all the results of `l` and all the results of `r`, or returns no results only if neither `l` nor `r` returned any.  In that sense, it is analogous to the logical disjunctionunction.

    disjunction = (l, r) ->
      (x) -> _.cat(l(x), r(x))

`(conjunction l r)` looks like a functional composition of `r` and `l`.  Only `(l x)` may return several results, so we have to apply `r` to each of them.  Obviously `(conjunction fail f)` and `(conjunction f fail)` are both equivalent to `fail`: they return no results, ever. It that sense, `conjunction` is analogous to the logical conjunction.

    conjunction = (l, r) ->
      (x) -> _.mapcat(l(x), r)

JavaScript allows you to pass any number of arguments to a function.  Therefore, we can make a function `disj` that takes any number of arguments and performs a logical disjunction over each.  This makes this version of Sokuza Kanren a bit more flexible in that it allows you to nest any number of relations therein.

    F.disj = () ->
      return F.fail if _.isEmpty(arguments)
      disjunction(_.first(arguments),
	              F.disj.apply(this, _.rest(arguments)))

Likewise, the `conj` function accepts any number of clauses, nit just two as in the original Sokuza.

    F.conj = () ->
      clauses = _.toArray(arguments)
      return F.succeed if _.isEmpty(clauses)
      return _.first(clauses) if _.size(clauses) is 1
      conjunction(_.first(clauses),
                  (s) -> F.conj.apply(null, _.rest(clauses))(s))

And that's all that there is for the built-in non-deterministic functions.

# Knowledge representation
# ------------------------

One may think of regular variables as "certain knowledge": they give  names to definite values.  A logic variable then stands for "improvable ignorance".  An unbound logic variable represents no  knowledge at all; in other words, it represents the result of a measurement *before* we have done the measurement. A logic variable may be associated with a definite value, like 10. That means definite knowledge.  A logic variable may be associated with a semi-definite value, like `[$X]` where `$X` is an unbound variable. We know something about the original variable: it is associated with the array of one element.  We can't say though what that element is. A logic variable can be associated with another, unbound logic variable. In that case, we still don't know what precisely the original variable stands for. However, we can say that it represents the same thing as the other variable. So, our uncertainty is reduced.

I've chosen to represent logic variables with their own simple type.

    class LVar
      constructor: (@name) ->

I've also created a couple of helper functions for creating new variables and checking "variableness" to decouple the representation a bit.

    F.lvar = (name) -> new LVar(name)
    F.isLVar = (v) -> (v instanceof LVar)

I implement associations of logic variables and their values (aka, *bindings*) as a class holding a simple JavaScript object.  One may say that a substitution represents our current knowledge of the world.

    class Bindings
      constructor: (seed = {}) ->
        @binds = _.merge({}, seed)

There are actually two ways of implementing substitutions as associative list. If the variable `$x` is associated with `$y` and `$y` is associated with `1`, we could represent this knowledge as `{$x: 1, $y 1}`. It is easy to lookup the value associated with the variable then, via a simple access. OTH, if we have the binding `{$x:  $y}` and we wish to add the bindings of `$y` to `1`, we have to make rearrangements so to produce `{$x: 1, $y 1}`, or make the traversal on lookup (which we defer to `find` below).

However, if we use an association-list-like structure (arrays of pairs) then we can just record the associations as we learn them, without modifying the previous ones. If originally we knew `[[$x, $y]]` and later we learned that `$y` is associated with `1`, we can simply prepend the latter association, obtaining `[[$y, 1], [$x, $y]]`. So, adding new knowledge becomes fast. The lookup procedure becomes more complex though, as we have to chase the chains of variables. To obtain the value associated with `$x` in the latter substitution, we first lookup `$x`, obtain `$y` (another logic variable), then lookup `$y` finally obtaining `1`.  I prefer the object-representation since it's more idiomatic, but using an a-list provides an intuitively incremental way of representing knowledge: it is easier to backtrack if we later find out our knowledge leads to a contradiction.

      extend: (lvar, value) ->
        o = {}
        o[lvar.name] = value
        new Bindings(_.merge(@binds, o))
      has: (lvar) ->
        @binds.hasOwnProperty(lvar.name)

Find the value associated with `lvar` in the `Bindings` instance.  Return `lvar` itself if it is unbound. In miniKanren, this function is called `walk`.

    lookup: (lvar) ->
        return lvar if !F.isLVar(lvar)
        return this.lookup(@binds[lvar.name]) if this.has(lvar)
        lvar

Starting with an empty binding is akin to saying that we start with zero knowledge.

    F.ignorance = new Bindings()

As mentioned, because we overwrite bindings as we discover them the lookup logic is a little pernicious in the face of logic variables bound to other logic variables.

    find = (v, bindings) ->
      lvar = bindings.lookup(v)
      return lvar if F.isLVar(v)
      if _.isArray(lvar)
        if _.isEmpty(lvar)
          return lvar
        else
          return _.cons(find(_.first(lvar), bindings),
  		              find(_.rest(lvar), bindings))
      lvar

# Unification
# -----------

Unification is the process of improving knowledge: or, the process of measurement. That measurement may uncover a contradiction though (things are not what we thought them to be). To be precise, the unification is the statement that two terms are the same. For example, unification of `1` and `1` is successful -- `1` is indeed the same as `1`. That doesn't add however to our knowledge of the world. If the logic variable `$x` is associated with `1` in the current bindings, the unification of `$x` with `2` yields a contradiction (the new measurement is not consistent with the previous measurements / hypotheses). Unification of an unbound logic variable `$x` and `1` improves our knowledge: the "measurement" found that `$x` is actually `1`. We record that fact in the new substitution.

Return the new bindings, or `null` on contradiction:

    F.unify = (l, r, bindings) ->

Find out what `l` actually is given our knowledge contained in `bindings`:

      t1 = bindings.lookup(l)

Find out what `r` actually is given our knowledge contained in `bindings`:

      t2 = bindings.lookup(r)

If `l` and `r` are the same; no new knowledge:

      if _.isEqual(t1, t2)
        return s

`l` is an unbound variable:

      if F.isLVar(t1)
        return bindings.extend(t1, t2)

`r` is an unbound variable:

      if F.isLVar(t2)
        return bindings.extend(t2, t1)

If t1 is a pair, so must be `r`.  This means that I can only unify arrays of nested arrays bottoming out on values or objects.  I cannot unify objects at the moment.

      if _.isArray(t1) && _.isArray(t2)
        s = F.unify(_.first(t1), _.first(t2), bindings)
        s = if (s isnt null) then F.unify(_.rest(t1), _.rest(t2),   bindings) else s
        return s
      return null

# Operational logic
# -----------------

Now we can combine non-deterministic functions (Part 1) and the representation of knowledge (Part 2) into a logic system.  We introduce a `goal` -- a non-deterministic function that takes a substitution and produces 0, 1 or more other bindings (new knowledge). In case the goal produces 0 bindings, we say that the goal failed. We will call any result produced by the goal an "outcome".

The functions `succeed` and `fail` defined earlier are obviously  goals.  The latter is the failing goal. OTH, `succeed` is the trivial successful goal, a tautology that doesn't improve our knowledge of the world. We can now add another primitive goal, the result of a "measurement".  The quantum-mechanical connotations of "the measurement" must be obvious by now.

    F.goal = (l, r) ->
      (bindings) ->
        result = F.unify(l, r, bindings)
        return F.succeed(result) if result isnt null
        return F.fail(bindings)

We also need a way to 'run' a goal, to see what knowledge we can obtain starting from sheer ignorance

    F.run = (goal) ->
      goal(F.ignorance)

# Logico
# ------

  F.choice = ($v, list) ->
    return F.fail if _.isEmpty(list)

    F.disj(F.goal($v, _.first(list)),
                  F.choice($v, _.rest(list)))

  # Exports and sundries
  # --------------------

  if module?
    module.exports = F
  else
    root.F = F

)(this)

We always start with the JavaScript-like magic scoping mojo!

