How to fill the related model on a many 2 many association?

Question

Using ember-data, I have this two models:

App.Post = DS.Model.extend
  title: DS.attr "string"
  body: DS.attr "string"
  categories: DS.hasMany "App.Category"

App.Category = DS.Model.extend
  name: DS.attr "string"
  posts: DS.hasMany 'App.Post'

and this serialization:

class PostSerializer < ActiveModel::Serializer
  attributes :id, :title, :body

  has_many :categories
  embed :ids, include: true
end

class CategorySerializer < ActiveModel::Serializer
  attributes :id, :name
end

When I ask for posts, I get the expected JSON and I can access a post's categories without problem, but if I request the categories (that I think that they are cached) I get the categories without any relation to posts. It doesn't even try to make a get request (that wouldn't work either).

So, shouldn't categories have their posts relations filled up?

Not sure if I miss something in ember or AMS (which I think that the category serializer should know that has many posts)

Answer 1

Well, after struggling with some guys at IRC I ended with this solution, which I hope it will be helpful for others and maybe improved.

The problem was that the categories doesn't had any post reference, So if you ask for Posts, you get the posts with categories, but the categories themselves knows nothing about posts.

If I try to do something like:

class CategorySerializer < ActiveModel::Serializer
  attributes :id, :name

  has_many :posts
  embed :ids, include: true
end

it will explode because they are referencing each other and you get a "Too deep level" or something like that.

You can do something like:

class CategorySerializer < ActiveModel::Serializer
  attributes :id, :name

  has_many :posts, embed: :objects
end

and it will work, but the result JSON will be huge because when you request posts, you get every post + every comment and inside them, every post that have that category... No love

So what's the idea? Having something like:

class PostSerializer < ActiveModel::Serializer
  attributes :id, :title, :body

  has_many :categories
  embed :ids, include: true
end

class CategorySerializer < ActiveModel::Serializer
  attributes :id, :name

  has_many :posts, embed: :ids
end

For every post you get the categories_ids and for every category you reference, you only get its attributes and the ids (not the entire objects) of the posts that belongs to that category.

But what happens when you go to '/#/categories' and you didn't loaded the posts yet? Well, since your CategorySerializer doesn't serialize any post, you won't get anything.

So since you can't do cross references between serializers, I ended with 4 serializers. 2 for posts and their categories and 2 for categories and their posts (so, doesn't matter if you load the posts first or the categories):

class PostSerializer < ActiveModel::Serializer
  attributes :id, :title, :body

  has_many :categories, serializer: CategoriesForPostSerializer
  embed :ids, include: true
end

class CategoriesForPostSerializer < ActiveModel::Serializer
  attributes :id, :name

  has_many :posts, embed: :ids
end

class CategorySerializer < ActiveModel::Serializer
  attributes :id, :name

  has_many :posts, serializer: PostsForCategorySerializer
  embed :ids, include: true
end

class PostsForCategorySerializer < ActiveModel::Serializer
  attributes :id, :title, :body

  has_many :categories, embed: :ids
end

This does the trick. But since I'm new with Ember and I'm not a crack of JSON design. If someones knows a simple way or maybe doing some embedded (always or load in the adapter, which I don't understand yet), please comment :)