anchor.diff:  * +COLLECTION_PER_ASSOCIATION+ stores the association in a dedicated MongoDB collection per association
   hibernate.ogm.mongodb.write_concern::
   Defines the write concern setting to be applied when issuing writes against the MongoDB datastore.
  -Possible settings are (values of the +com.mongodb.WriteConcern+ enum): +ERRORS_IGNORED+, +ACKNOWLEDGED+, +UNACKNOWLEDGED+,
  -+FSYNCED+, +JOURNALED+, +NONE+, +NORMAL+, +SAFE+, +MAJORITY+, +FSYNC_SAFE+,
  -+JOURNAL_SAFE+, +REPLICAS_SAFE+.
  +Possible settings are (values of the +WriteConcernType+ enum):
  ++ERRORS_IGNORED+, +ACKNOWLEDGED+, +UNACKNOWLEDGED+, +FSYNCED+, +JOURNALED+, +REPLICA_ACKNOWLEDGED+, +MAJORITY+ and +CUSTOM+.
  +When set to +CUSTOM+, a custom +WriteConcern+ implementation type is to be specified.
  +hibernate.ogm.mongodb.write_concern_type::
  +Specifies a custom +WriteConcern+ implementation type (fully-qualified name, class object or instance).
  +This is useful in cases where the pre-defined configurations are not sufficient,
  +e.g. if you want to ensure that writes are propagated to a specific number of replicas or given "tag set".
  +Only takes affect if +hibernate.ogm.mongodb.write_concern+ is set to +CUSTOM+.
  +
   For more information, please refer to the
   http://api.mongodb.org/java/current/com/mongodb/WriteConcern.html[official documentation].
   This option is case insensitive and the default value is +ACKNOWLEDGED+.
  
positive.code: [source, JAVA]
  ----
  @Entity
  @AssociationStorage(AssociationStorageType.ASSOCIATION_DOCUMENT)
  @AssociationDocumentStorage(AssociationDocumentType.COLLECTION_PER_ASSOCIATION)
  public class Zoo {
  
negative.code:     @Override
      public void configure(Configurable configurable) {
          configurable.configureOptionsFor( MongoDB.class )
              .writeConcern( WriteConcernType.REPLICA_ACKNOWLEDGED )
              .entity( Zoo.class )
                  .associationStorage( AssociationStorageType.ASSOCIATION_DOCUMENT )
                  .associationDocumentStorage( AssociationDocumentType.COLLECTION_PER_ASSOCIATION )
                  .property( "animals", ElementType.FIELD )
                      .associationStorage( AssociationStorageType.IN_ENTITY )
              .entity( Animal.class )
                  .writeConcern( new RequiringReplicaCountOf( 3 ) )
                  .associationStorage( AssociationStorageType.ASSOCIATION_DOCUMENT );
      }
  }
  