    ((root) ->
      root = this
      _ = root._ || require 'underscore'
      F = {}

Non-determinism
---------------

Non-deterministic functions are functions that can have more (or less) than one result.  As known from logic, a binary relation xRy (where x ∈ X, y ∈ Y) can be represented by a *function*  `X -> PowerSet{Y}`. As usual in computer science, we interpret the set `PowerSet{Y}` as a multi-set (realized as a regular scheme list). Compare with SQL, which likewise uses multisets and sequences were sets are properly called for. Also compare with [Wadler's "representing failure as a list of successes."](http://citeseer.uark.edu:8080/citeseerx/showciting;jsessionid=FF5F5EAA9D94B1A8618C49C37451D762?cid=377301).

Thus, we represent a 'relation' (aka `non-deterministic function') as a regular CoffeeScript function that returns an array of possible results.

First, we define two primitive non-deterministic functions; one of them yields no result whatsoever for any argument; the other merely returns its argument as the sole result.

    F.succeed = (result) -> [result]
    F.fail = _.always []

We build more complex non-deterministic functions by combining the existing ones with the help of the following two combinators.

`(disjunction l r)` returns all the results of `l` and all the results of `r`, or returns no results only if neither `l` nor `r` returned any.  In that sense, it is analogous to the logical disjunctionunction.

    disjunction = (l, r) ->
      (x) -> _.cat(l(x), r(x))

`(conjunction l r)` looks like a functional composition of `r` and `l`.  Only `(l x)` may return several results, so we have to apply `r` to each of them.  Obviously `(conjunction fail f)` and `(conjunction f fail)` are both equivalent to `fail`: they return no results, ever. It that sense, `conjunction` is analogous to the logical conjunction.

    conjunction = (l, r) ->
      (x) -> _.mapcat(l(x), r)

JavaScript allows you to pass any number of arguments to a function.  Therefore, we can make a function `disj` that takes any number of arguments and performs a logical disjunction over each.  This makes this version of Sokuza Kanren a bit more flexible in that it allows you to nest any number of relations therein.

    F.disj = () ->
      return F.fail if _.isEmpty(arguments)
      disjunction(_.first(arguments),
	              F.disj.apply(this, _.rest(arguments)))

Likewise, the `conj` function accepts any number of clauses, nit just two as in the original Sokuza.

    F.conj = () ->
      clauses = _.toArray(arguments)
      return F.succeed if _.isEmpty(clauses)
      return _.first(clauses) if _.size(clauses) is 1
      conjunction(_.first(clauses),
                  (s) -> F.conj.apply(null, _.rest(clauses))(s))

And that's all that there is for the built-in non-deterministic functions.

# Knowledge representation
# ------------------------

One may think of regular variables as "certain knowledge": they give  names to definite values.  A logic variable then stands for "improvable ignorance".  An unbound logic variable represents no  knowledge at all; in other words, it represents the result of a measurement *before* we have done the measurement. A logic variable may be associated with a definite value, like 10. That means definite knowledge.  A logic variable may be associated with a semi-definite value, like `[$X]` where `$X` is an unbound variable. We know something about the original variable: it is associated with the array of one element.  We can't say though what that element is. A logic variable can be associated with another, unbound logic variable. In that case, we still don't know what precisely the original variable stands for. However, we can say that it represents the same thing as the other variable. So, our uncertainty is reduced.

I've chosen to represent logic variables with their own simple type.

    class LVar
      constructor: (@name) ->

I've also created a couple of helper functions for creating new variables and checking "variableness" to decouple the representation a bit.

    F.lvar = (name) -> new LVar(name)
    F.isLVar = (v) -> (v instanceof LVar)

I implement associations of logic variables and their values (aka, *bindings*) as a class holding a simple JavaScript object.  One may say that a substitution represents our current knowledge of the world.

    class Bindings
      constructor: (seed = {}) ->
        @binds = _.merge({}, seed)

There are actually two ways of implementing substitutions as associative list. If the variable `$x` is associated with `$y` and `$y` is associated with `1`, we could represent this knowledge as `{$x: 1, $y 1}`. It is easy to lookup the value associated with the variable then, via a simple access. OTH, if we have the binding `{$x:  $y}` and we wish to add the bindings of `$y` to `1`, we have to make rearrangements so to produce `{$x: 1, $y 1}`, or make the traversal on lookup (which we defer to `find` below).

However, if we use an association-list-like structure (arrays of pairs) then we can just record the associations as we learn them, without modifying the previous ones. If originally we knew `[[$x, $y]]` and later we learned that `$y` is associated with `1`, we can simply prepend the latter association, obtaining `[[$y, 1], [$x, $y]]`. So, adding new knowledge becomes fast. The lookup procedure becomes more complex though, as we have to chase the chains of variables. To obtain the value associated with `$x` in the latter substitution, we first lookup `$x`, obtain `$y` (another logic variable), then lookup `$y` finally obtaining `1`.  I prefer the object-representation since it's more idiomatic, but using an a-list provides an intuitively incremental way of representing knowledge: it is easier to backtrack if we later find out our knowledge leads to a contradiction.

      extend: (lvar, value) ->
        o = {}
        o[lvar.name] = value
        new Bindings(_.merge(@binds, o))
      has: (lvar) ->
        @binds.hasOwnProperty(lvar.name)

Find the value associated with `lvar` in the `Bindings` instance.  Return `lvar` itself if it is unbound. In miniKanren, this function is called `walk`.

    lookup: (lvar) ->
        return lvar if !F.isLVar(lvar)
        return this.lookup(@binds[lvar.name]) if this.has(lvar)
        lvar

Starting with an empty binding is akin to saying that we start with zero knowledge.

    F.ignorance = new Bindings()

As mentioned, because we overwrite bindings as we discover them the lookup logic is a little pernicious in the face of logic variables bound to other logic variables.

    find = (v, bindings) ->
      lvar = bindings.lookup(v)
      return lvar if F.isLVar(v)
      if _.isArray(lvar)
        if _.isEmpty(lvar)
          return lvar
        else
          return _.cons(find(_.first(lvar), bindings),
  		              find(_.rest(lvar), bindings))
      lvar

# Unification
# -----------

Unification is the process of improving knowledge: or, the process of measurement. That measurement may uncover a contradiction though (things are not what we thought them to be). To be precise, the unification is the statement that two terms are the same. For example, unification of `1` and `1` is successful -- `1` is indeed the same as `1`. That doesn't add however to our knowledge of the world. If the logic variable `$x` is associated with `1` in the current bindings, the unification of `$x` with `2` yields a contradiction (the new measurement is not consistent with the previous measurements / hypotheses). Unification of an unbound logic variable `$x` and `1` improves our knowledge: the "measurement" found that `$x` is actually `1`. We record that fact in the new substitution.

Return the new bindings, or `null` on contradiction:

    F.unify = (l, r, bindings) ->

Find out what `l` actually is given our knowledge contained in `bindings`:

      t1 = bindings.lookup(l)

Find out what `r` actually is given our knowledge contained in `bindings`:

      t2 = bindings.lookup(r)

If `l` and `r` are the same; no new knowledge:

      if _.isEqual(t1, t2)
        return s

`l` is an unbound variable:

      if F.isLVar(t1)
        return bindings.extend(t1, t2)

`r` is an unbound variable:

      if F.isLVar(t2)
        return bindings.extend(t2, t1)

If t1 is a pair, so must be `r`.  This means that I can only unify arrays of nested arrays bottoming out on values or objects.  I cannot unify objects at the moment.

      if _.isArray(t1) && _.isArray(t2)
        s = F.unify(_.first(t1), _.first(t2), bindings)
        s = if (s isnt null) then F.unify(_.rest(t1), _.rest(t2),   bindings) else s
        return s
      return null

  # Operational logic
  # -----------------

  F.goal = (l, r) ->
    (bindings) ->
      result = F.unify(l, r, bindings)
      return F.succeed(result) if result isnt null
      return F.fail(bindings)

  F.run = (goal) ->
    goal(F.ignorance)

  # Logico
  # ------

  F.choice = ($v, list) ->
    return F.fail if _.isEmpty(list)

    F.disj(F.goal($v, _.first(list)),
                  F.choice($v, _.rest(list)))

  # Exports and sundries
  # --------------------

  if module?
    module.exports = F
  else
    root.F = F

)(this)


less words

less words

# /api/App Components/Batman.Model

For a general explanation of `Batman.Model` and how it works, see [the guide](/docs/models.html).

