Ember-data and MongoDB, how to handle _id - ruby-on-rails

Question

I'm using ember-data with rails and MongoDB and am having problem with the way IDs are stored in MongoDB - in a _id field.
Ember-data will use id as the default field for ID so I tried to override it like this:
App.User = DS.Model.extend
primaryKey: "_id"
name: DS.attr "string"
image: DS.attr "string"
This seems to work most of the time but in some instances I get exceptions from ember saying:
Uncaught Error: assertion failed: Your server returned a hash with the
key _id but you have no mappings
I suspect this might be a bug in ember-data because it's still heavily under development, but I was trying to find a way to get to map _id to id on the server side in rails? I'm using mongoid to do the mongo mapping.

Answer 1

If you are using Mongoid here is a solution that makes it so you don't have to add a method def id; object._id.to_s; end to every serializer
Add the following Rails initializer
Mongoid 3.x
module Moped
module BSON
class ObjectId
alias :to_json :to_s
alias :as_json :to_s
end
end
end
Mongoid 4
module BSON
class ObjectId
alias :to_json :to_s
alias :as_json :to_s
end
end
Active Model Serializer for Building
class BuildingSerializer < ActiveModel::Serializer
attributes :id, :name
end
Resulting JSON
{
"buildings": [
{"id":"5338f70741727450f8000000","name":"City Hall"},
{"id":"5338f70741727450f8010000","name":"Firestation"}
]
}
This is a monkey patch suggested by brentkirby and updated for Mongoid 4 by arthurnn

Answer 2

An other way could be to use (if possible for you) the ActiveModel::Serializer. (I think it should be close to rabl (?))
From the ember-data gihtub: https://github.com/emberjs/data:
Out of the box support for Rails apps that follow the active_model_serializers gem's conventions
When we began with ember-data we were crafting as_json(), but using the gem is definitely better :)

Answer 3

Ahh, instead of including _id in your JSON, you could craft the JSON to instead use the id method rather than the _id attribute. Ways:
You could use rabl, and the JSON could be like:
object #user
attributes :id, :email
node(:full_name) {|user| "#{user.first_name} #{user.last_name}"}
You could also craft the as_json method
class User
def as_json(args={})
super args.merge(:only => [:email], :methods => [:id, :full_name])
end
end

Answer 4

I had a similar problem using ember.js with ember-resource and couchdb, which also stores it's IDs as _id.
As solution to this problem I defined a superclass for all my model classes containing a computed property to duplicate _id into id like this:
// get over the fact that couchdb uses _id, ember-resource uses id
id: function(key, value) {
// map _id (couchdb) to id (ember)
if (arguments.length === 1) {
return this.get('_id');
}
else {
this.set('_id', value);
return value;
}
}.property('_id').cacheable()
Maybe this could solve your problem too?

Answer 5

The best way is to use ActiveModel::Serializers. Since we are using Mongoid, you will need to add an include statement like that (see this gist from benedikt):
# config/initializers/active_model_serializers.rb
Mongoid::Document.send(:include, ActiveModel::SerializerSupport)
Mongoid::Criteria.delegate(:active_model_serializer, :to => :to_a)
And then include your serializer. Something like that:
# app/serializers/user_serializer.rb
class UserSerializer < ActiveModel::Serializer
attributes :id, :name, :email
def id
object._id
end
end
This fixes the _id problem

Answer 6

The second part of joscas's answer fixed the id issue for me with Rails4/Ruby2 except I had to .to_s the _id.
class UserSerializer < ActiveModel::Serializer
attributes :id, :name, :email
def id
object._id.to_s
end
end

Answer 7

If you use Mongoid3, here is the monkey patch may work for you.
https://gist.github.com/4700909

Answer 8

I don't know exactly when this was added, but you can just tell Ember-Data that the primaryKey is _id:
DS.RESTAdapter.extend({
serializer: DS.RESTSerializer.extend({
primaryKey: '_id'
})
});

Answer 9

Although the question is quite old but i still think my answer could help others:
If you are using ActiveModelSerializer then you just need to do this :
class UserSerializer < ActiveModel::Serializer
attributes :id , :name
end
It works all fine. I am using emberjs on the front end btw.