greetification greetification - 5 months ago 18
JSON Question

Serializing deeply nested associations with active_model_serializers

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 that 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.



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.

Answer

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.