_Note_: This documentation uses the term _model_ to refer to the class `Model`
or a `Model` subclass, and the term _record_ to refer to one instance of a
model.

## @.primaryKey[= "id"] : String

Defines the `Model`'s primary key. This attribute will be used for determining:

- record identity (ie, records with the same `primaryKey` are assumed to be the same record)
- whether a record [`isNew`](/docs/api/batman.model.html#prototype_function_isnew)
- whether records are related (see [`Batman.Model` Associations](/docs/api/batman.model_associations.html))
- URL parameters via [`toParam`](/docs/api/batman.model.html#prototype_function_toparam)

Change the option using `set`, like so:

    test 'primary key can be set using @set', ->
      class Shop extends Batman.Model
        @set 'primaryKey', 'shop_id'
      equal Shop.get('primaryKey'), 'shop_id'

## @.resourceName[= null] : String

`resourceName` is a minification-safe identifier for the `Model`. It is usually an underscore-cased version of the `Model`'s class name (for example, `App.BlogPost => "blog_post"`) . It is used by:

- Model assocations (for providing default `primaryKey`s and `foreignKey`s and for `urlNestsUnder`)
- Storage adapters (unless overriden by `storageKey`)
- `data-route` bindings (eg, `routes.items[item]`)

## @.storageKey[= null] : String

`storageKey` is used as a namespace by the model's storage adapter. `Batman.LocalStorage` and `Batman.SessionStorage` use it as a JSON namespace and `Batman.RestStorage` uses it as a URL segment. If `storageKey` isn't set, `resourceName` may be used.

## @persist(mechanism : StorageAdapter) : StorageAdapter

`@persist` is how a `Model` subclass is told to persist itself by means of a `StorageAdapter`. `@persist` accepts either a `StorageAdapter` class or instance and will return either the instantiated class or the instance passed to it for further modification.

    test 'models can be told to persist via a storage adapter', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @persist TestStorageAdapter

      record = new Shop
      ok record.hasStorage()

    test '@persist returns the instantiated storage adapter', ->
      adapter = false
      class Shop extends Batman.Model
        @resourceName: 'shop'
        adapter = @persist TestStorageAdapter

      ok adapter instanceof Batman.StorageAdapter

    test '@persist accepts already instantiated storage adapters', ->
      adapter = new Batman.StorageAdapter
      adapter.someHandyConfigurationOption = true
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @persist adapter

      record = new Shop
      ok record.hasStorage()

## @encode(keys...[, encoderObject : [Object|Function]])

Specifies that `keys` will be persisted. Use it to white-list fields that should be loaded from JSON and sent back as JSON.

If no `encoderObject` is provided, the identity function (`(x) -> x`) will be used to encode and decode values.

If `encoderObject` is provided, it may have `encode`, `decode` and `as` properties, for example:

```coffeescript
@encode 'myProperty',
  decode: (value, key, incomingJSON, outgoingObject, record) -> # returns a value to set on the record
  encode: (value, key, builtJSON, record) ->                    # returns a value to put into the JSON
  as: "my_property"                                             # overrides "myProperty" as the JSON key
```

__`decode`__ is applied to _incoming JSON values_ before they're set on the record. It may be `false` to prevent receiving data from the storage adapter.

The `decode` function's arguments are:

 + `value` is the raw value received from the storage adapter.
 + `key` is the key that `value` is stored under on the incoming data.
 + `incomingJSON` is the object which is being decoded into the `record`. This can be used to create compound key decoders.
 + `outgoingObject` is the object built up by the decoders and mixed into the record.
 + `record` is the record on which `fromJSON` has been called.

__`encode`__ is applied to _outgoing record values_ before they're added to the JSON. It may be set to `false` to prevent sending data to the storage adapter.

The `encode` function's arguments are:

 + `value` is the client side value of the `key` on the `record`
 + `key` is the key that `value` is stored under on the `record`. This is useful when passing the same `encoderObject` which needs to pivot on what key is being encoded to different calls to `encode`.
 + `builtJSON` is the object passed to and modified by each encoder, and eventually becomes the return value of the `toJSON` call.
 + `record` is the record on which `toJSON` has been called.

__`as`__ will override the `encode` key when getting and setting values from JSON. It may be a string or a function.

If `as` is a function, it will receive the following arguments:

 + `key` is the name which the `value` is stored under in the raw data.
 + `value` is the `value` of the `key` which will end up on the `record`.
 + `data` is the object which is modified by each encoder or decoder.
 + `record` is the record on which `toJSON` or `fromJSON` has been called.

_Note_: `Batman.Model` subclasses have no encoders by default, except for the model's `primaryKey`.

    test '@encode accepts a list of keys which are used during decoding', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @encode 'name', 'url', 'email', 'country'

      json = {name: "Snowdevil", url: "snowdevil.ca"}
      record = new Shop()
      record.fromJSON(json)
      equal record.get('name'), "Snowdevil"

    test '@encode accepts a list of keys which are used during encoding', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @encode 'name', 'url', 'email', 'country'

      record = new Shop(name: "Snowdevil", url: "snowdevil.ca")
      deepEqual record.toJSON(), {name: "Snowdevil", url: "snowdevil.ca"}

    test '@encode accepts custom encoders', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @encode 'name',
          encode: (name) -> name.toUpperCase()

      record = new Shop(name: "Snowdevil")
      deepEqual record.toJSON(), {name: "SNOWDEVIL"}

    test '@encode accepts custom decoders', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @encode 'name',
          decode: (name) -> name.replace('_', ' ')

      record = new Shop()
      record.fromJSON {name: "Snow_devil"}
      equal record.get('name'), "Snow devil"

    test '@encode can be passed an encoderObject with false to prevent the default encoder or decoder', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @encode 'name', {encode: false, decode: (x) -> x}
        @encode 'url'

      record = new Shop()
      record.fromJSON {name: "Snowdevil", url: "snowdevil.ca"}
      equal record.get('name'), 'Snowdevil'
      equal record.get('url'), "snowdevil.ca"
      deepEqual record.toJSON(), {url: "snowdevil.ca"}, 'The name key is absent because of encode: false'

    test '@encode accepts an as option to encode a key under a name which differs from that in the raw data', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @encode 'countryCode',
          as: 'country_code'
          encode: @defaultEncoder.encode
          decode: @defaultEncoder.decode

      record = new Shop(countryCode: 'SE')
      deepEqual record.toJSON(), {country_code: 'SE'}

Some more handy examples:

    test '@encode can be used to turn comma separated values into arrays', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'tags',
          decode: (string) -> string.split(', ')
          encode: (array) -> array.join(', ')

      record = new Post()
      record.fromJSON({tags: 'new, hot, cool'})
      deepEqual record.get('tags'), ['new', 'hot', 'cool']
      deepEqual record.toJSON(), {tags: 'new, hot, cool'}

    test '@encode can be used to turn arrays into sets', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'tags',
          decode: (array) -> new Batman.Set(array...)
          encode: (set) -> set.toArray()

      record = new Post()
      record.fromJSON({tags: ['new', 'hot', 'cool']})
      ok record.get('tags') instanceof Batman.Set
      deepEqual record.toJSON(), {tags: ['new', 'hot', 'cool']}

    test '@encode accepts the as option as a function', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @encode 'countryCode',
          as: (key) -> Batman.helpers.underscore(key)
          encode: @defaultEncoder.encode
          decode: @defaultEncoder.decode

      record = new Shop(countryCode: 'SE')
      deepEqual record.toJSON(), {country_code: 'SE'}

## @validate(keys...[, options : [Object|Function]])

Assigns validators to `keys` based on `options`. All instances of the defined model will be validated according to these keys.

