Relational layer over modal for Backbone. Can manage single id or multiple id relations between models. one-to-one, one-to-many, many-to-many, smart selection of id key, or possible to specify it ('through' keyword). Autofetch can also fetch missing related collection models.

gistfile1.coffee

###
# Adding relation support to models

Note: Given collections were here Singletons in this project, you can also use instances of collections instead.

relations:
  friends: require 'collections/Users' # @get('friends') will return an array of friend if friends_ids or friends_id is an array
  store: require 'collections/Store' # @get('store') will return the store object if there is a store_id
  subcategories:
    through: 'category_ids'
    collection: require 'collections/Categories'
  customer:
    collection: require 'collections/Customers'
    autofetch: true # will fetch it, and if found will trigger the 'change' event of the model

For relation items, a callback can be passed: `@get 'customer', (customer)-> #do something`,
it's mainly usefull when autofetch is enabled, the callback will be triggered once the object
has been retrieved from the server.

If it's a collection like `subcategories` in the above exemple, the callback will be triggered once all objects will be retrieved.
###

BaseModel extends Backbone.Model
  get: (name, cb)->
    # Nothing special to do if no relations have been defined for this key
    return super unless r = @relations?[name]

    # Retrieve id or ids of model(s) to return, and define collection
    ids = (r.through and @get r.through) or @get(name + '_id') or @get(name + '_ids')
    collection = r.collection or r

    # Ensure that _ids is always an array
    _ids = [].concat ids
    
    after_cb = unless cb then (->) else _.after _ids.count, cb

    models = []
    for id in _ids
      # fetch model if not found and autofetch option is enabled
      model = collection.get id
      if r.autofetch and not model
        model = new collection.model id: id
        model.fetch success: =>
          @trigger 'change'
          after_cb models
        collection.add model
        models.push model
      else
        models.push model
        after_cb models

    if typeof ids isnt 'Array' then models[0] else models