Rails: Serializing deeply nested associations with active_model_serializers

Question

I'm using Rails 4.2.1 and active_model_serializers 0.10.0.rc2

I'm new to API's and chose active_model_serializers because it seems to be becoming the standard for rails (Although I'm not opposed to using RABL or another serializer)

The problem I'm having is that I can't seem to include various attributes in multi-level relationships. For instance, I have:

Projects

class ProjectSerializer < ActiveModel::Serializer
  attributes                      :id, 
                                  :name,
                                  :updated_at

  has_many                        :estimates, include_nested_associations: true

end

and Estimates

class EstimateSerializer < ActiveModel::Serializer
  attributes                      :id, 
                                  :name, 
                                  :release_version, 
                                  :exchange_rate, 
                                  :updated_at,

                                  :project_id, 
                                  :project_code_id, 
                                  :tax_type_id 

  belongs_to                      :project
  belongs_to                      :project_code
  belongs_to                      :tax_type

  has_many                        :proposals

end

Proposals

class ProposalSerializer < ActiveModel::Serializer
  attributes                      :id, 
                                  :name, 
                                  :updated_at,

                                  :estimate_id

  belongs_to                      :estimate
end

When I hit the /projects/1 the above produces:

{
  "id": 1,
  "name": "123 Park Ave.",
  "updated_at": "2015-08-09T02:36:23.950Z",
  "estimates": [
    {
      "id": 1,
      "name": "E1",
      "release_version": "v1.0",
      "exchange_rate": "0.0",
      "updated_at": "2015-08-12T04:23:38.183Z",
      "project_id": 1,
      "project_code_id": 8,
      "tax_type_id": 1
    }
  ]
}

However, what I'd like it to produce is:

{
  "id": 1,
  "name": "123 Park Ave.",
  "updated_at": "2015-08-09T02:36:23.950Z",
  "estimates": [
    {
      "id": 1,
      "name": "E1",
      "release_version": "v1.0",
      "exchange_rate": "0.0",
      "updated_at": "2015-08-12T04:23:38.183Z",
      "project": { 
        "id": 1,
        "name": "123 Park Ave."
      },
      "project_code": {
        "id": 8,
        "valuation": 30
      },
      "tax_type": {
        "id": 1,
        "name": "no-tax"
      },
      "proposals": [
        {
          "id": 1,
          "name": "P1",
          "updated_at": "2015-08-12T04:23:38.183Z"
        },
        {
          "id": 2,
          "name": "P2",
          "updated_at": "2015-10-12T04:23:38.183Z"
        }
      ]
    }
  ]
}

Ideally, I'd also like to be able to specify which attributes, associations, and attributes of those associations are included in each serializer.

I've been looking through the AMS issues, and there does seem to be some back and forth on how this should be handled (or if this kind of functionality is even actually supported) but I'm having difficulty figuring out exactly what the current state is.

• https://github.com/rails-api/active_model_serializers/issues/835
• https://github.com/rails-api/active_model_serializers/issues/968
• https://github.com/rails-api/active_model_serializers/issues/414
• https://github.com/rails-api/active_model_serializers/issues/444

One of the proposed solutions was to override the attribute with a method to call the nested attributes, but that seems to be regarded as a hack so I wanted to avoid it if possible.

Anyway, an example of what of how to go about this or general API advice would be much appreciated.

Solution 1

So this my not be the best or even a good answer, but this is working how I need it to.

While including nested and side-loaded attributes appears to be supported when using the json_api adapter with AMS, I needed support for flat json. In addition, this method worked well because each serializer is specifically generating exactly what I need it to independent of any other serializer and without having to do anything in the controller.

Comments / alternate methods are always welcome.

Project Model

class Project < ActiveRecord::Base      
  has_many  :estimates, autosave: true, dependent: :destroy
end

ProjectsController

def index
  @projects = Project.all
  render json: @projects
end

ProjectSerializer

class ProjectSerializer < ActiveModel::Serializer
  attributes  :id, 
              :name,
              :updated_at,

              # has_many
              :estimates



  def estimates
    customized_estimates = []

    object.estimates.each do |estimate|
      # Assign object attributes (returns a hash)
      # ===========================================================
      custom_estimate = estimate.attributes


      # Custom nested and side-loaded attributes
      # ===========================================================
      # belongs_to
      custom_estimate[:project] = estimate.project.slice(:id, :name) # get only :id and :name for the project
      custom_estimate[:project_code] = estimate.project_code
      custom_estimate[:tax_type] = estimate.tax_type

      # has_many w/only specified attributes
      custom_estimate[:proposals] = estimate.proposals.collect{|proposal| proposal.slice(:id, :name, :updated_at)}