See [Model Validations](/docs/api/batman.model_validations.html) for a detailed description of validation options.

See [`Model::validate`](/docs/api/batman.model.html#prototype_function_validate) for information on how to get a particular record's validity.

## @%loaded : Set

The `loaded` set is available on every model class and holds every model instance seen by the system in order to function as an identity map. Successfully loading or saving individual records or batches of records will result in those records being added to the `loaded` set. Destroying instances will remove records from the identity set.

    test 'the loaded set stores all records seen', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @persist TestStorageAdapter
        @encode 'name'

      ok Post.get('loaded') instanceof Batman.Set
      equal Post.get('loaded.length'), 0
      post = new Post()
      post.save()
      equal Post.get('loaded.length'), 1

    test 'the loaded adds new records caused by loads and removes records caused by destroys', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'

      adapter = new TestStorageAdapter(Post)
      adapter.storage =
          'posts1': {name: "One", id:1}
          'posts2': {name: "Two", id:2}

      Post.persist(adapter)
      Post.load()
      equal Post.get('loaded.length'), 2
      post = false
      Post.find(1, (err, result) -> post = result)
      post.destroy()
      equal Post.get('loaded.length'), 1

## @%all : Set

The `all` set is an alias to the `loaded` set but with an added implicit `load` on the model. `Model.get('all')` will synchronously return the `loaded` set and asynchronously call `Model.load()` without options to load a batch of records and populate the set originally returned (the `loaded` set) with the records returned by the server.

_Note_: The notion of "all the records" is relative only to the client. It completely depends on the storage adapter in use and any backends which they may contact to determine what comes back during a `Model.load`. This means that if for example your API paginates records, the set found in `all` may hold on the first 50 records instead of the entire backend set.

`all` is useful for listing every instance of a model in a view, and since the `loaded` set will change when the `load` returns, it can be safely bound to.

    asyncTest 'the all set asynchronously fetches records when gotten', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'

      adapter = new AsyncTestStorageAdapter(Post)
      adapter.storage =
          'posts1': {name: "One", id:1}
          'posts2': {name: "Two", id:2}

      Post.persist(adapter)
      equal Post.get('all.length'), 0, "The synchronously returned set is empty"
      delay ->
        equal Post.get('all.length'), 2, "After the async load the set is populated"

## @clear() : Set

`Model.clear()` empties that `Model`'s identity map. This is useful for tests and other unnatural situations where records new to the system are guaranteed to be as such.

    test 'clearing a model removes all records from the identity map', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'

      adapter = new TestStorageAdapter(Post)
      adapter.storage =
          'posts1': {name: "One", id:1}
          'posts2': {name: "Two", id:2}
      Post.persist(adapter)
      Post.load()
      equal Post.get('loaded.length'), 2
      Post.clear()
      equal Post.get('loaded.length'), 0, "After clear() the loaded set is empty"

## @find(id, callback : Function) : Model

`Model.find()` retrieves a record with the specified `id` from the storage adapter and calls back with an error if one occurred and the record if the operation was successful. `find` delegates to the storage adapter the `Model` has been `@persist`ed with, so it is up to the storage adapter's semantics to determine what type of errors may return and the timeline on which the callback may be called. The `callback` is a required function which should adopt the node style callback signature which accepts two arguments: an error, and the record asked for. `find` returns an "unloaded" record which, following the load completion, will be populated with the data from the storage adapter.

_Note_: `find` gives two results to calling code: one immediately, and one later. `find` returns a record synchronously as it is called and calls back with a record, and importantly these two records are __not__ guaranteed to be the same instance. This is because batman.js maps the identities of incoming and outgoing records such that there is only ever one canonical instance representing a record, which is useful so bindings are always bound to the same thing. In practice, this means that calling code should use the record `find` calls back with if anything is going to bind to that object, which is most of the time. The returned record however remains useful for state inspection and bookkeeping.

    asyncTest '@find calls back the requested model if no error occurs', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'
        @persist AsyncTestStorageAdapter,
          storage:
            'posts2': {name: "Two", id:2}

      post = Post.find 2, (err, result) ->
        throw err if err
        post = result
      equal post.get('name'), undefined
      delay ->
        equal post.get('name'), "Two"

_Note_: `find` must be passed a callback function. This is for two reasons: calling code must be aware that `find`'s return value is not necessarily the canonical instance, and calling code must be able to handle errors.

    asyncTest '@find calls back with the error if an error occurs', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'
        @persist AsyncTestStorageAdapter

      error = false
      post = Post.find 3, (err, result) ->
        error = err
      delay ->
        ok error instanceof Error

## @load(options = {}, callback : Function)

`Model.load()` retrieves an array of records according to the given `options` from the storage adapter and calls back with an error if one occurred and the set of records if the operation was successful. `load` delegates to the storage adapter the `Model` has been `@persist`ed with, so it is up to the storage adapter's semantics to determine what the options do, what kind of errors may arise, and the timeline on which the callback may be called. The `callback` is a required function which should adopt the node style callback signature which accepts two arguments, an error, and the array of records. `load` returns undefined.

For the two main `StorageAdapter`s batman.js provides, the `options` do different things:

- For `Batman.LocalStorage`, `options` act as a filter. The adapter will scan all the records in `localStorage` and return only those records which match all the key/value pairs given in the options.
- For `Batman.RestStorage`, `options` are serialized into query parameters on the `GET` request.

It accepts a callback with two arguments: any error that occurred, and an array of loaded records.

    asyncTest '@load calls back an array of records retrieved from the storage adapter', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'
        @persist TestStorageAdapter,
          storage:
            'posts1': {name: "One", id:1}
            'posts2': {name: "Two", id:2}

      posts = false
      Post.load (err, result) ->
        throw err if err
        posts = result

      delay ->
        equal posts.length, 2
        equal posts[0].get('name'), "One"

    asyncTest '@load calls back with an empty array if no records are found', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'
        @persist TestStorageAdapter, storage: []

      posts = false
      Post.load (err, result) ->
        throw err if err
        posts = result

      delay ->
        equal posts.length, 0

## @create(attributes = {}, callback) : Model

`App.Model.create` is a convenience method that is essentially equivalent to
calling `(new App.Model).save()`:

    asyncTest "@create instantiates a new record instance and saves it", ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'
        @persist TestStorageAdapter, storage: []

      # Using new + save:
      record = new Post(name: 'aName')
      record.save()

      # Using create:
      otherRecord = Post.create name: 'aName', ->

      delay ->
        equal record.get('name'), otherRecord.get('name')
        equal record.isNew(), false
        equal otherRecord.isNew(), false

_Note_ : `attributes` is an empty object `{}` by default. This means the single-argument version of `create` accepts the callback, and not the attributes object.

## @findOrCreate(attributes = {}, callback) : Model

## @createFromJSON(attributes = {}) : Model

Returns an instance of the model based on `attributes`. If the `primaryKey` is present in `attributes`, the in-memory identity map will be searched for a match. If a match is found, it will be updated with `attributes` (without tracking) and returned. If the `primaryKey` isn't present, a new instance is added to the `loaded` set and returned.

Since `createFromJSON` checks the identity map, it's a great way to load data without duplicating records in memory.

