Nested collection created as array instead of collection - backbone.js

Question

I am having some trouble when I create a new model form json, with nested attributes that should be parsed as a collection. Here I show how I get to the error:
(Any help appreciated)
1) I create a user like this
user = new App.Models.User( {"email":"tom#gmail.com","id":1,"user_cities_attributes":[{"city_id":431,"user_action":"to-visit","user_id":1}] }
2) and then I check in the console what happened, the collection did not get created. :S
user.get('user_cities')
> undefined # where is my collection?! :(
user.get('user_cities_attributes')
> [Object] # mmm weird...
If I try after to add a new model to the collection...
cities = new App.Collections.CitiesCollection()
cities.fetch()
userCity = new App.Models.UserCity( { user: user, city: cities.first(), user_action: "to-visit" } )
now everything seems to be fine... what happened????
user.get('user_cities')
> Backbone.Collection {length: 20, models: Array[20], _byId: Object, model: function, user: User…}
user.get('user_cities_attributes')
undefined
MODELS
class App.Models.User extends Backbone.RelationalModel
paramRoot: 'user'
urlRoot: 'users'
defaults:
name: null
class App.Models.UserCity extends Backbone.RelationalModel
paramRoot: 'user_city'
urlRoot: 'user_cities'
defaults:
user_action: null
relations: [{
type: Backbone.HasOne,
key: 'user',
relatedModel: 'App.Models.User',
collectionType: 'App.Collections.UsersCollection',
keySource: 'user_id',
includeInJSON: 'id',
reverseRelation: {
key: 'user_cities',
keySource: 'user_cities_attributes',
includeInJSON: 'id'
}
},
{
type: Backbone.HasOne,
key: 'city',
relatedModel: 'App.Models.City',
collectionType: 'App.Collections.CitiesCollection',
includeInJSON: 'id',
keySource: 'city_id',
reverseRelation: {
key: 'users',
includeInJSON: 'id'
}
}]
class App.Models.City extends Backbone.RelationalModel
paramRoot: 'city'
urlRoot: 'cities'
defaults:
name: null
relations: [{
type: Backbone.HasMany,
key: 'places',
relatedModel: 'App.Models.Place',
collectionType: 'App.Collections.PlacesCollection',
keySource: 'places_attributes',
# parse: true,
includeInJSON: 'id',
autoFetch: true,
reverseRelation: {
key: 'city',
includeInJSON: 'id'
}
# 'relatedModel' is automatically set to 'Zoo'; the 'relationType' to 'HasOne'.
}]

Answer 1

Look at the note about reverseRelation and using coffeescript (from: http://backbonerelational.org/#relations-reverseRelation):
Note that if you define a relation (plus a reverseRelation) on a
model, but don't actually create an instance of that model, it is
possible initializeRelations will never get called, and the
reverseRelation will not be initialized. This can happen when extend
has been overridden, or redefined as in CoffeeScript. See setup.
Then try using .setup as described here: http://backbonerelational.org/#RelationalModel-setup