      # ===========================================================
      customized_estimates.push(custom_estimate)
    end

    return customized_estimates
  end
end

Result

[
  {
    "id": 1,
    "name": "123 Park Ave.",
    "updated_at": "2015-08-09T02:36:23.950Z",
    "estimates": [
      {
        "id": 1,
        "name": "E1",
        "release_version": "v1.0",
        "exchange_rate": "0.0",
        "created_at": "2015-08-12T04:23:38.183Z",
        "updated_at": "2015-08-12T04:23:38.183Z",
        "project": {
          "id": 1,
          "name": "123 Park Ave."
        },
        "project_code": {
          "id": 8,
          "valuation": 30,
          "created_at": "2015-08-09T18:02:42.079Z",
          "updated_at": "2015-08-09T18:02:42.079Z"
        },
        "tax_type": {
          "id": 1,
          "name": "No Tax",
          "created_at": "2015-08-09T18:02:42.079Z",
          "updated_at": "2015-08-09T18:02:42.079Z"
        },
        "proposals": [
          {
            "id": 1,
            "name": "P1",
            "updated_at": "2015-08-12T04:23:38.183Z"
          },
          {
            "id": 2,
            "name": "P2",
            "updated_at": "2015-10-12T04:23:38.183Z"
          }
        ]
      }
    ]
  }
]

I basically disregarded trying to implement any has_many or belongs_to associations in the serializers and just customized the behavior. I used slice to select specific attributes. Hopefully a more elegant solution will be forth coming.

Solution 2

Per commit 1426: https://github.com/rails-api/active_model_serializers/pull/1426 - and related discussion, you can see that the default nesting for json and attributes serialization is one level.

If you want deep nesting by default, you can set a configuration property in an active_model_serializer initializer:

ActiveModelSerializers.config.default_includes = '**'

For detailed reference from v0.10.6: https://github.com/rails-api/active_model_serializers/blob/v0.10.6/docs/general/adapters.md#include-option

Solution 3

If you are using the JSONAPI adapter you can do the following to render nested relationships:

render json: @project, include: ['estimates', 'estimates.project_code', 'estimates.tax_type', 'estimates.proposals']

You can read more from the jsonapi documentation:http://jsonapi.org/format/#fetching-includes

Solution 4

You can change default_includes for the ActiveModel::Serializer:

# config/initializers/active_model_serializer.rb
ActiveModel::Serializer.config.default_includes = '**' # (default '*')

In addition, in order to avoid infinite recursion, you can control the nested serialization follows:

class UserSerializer < ActiveModel::Serializer
  include Rails.application.routes.url_helpers

  attributes :id, :phone_number, :links, :current_team_id

  # Using serializer from app/serializers/profile_serializer.rb
  has_one :profile
  # Using serializer described below:
  # UserSerializer::TeamSerializer
  has_many :teams

  def links
    {
      self: user_path(object.id),
      api: api_v1_user_path(id: object.id, format: :json)
    }
  end

  def current_team_id
    object.teams&.first&.id
  end

  class TeamSerializer < ActiveModel::Serializer
    attributes :id, :name, :image_url, :user_id

    # Using serializer described below:
    # UserSerializer::TeamSerializer::GameSerializer
    has_many :games

    class GameSerializer < ActiveModel::Serializer
      attributes :id, :kind, :address, :date_at

      # Using serializer from app/serializers/gamers_serializer.rb
      has_many :gamers
    end
  end
end

Result:

{
   "user":{
      "id":1,
      "phone_number":"79202700000",
      "links":{
         "self":"/users/1",
         "api":"/api/v1/users/1.json"
      },
      "current_team_id":1,
      "profile":{
         "id":1,
         "name":"Alexander Kalinichev",
         "username":"Blackchestnut",
         "birthday_on":"1982-11-19",
         "avatar_url":null
      },
      "teams":[
         {
            "id":1,
            "name":"Agile Season",
            "image_url":null,
            "user_id":1,
            "games":[
               {
                  "id":13,
                  "kind":"training",
                  "address":"",
                  "date_at":"2016-12-21T10:05:00.000Z",
                  "gamers":[
                     {
                        "id":17,
                        "user_id":1,
                        "game_id":13,
                        "line":1,
                        "created_at":"2016-11-21T10:05:54.653Z",
                        "updated_at":"2016-11-21T10:05:54.653Z"
                     }
                  ]
               }
            ]
         }
      ]
   }
}

Solution 5

In my case I created a file called 'active_model_serializer.rb' placed at 'MyApp/config/initializers' with the following content:

ActiveModelSerializers.config.default_includes = '**'

Do not forget to restart the server:

$ rails s

View more solutions

Comments

[Eric Norcross]

Does this approach actually utilize active_model_serializers or is it just the default rails way of outputting JSON?

[Eric Norcross]

I guess my biggest issue with this method is it requires managing the code in two different files; the Controller and the Serializer. That's not to say it isn't the correct way of doing it; just that I find it more inconvenient.

[Mirror318]

What if you don't want deep nesting as the default, but you want it for one specific model? (And what if that specific model needs 2 or 3 levels of nesting?)

[BF4]

you can pass in '**' per action. Note, that it's a security issue. Better to be explicit what you want to include.

[BF4]

@greetification No, it uses a vestige of AMS that was left in Rails when it was reverted. See in Rails ActiveModel::Serializers::JSON and ActiveModel::Serialization

[BF4]

This is the best way to get 'nesting'.. though JSON:API actually flattens it.

[Todd]

While the most upvoted answer to this question is certainly the correct conventional way, its hard to get what you want when following AMS conventions. I too just write my own callbacks for displaying nested associations, and find the AMS convention too unwieldy. I find this to be the case for pretty much anything concerning Rails and nested associations - conventions are unwieldy, defer to plain ol' ruby.