## @createMultipleFromJSON(attributesArray: Array) : Array

Loads data from JSON like `Model.createFromJSON`, but `attributesArray` is an array of objects and returns an array of records. `createMultipleFromJSON` loads new records all at once, so `Model.loaded.itemsWereAdded` is only fired once.

## ::%id

A universally accessible accessor to the record's primary key. If the record's
primary key is `id` (the default), getting/setting this accessor simply passes
the call through to `id`, otherwise it proxies the call to the custom primary key.

    test "id proxies the primary key", ->
      class Post extends Batman.Model
        @primaryKey: 'name'

      post = new Post(name: 'Witty title')
      equal post.get('id'), 'Witty title'

      post.set('id', 'Wittier title')
      equal post.get('name'), 'Wittier title'

## ::isDirty() : Boolean

Returns `true` if any keys have been changed since the record was initialized or saved.

## ::%isDirty : Boolean

A bindable accessor on [`isDirty`](/docs/api/batman.model.html#prototype_function_isdirty).

## ::%dirtyKeys : Set

The [`Batman.Set`](/docs/api/batman.set.html) of keys which have been modified since the last time the record was saved.

## ::%errors : Batman.ErrorsSet

`errors` is a `Batman.ErrorsSet`, which is simply a [`Batman.Set`](/docs/api/batman.set.html) of [`Batman.ValidationError`](/docs/api/batman.validationerror.html)s present on the model instance.

- `user.get('errors')` returns the errors on the `user` record
- `user.get('errors.length')` returns the number of errors, total

You can also access the errors for a specific attribute of the record:

- `user.get('errors.email_address')` returns the errors on the `email_address` attribute
- `user.get('errors.email_address.length')` returns the number of errors on the `email_address` attribute

## ::constructor(idOrAttributes = {}) : Model

If `idOrAttributes` is an object, the values are mixed into the new record. Otherwise, `idOrAttrubutes` is set to the new record's [`id`](/docs/api/batman.model.html#prototype_accessor_id).

## ::isNew() : boolean

Returns true if the instance represents a record that hasn't yet been persisted to storage. The default implementation simply checks if `@get('id')` is undefined, but you can override this on your own models.

`isNew` is used to determine whether `record.save()` will perform a `create` action or a `save` action.

## ::%isNew : Boolean

A bindable accessor on [`isNew`](/docs/api/batman.model.html#prototype_function_isnew).

## updateAttributes(attributes) : Model

Mixes in `attributes` into the record (using `set`). Doesn't save the record.

## toString() : string

Returns a string representation suitable for debugging. By default this just contains the model's `resourceName` and `id`

## ::%attributes : Hash

`attributes` is a `Batman.Hash` where a record's attributes are stored. `Batman.Model`'s default accessor stores values in `attributes`, so it includes:

- attributes defined with `@encode`
- keys assigned with `set`, unless the key has a specifically defined accessor

But it doesn't include:

- keys that have specifically defined accessors (eg, `errors`, `lifecycle`, `isNew`)

A record's attributes are used by `Model::transaction` to create a deep copy of the record.

## ::toJSON() : Object

Returns a JavaScript object containing the attributes of the record, using any specified encoders.

    test "toJSON returns a JavaScript object with the record's attributes", ->
      class Criminal extends Batman.Model
        @encode "name", "notorious"

      criminal = new Criminal(name: "Talia al Ghul", notorious: true)
      criminal_json = criminal.toJSON()
      equal criminal_json.name, "Talia al Ghul"
      equal criminal_json.notorious, true

## ::fromJSON() : Model

Loads attributes from a bare object into this instance.

    test 'fromJSON overwrites existing attributes', ->
      class Criminal extends Batman.Model
        @encode "name", "notorious"

      criminal = new Criminal(name: "Dr. Jonathan Crane", notorious: false)
      new_params =
        name: "Scarecrow"
        notorious: true
      criminal.fromJSON(new_params)

      equal criminal.get("notorious"), true
      equal criminal.get("name"), "Scarecrow"

## ::toParam() : value

Returns a representation of the model suitable for use in a URL. By default, this is the record's `id`.

This method is used by the routing system for serializing records into a URL.

## ::hasStorage() : boolean

True when the record has a storage adapter defined.

## ::load(options = {}, callback)
`Load` tries to read the record from its storage adapter. The options object will be passed to the storage adapter when it performs the `read` operation. The callback takes three parameters: error, the loaded record, and the environment. `Load`ing a record clears all errors on that record.

If the read operation fails or if the record is in a state which doesn't permit `load`, (for example, calling `load` on a deleted record) the callback will be invoked with an error.

## ::save(options = {}, callback)
`Save` [validates](http://localhost:4000/docs/api/batman.model.html#prototype_function_validate) the record, and if it passes, fires the corresponding storage operation (defined by the `Batman.StorageAdapter` passed to  [`@persist`](/docs/api/batman.model.html#class_function_persist)). When the storage operation is complete, the callback is invoked with two parameters: any JavaScript error and the record.

If the record [`isNew`](/docs/api/batman.model.html#prototype_function_isnew), `save` performs a `create` operation. Otherwise, it performs a `save` operation.

If the record is not valid, the [validation errors](/docs/api/batman.validationerror.html) will be passed to the first parameter of the callback function and the storage operation will not be performed.

Available options include:
- `only`: A whitelist that will submit only the specified model attributes from the storage adapter.  This is useful when you want to do partial updates of a model without sending the full model content.  e.g., `options = {only: ['name', 'bio']}`
- `except`: A blacklist that will prevent specified model attributes from being transmitted from the storage adapter.  e.g., `options = {except: ['sensitive_data']}`

## ::destroy(options = {}, callback)

`Destroy` fires the corresponding storage operation. The callback takes three arguments: JavaScript Error, the record, and the environment. If the operation is successful, the record is removed from its Model's [`loaded`](/docs/api/batman.model.html#class_function_loaded) set.

```coffeescript
criminal = new Criminal name: "The penguin"
criminal.destroy (err, record, env) ->
  if err
    console.log "Oh no! #{record.get('name')} is still on the loose!"
```

If the record's current lifecycle state doesn't allow the `destroy` action, the callback will be invoked with a `Batman.StateMachine.InvalidTransitionError`. For example, this could occur if `destroy` is called on an already-destroyed record.

## ::validate(callback)

`Model::validate` checks the model against the validations declared in the model definition (with [`Model@validate`](/docs/api/batman.model.html#class_function_validate)). This method accepts a callback with two arguments: any JS error that occurred within the validator function, and the set of [`Batman.ValidationError`](/docs/api/batman.validationerror.html)s that the input generated.

For example:

    test "validate(callback) will call the callback only after all keys have been validated", ->
      class Product extends Batman.Model
        @validate 'name', 'price', presence: yes

      newProduct = new Product
      newProduct.validate (javascriptError, validationErrors) ->
        throw javascriptError if javascriptError
        equal validationErrors.length, 2
        equal newProduct.get('errors.length'), 2
        equal newProduct.get('errors.name.length'), 1
        equal newProduct.get('errors.price.length'), 1

## ::transaction() : Model

Creates a deep copy of the record instance based on its `"attributes"`, allowing it to be modified without affecting the original. Also mixes in `Batman.Transaction`.
Useful for implementing actions that can be cancelled.

To apply the changes made to a transaction, call `applyChanges`.
To apply changes and save the record after running validations, call `save`.

    test "transaction creates an independent clone of a record", ->
      record = new Batman.Model(name: 'Felix')

      transaction = record.transaction()
      transaction.set('name', 'Camouflage')
      equal transaction.get('name'), 'Camouflage'
      equal record.get('name'), 'Felix'

      transaction.applyChanges()
      equal record.get('name'), 'Camouflage'

## ::reflectOnAssociation(label : String)

Returns the `Batman.Association` for the record's association named by `label`.
Returns `null` if the association does not exist.

## ::reflectOnAllAssociations([type: String])

If `type` is passed (eg, `hasMany`), returns a `Batman.SimpleSet` of all associations of that type on the record.
If no type is passed, all associations are returned.
If the record has no associations, returns `null`.

# /api/App Components/Batman.Model

For a general explanation of `Batman.Model` and how it works, see [the guide](/docs/models.html).

_Note_: This documentation uses the term _model_ to refer to the class `Model`
or a `Model` subclass, and the term _record_ to refer to one instance of a
model.

## @.primaryKey[= "id"] : String

Defines the `Model`'s primary key. This attribute will be used for determining:

- record identity (ie, records with the same `primaryKey` are assumed to be the same record)
- whether a record [`isNew`](/docs/api/batman.model.html#prototype_function_isnew)
- whether records are related (see [`Batman.Model` Associations](/docs/api/batman.model_associations.html))
- URL parameters via [`toParam`](/docs/api/batman.model.html#prototype_function_toparam)

Change the option using `set`, like so:

    test 'primary key can be set using @set', ->
      class Shop extends Batman.Model
        @set 'primaryKey', 'shop_id'
      equal Shop.get('primaryKey'), 'shop_id'

## @.resourceName[= null] : String

`resourceName` is a minification-safe identifier for the `Model`. It is usually an underscore-cased version of the `Model`'s class name (for example, `App.BlogPost => "blog_post"`) . It is used by:

- Model assocations (for providing default `primaryKey`s and `foreignKey`s and for `urlNestsUnder`)
- Storage adapters (unless overriden by `storageKey`)
- `data-route` bindings (eg, `routes.items[item]`)

## @.storageKey[= null] : String

`storageKey` is used as a namespace by the model's storage adapter. `Batman.LocalStorage` and `Batman.SessionStorage` use it as a JSON namespace and `Batman.RestStorage` uses it as a URL segment. If `storageKey` isn't set, `resourceName` may be used.

## @persist(mechanism : StorageAdapter) : StorageAdapter

`@persist` is how a `Model` subclass is told to persist itself by means of a `StorageAdapter`. `@persist` accepts either a `StorageAdapter` class or instance and will return either the instantiated class or the instance passed to it for further modification.

    test 'models can be told to persist via a storage adapter', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @persist TestStorageAdapter

      record = new Shop
      ok record.hasStorage()

    test '@persist returns the instantiated storage adapter', ->
      adapter = false
      class Shop extends Batman.Model
        @resourceName: 'shop'
        adapter = @persist TestStorageAdapter

      ok adapter instanceof Batman.StorageAdapter

    test '@persist accepts already instantiated storage adapters', ->
      adapter = new Batman.StorageAdapter
      adapter.someHandyConfigurationOption = true
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @persist adapter

      record = new Shop
      ok record.hasStorage()

## @encode(keys...[, encoderObject : [Object|Function]])

Specifies that `keys` will be persisted with the `Batman.StorageAdapter` passed to `@persist`. Use it to white-list fields that should be loaded from JSON and sent back as JSON.

If no `encoderObject` is provided, the identity function (`(x) -> x`) will be used to encode and decode values.

If `encoderObject` is provided, it may have `encode`, `decode` and `as` properties, for example:

```coffeescript
@encode 'myProperty',
  decode: (value, key, incomingJSON, outgoingObject, record) -> # returns a value to set on the record
  encode: (value, key, builtJSON, record) ->                    # returns a value to put into the JSON
  as: "my_property"                                             # overrides "myProperty" as the JSON key
```

__`decode`__ is applied to _incoming JSON values_ before they're set on the record. It may be `false` to prevent receiving data from the storage adapter.

The `decode` function's arguments are:

 + `value` is the raw value received from the storage adapter.
 + `key` is the key that `value` is stored under on the incoming data.
 + `incomingJSON` is the object which is being decoded into the `record`. This can be used to create compound key decoders.
 + `outgoingObject` is the object built up by the decoders and mixed into the record.
 + `record` is the record on which `fromJSON` has been called.

__`encode`__ is applied to _outgoing record values_ before they're added to the JSON. It may be set to `false` to prevent sending data to the storage adapter.

The `encode` function's arguments are:

 + `value` is the client side value of the `key` on the `record`
 + `key` is the key that `value` is stored under on the `record`. This is useful when passing the same `encoderObject` which needs to pivot on what key is being encoded to different calls to `encode`.
 + `builtJSON` is the object passed to and modified by each encoder, and eventually becomes the return value of the `toJSON` call.
 + `record` is the record on which `toJSON` has been called.

__`as`__ will override the `encode` key when getting and setting values from JSON. It may be a string or a function.

If `as` is a function, it will receive the following arguments:

 + `key` is the name which the `value` is stored under in the raw data.
 + `value` is the `value` of the `key` which will end up on the `record`.
 + `data` is the object which is modified by each encoder or decoder.
 + `record` is the record on which `toJSON` or `fromJSON` has been called.

_Note_: `Batman.Model` subclasses have no encoders by default, except for the model's `primaryKey`.

    test '@encode accepts a list of keys which are used during decoding', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @encode 'name', 'url', 'email', 'country'

      json = {name: "Snowdevil", url: "snowdevil.ca"}
      record = new Shop()
      record.fromJSON(json)
      equal record.get('name'), "Snowdevil"

    test '@encode accepts a list of keys which are used during encoding', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @encode 'name', 'url', 'email', 'country'

      record = new Shop(name: "Snowdevil", url: "snowdevil.ca")
      deepEqual record.toJSON(), {name: "Snowdevil", url: "snowdevil.ca"}

    test '@encode accepts custom encoders', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @encode 'name',
          encode: (name) -> name.toUpperCase()

      record = new Shop(name: "Snowdevil")
      deepEqual record.toJSON(), {name: "SNOWDEVIL"}

    test '@encode accepts custom decoders', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @encode 'name',
          decode: (name) -> name.replace('_', ' ')

      record = new Shop()
      record.fromJSON {name: "Snow_devil"}
      equal record.get('name'), "Snow devil"

    test '@encode can be passed an encoderObject with false to prevent the default encoder or decoder', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @encode 'name', {encode: false, decode: (x) -> x}
        @encode 'url'

      record = new Shop()
      record.fromJSON {name: "Snowdevil", url: "snowdevil.ca"}
      equal record.get('name'), 'Snowdevil'
      equal record.get('url'), "snowdevil.ca"
      deepEqual record.toJSON(), {url: "snowdevil.ca"}, 'The name key is absent because of encode: false'

    test '@encode accepts an as option to encode a key under a name which differs from that in the raw data', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @encode 'countryCode',
          as: 'country_code'
          encode: @defaultEncoder.encode
          decode: @defaultEncoder.decode

      record = new Shop(countryCode: 'SE')
      deepEqual record.toJSON(), {country_code: 'SE'}

Some more handy examples:

    test '@encode can be used to turn comma separated values into arrays', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'tags',
          decode: (string) -> string.split(', ')
          encode: (array) -> array.join(', ')

      record = new Post()
      record.fromJSON({tags: 'new, hot, cool'})
      deepEqual record.get('tags'), ['new', 'hot', 'cool']
      deepEqual record.toJSON(), {tags: 'new, hot, cool'}

    test '@encode can be used to turn arrays into sets', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'tags',
          decode: (array) -> new Batman.Set(array...)
          encode: (set) -> set.toArray()

      record = new Post()
      record.fromJSON({tags: ['new', 'hot', 'cool']})
      ok record.get('tags') instanceof Batman.Set
      deepEqual record.toJSON(), {tags: ['new', 'hot', 'cool']}

    test '@encode accepts the as option as a function', ->
      class Shop extends Batman.Model
        @resourceName: 'shop'
        @encode 'countryCode',
          as: (key) -> Batman.helpers.underscore(key)
          encode: @defaultEncoder.encode
          decode: @defaultEncoder.decode

      record = new Shop(countryCode: 'SE')
      deepEqual record.toJSON(), {country_code: 'SE'}

## @validate(keys...[, options : [Object|Function]])

Assigns validators to `keys` based on `options`. All instances of the defined model will be validated according to these keys.

See [Model Validations](/docs/api/batman.model_validations.html) for a detailed description of validation options.

See [`Model::validate`](/docs/api/batman.model.html#prototype_function_validate) for information on how to get a particular record's validity.

## @%loaded : Set

The `loaded` set is available on every model class and holds every model instance seen by the system in order to function as an identity map. Successfully loading or saving individual records or batches of records will result in those records being added to the `loaded` set. Destroying instances will remove records from the identity set.

    test 'the loaded set stores all records seen', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @persist TestStorageAdapter
        @encode 'name'

      ok Post.get('loaded') instanceof Batman.Set
      equal Post.get('loaded.length'), 0
      post = new Post()
      post.save()
      equal Post.get('loaded.length'), 1

    test 'the loaded adds new records caused by loads and removes records caused by destroys', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'

      adapter = new TestStorageAdapter(Post)
      adapter.storage =
          'posts1': {name: "One", id:1}
          'posts2': {name: "Two", id:2}

      Post.persist(adapter)
      Post.load()
      equal Post.get('loaded.length'), 2
      post = false
      Post.find(1, (err, result) -> post = result)
      post.destroy()
      equal Post.get('loaded.length'), 1

## @%all : Set

The `all` set is an alias to the `loaded` set but with an added implicit `load` on the model. `Model.get('all')` will synchronously return the `loaded` set and asynchronously call `Model.load()` without options to load a batch of records and populate the set originally returned (the `loaded` set) with the records returned by the server.

_Note_: The notion of "all the records" is relative only to the client. It completely depends on the storage adapter in use and any backends which they may contact to determine what comes back during a `Model.load`. This means that if for example your API paginates records, the set found in `all` may hold on the first 50 records instead of the entire backend set.

`all` is useful for listing every instance of a model in a view, and since the `loaded` set will change when the `load` returns, it can be safely bound to.

    asyncTest 'the all set asynchronously fetches records when gotten', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'

      adapter = new AsyncTestStorageAdapter(Post)
      adapter.storage =
          'posts1': {name: "One", id:1}
          'posts2': {name: "Two", id:2}

      Post.persist(adapter)
      equal Post.get('all.length'), 0, "The synchronously returned set is empty"
      delay ->
        equal Post.get('all.length'), 2, "After the async load the set is populated"

## @clear() : Set

`Model.clear()` empties that `Model`'s identity map. This is useful for tests and other unnatural situations where records new to the system are guaranteed to be as such.

    test 'clearing a model removes all records from the identity map', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'

      adapter = new TestStorageAdapter(Post)
      adapter.storage =
          'posts1': {name: "One", id:1}
          'posts2': {name: "Two", id:2}
      Post.persist(adapter)
      Post.load()
      equal Post.get('loaded.length'), 2
      Post.clear()
      equal Post.get('loaded.length'), 0, "After clear() the loaded set is empty"

## @find(id, callback : Function) : Model

`Model.find()` retrieves a record with the specified `id` from the storage adapter and calls back with an error if one occurred and the record if the operation was successful. `find` delegates to the storage adapter the `Model` has been `@persist`ed with, so it is up to the storage adapter's semantics to determine what type of errors may return and the timeline on which the callback may be called. The `callback` is a required function which should adopt the node style callback signature which accepts two arguments: an error, and the record asked for. `find` returns an "unloaded" record which, following the load completion, will be populated with the data from the storage adapter.

_Note_: `find` gives two results to calling code: one immediately, and one later. `find` returns a record synchronously as it is called and calls back with a record, and importantly these two records are __not__ guaranteed to be the same instance. This is because batman.js maps the identities of incoming and outgoing records such that there is only ever one canonical instance representing a record, which is useful so bindings are always bound to the same thing. In practice, this means that calling code should use the record `find` calls back with if anything is going to bind to that object, which is most of the time. The returned record however remains useful for state inspection and bookkeeping.

    asyncTest '@find calls back the requested model if no error occurs', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'
        @persist AsyncTestStorageAdapter,
          storage:
            'posts2': {name: "Two", id:2}

      post = Post.find 2, (err, result) ->
        throw err if err
        post = result
      equal post.get('name'), undefined
      delay ->
        equal post.get('name'), "Two"

_Note_: `find` must be passed a callback function. This is for two reasons: calling code must be aware that `find`'s return value is not necessarily the canonical instance, and calling code must be able to handle errors.

    asyncTest '@find calls back with the error if an error occurs', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'
        @persist AsyncTestStorageAdapter

      error = false
      post = Post.find 3, (err, result) ->
        error = err
      delay ->
        ok error instanceof Error

## @load(options = {}, callback : Function)

`Model.load()` retrieves an array of records according to the given `options` from the storage adapter and calls back with an error if one occurred and the set of records if the operation was successful. `load` delegates to the storage adapter the `Model` has been `@persist`ed with, so it is up to the storage adapter's semantics to determine what the options do, what kind of errors may arise, and the timeline on which the callback may be called. The `callback` is a required function which should adopt the node style callback signature which accepts two arguments, an error, and the array of records. `load` returns undefined.

For the two main `StorageAdapter`s batman.js provides, the `options` do different things:

- For `Batman.LocalStorage`, `options` act as a filter. The adapter will scan all the records in `localStorage` and return only those records which match all the key/value pairs given in the options.
- For `Batman.RestStorage`, `options` are serialized into query parameters on the `GET` request.

It accepts a callback with two arguments: any error that occurred, and an array of loaded records.

    asyncTest '@load calls back an array of records retrieved from the storage adapter', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'
        @persist TestStorageAdapter,
          storage:
            'posts1': {name: "One", id:1}
            'posts2': {name: "Two", id:2}

      posts = false
      Post.load (err, result) ->
        throw err if err
        posts = result

      delay ->
        equal posts.length, 2
        equal posts[0].get('name'), "One"

    asyncTest '@load calls back with an empty array if no records are found', ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'
        @persist TestStorageAdapter, storage: []

      posts = false
      Post.load (err, result) ->
        throw err if err
        posts = result

      delay ->
        equal posts.length, 0

## @create(attributes = {}, callback) : Model

`App.Model.create` is a convenience method that is essentially equivalent to
calling `(new App.Model).save()`:

    asyncTest "@create instantiates a new record instance and saves it", ->
      class Post extends Batman.Model
        @resourceName: 'post'
        @encode 'name'
        @persist TestStorageAdapter, storage: []

      # Using new + save:
      record = new Post(name: 'aName')
      record.save()

      # Using create:
      otherRecord = Post.create name: 'aName', ->

      delay ->
        equal record.get('name'), otherRecord.get('name')
        equal record.isNew(), false
        equal otherRecord.isNew(), false

_Note_ : `attributes` is an empty object `{}` by default. This means the single-argument version of `create` accepts the callback, and not the attributes object.

## @findOrCreate(attributes = {}, callback) : Model

## @createFromJSON(attributes = {}) : Model

Returns an instance of the model based on `attributes`. If the `primaryKey` is present in `attributes`, the in-memory identity map will be searched for a match. If a match is found, it will be updated with `attributes` (without tracking) and returned. If the `primaryKey` isn't present, a new instance is added to the `loaded` set and returned.

Since `createFromJSON` checks the identity map, it's a great way to load data without duplicating records in memory.

## @createMultipleFromJSON(attributesArray: Array) : Array

Loads data from JSON like `Model.createFromJSON`, but `attributesArray` is an array of objects and returns an array of records. `createMultipleFromJSON` loads new records all at once, so `Model.loaded.itemsWereAdded` is only fired once.

## ::%id

A universally accessible accessor to the record's primary key. If the record's
primary key is `id` (the default), getting/setting this accessor simply passes
the call through to `id`, otherwise it proxies the call to the custom primary key.

    test "id proxies the primary key", ->
      class Post extends Batman.Model
        @primaryKey: 'name'

      post = new Post(name: 'Witty title')
      equal post.get('id'), 'Witty title'

      post.set('id', 'Wittier title')
      equal post.get('name'), 'Wittier title'

## ::isDirty() : Boolean

Returns `true` if any keys have been changed since the record was initialized or saved.

## ::%isDirty : Boolean

A bindable accessor on [`isDirty`](/docs/api/batman.model.html#prototype_function_isdirty).

## ::%dirtyKeys : Set

The [`Batman.Set`](/docs/api/batman.set.html) of keys which have been modified since the last time the record was saved.

## ::%errors : Batman.ErrorsSet

`errors` is a `Batman.ErrorsSet`, which is simply a [`Batman.Set`](/docs/api/batman.set.html) of [`Batman.ValidationError`](/docs/api/batman.validationerror.html)s present on the model instance.

- `user.get('errors')` returns the errors on the `user` record
- `user.get('errors.length')` returns the number of errors, total

You can also access the errors for a specific attribute of the record:

- `user.get('errors.email_address')` returns the errors on the `email_address` attribute
- `user.get('errors.email_address.length')` returns the number of errors on the `email_address` attribute

## ::constructor(idOrAttributes = {}) : Model

If `idOrAttributes` is an object, the values are mixed into the new record. Otherwise, `idOrAttrubutes` is set to the new record's [`id`](/docs/api/batman.model.html#prototype_accessor_id).

## ::isNew() : boolean

Returns true if the instance represents a record that hasn't yet been persisted to storage. The default implementation simply checks if `@get('id')` is undefined, but you can override this on your own models.

`isNew` is used to determine whether `record.save()` will perform a `create` action or a `save` action.

## ::%isNew : Boolean

A bindable accessor on [`isNew`](/docs/api/batman.model.html#prototype_function_isnew).

## updateAttributes(attributes) : Model

Mixes in `attributes` into the record (using `set`). Doesn't save the record.

## toString() : string

Returns a string representation suitable for debugging. By default this just contains the model's `resourceName` and `id`

## ::%attributes : Hash

`attributes` is a `Batman.Hash` where a record's attributes are stored. `Batman.Model`'s default accessor stores values in `attributes`, so it includes:

- attributes defined with `@encode`
- keys assigned with `set`, unless the key has a specifically defined accessor

But it doesn't include:

- keys that have specifically defined accessors (eg, `errors`, `lifecycle`, `isNew`)

A record's attributes are used by `Model::transaction` to create a deep copy of the record.

## ::toJSON() : Object

Returns a JavaScript object containing the attributes of the record, using any specified encoders.

    test "toJSON returns a JavaScript object with the record's attributes", ->
      class Criminal extends Batman.Model
        @encode "name", "notorious"

      criminal = new Criminal(name: "Talia al Ghul", notorious: true)
      criminal_json = criminal.toJSON()
      equal criminal_json.name, "Talia al Ghul"
      equal criminal_json.notorious, true

## ::fromJSON() : Model

Loads attributes from a bare object into this instance.

    test 'fromJSON overwrites existing attributes', ->
      class Criminal extends Batman.Model
        @encode "name", "notorious"

      criminal = new Criminal(name: "Dr. Jonathan Crane", notorious: false)
      new_params =
        name: "Scarecrow"
        notorious: true
      criminal.fromJSON(new_params)

      equal criminal.get("notorious"), true
      equal criminal.get("name"), "Scarecrow"

## ::toParam() : value

Returns a representation of the model suitable for use in a URL. By default, this is the record's `id`.

This method is used by the routing system for serializing records into a URL.

## ::hasStorage() : boolean

True when the record has a storage adapter defined.

## ::load(options = {}, callback)
`Load` tries to read the record from its storage adapter. The options object will be passed to the storage adapter when it performs the `read` operation. The callback takes three parameters: error, the loaded record, and the environment. `Load`ing a record clears all errors on that record.

If the read operation fails or if the record is in a state which doesn't permit `load`, (for example, calling `load` on a deleted record) the callback will be invoked with an error.

## ::save(options = {}, callback)
`Save` [validates](http://localhost:4000/docs/api/batman.model.html#prototype_function_validate) the record, and if it passes, fires the corresponding storage operation (defined by the `Batman.StorageAdapter` passed to  [`@persist`](/docs/api/batman.model.html#class_function_persist)). When the storage operation is complete, the callback is invoked with two parameters: any JavaScript error and the record.

If the record [`isNew`](/docs/api/batman.model.html#prototype_function_isnew), `save` performs a `create` operation. Otherwise, it performs a `save` operation.

If the record is not valid, the [validation errors](/docs/api/batman.validationerror.html) will be passed to the first parameter of the callback function and the storage operation will not be performed.

Available options include:
- `only`: A whitelist that will submit only the specified model attributes from the storage adapter.  This is useful when you want to do partial updates of a model without sending the full model content.  e.g., `options = {only: ['name', 'bio']}`
- `except`: A blacklist that will prevent specified model attributes from being transmitted from the storage adapter.  e.g., `options = {except: ['sensitive_data']}`

## ::destroy(options = {}, callback)

`Destroy` fires the corresponding storage operation. The callback takes three arguments: JavaScript Error, the record, and the environment. If the operation is successful, the record is removed from its Model's [`loaded`](/docs/api/batman.model.html#class_function_loaded) set.

```coffeescript
criminal = new Criminal name: "The penguin"
criminal.destroy (err, record, env) ->
  if err
    console.log "Oh no! #{record.get('name')} is still on the loose!"
```

If the record's current lifecycle state doesn't allow the `destroy` action, the callback will be invoked with a `Batman.StateMachine.InvalidTransitionError`. For example, this could occur if `destroy` is called on an already-destroyed record.

## ::validate(callback)

`Model::validate` checks the model against the validations declared in the model definition (with [`Model@validate`](/docs/api/batman.model.html#class_function_validate)). This method accepts a callback with two arguments: any JS error that occurred within the validator function, and the set of [`Batman.ValidationError`](/docs/api/batman.validationerror.html)s that the input generated.

For example:

    test "validate(callback) will call the callback only after all keys have been validated", ->
      class Product extends Batman.Model
        @validate 'name', 'price', presence: yes

      newProduct = new Product
      newProduct.validate (javascriptError, validationErrors) ->
        throw javascriptError if javascriptError
        equal validationErrors.length, 2
        equal newProduct.get('errors.length'), 2
        equal newProduct.get('errors.name.length'), 1
        equal newProduct.get('errors.price.length'), 1

## ::transaction() : Model

Creates a deep copy of the record instance based on its `"attributes"`, allowing it to be modified without affecting the original. Also mixes in `Batman.Transaction`.
Useful for implementing actions that can be cancelled.

To apply the changes made to a transaction, call `applyChanges`.
To apply changes and save the record after running validations, call `save`.

    test "transaction creates an independent clone of a record", ->
      record = new Batman.Model(name: 'Felix')

      transaction = record.transaction()
      transaction.set('name', 'Camouflage')
      equal transaction.get('name'), 'Camouflage'
      equal record.get('name'), 'Felix'

      transaction.applyChanges()
      equal record.get('name'), 'Camouflage'

## ::reflectOnAssociation(label : String)

Returns the `Batman.Association` for the record's association named by `label`.
Returns `null` if the association does not exist.

## ::reflectOnAllAssociations([type: String])

If `type` is passed (eg, `hasMany`), returns a `Batman.SimpleSet` of all associations of that type on the record.
If no type is passed, all associations are returned.
If the record has no associations, returns `null`.