Question

I’m attempting use the REST API in my rails (version 3.2.9) app.

I am POSTing a json packet to a standard rails scaffolded controller, which includes details for the model itself, and nested children.

The parent model and its children are successfully inserted into the database. However, the response from the POST doubles the nested children.

Why are the nested associations being doubled in the POST response? I have been trying to get this right for the last few days… it is driving me nuts.

Specific examples

JSON request

POST http://localhost:3000/audio_events HTTP/1.1
Host: localhost:3000
Connection: keep-alive
Content-Length: 432
Accept: application/json, text/plain, */*

{
    "audio_event": {
        "start_time_seconds": 0.05,
        "end_time_seconds": 15.23,
        "low_frequency_hertz": 1000,
        "high_frequency_hertz": 8753,
        "audio_event_tags_attributes": [
            {
                "tag_id": "-1"
            },
            {
                "tag_id": "-2"
            }
        ],
        "audio_recording_id": "1bd0d668-1471-4396-adc3-09ccd8fe949a"
    }
}

JSON response

HTTP/1.1 201 Created
Location: http://localhost:3000/audio_events/27
Content-Type: application/json; charset=utf-8
X-Ua-Compatible: IE=Edge
Etag: "c79ccdf981a9fadad3a8b08c3a878e8e"
Cache-Control: max-age=0, private, must-revalidate
Content-Length: 924
Server: WEBrick/1.3.1 (Ruby/1.9.3/2012-04-20)
Date: Mon, 26 Nov 2012 00:27:47 GMT
Connection: Keep-Alive

{
    "created_at": "2012-11-26T00:27:32Z",
    "creator_id": 1,
    "deleted_at": null,
    "deleter_id": null,
    "end_time_seconds": "15.23",
    "high_frequency_hertz": "8753.0",
    "id": 27,
    "is_reference": false,
    "low_frequency_hertz": "1000.0",
    "start_time_seconds": "0.05",
    "updated_at": "2012-11-26T00:27:32Z",
    "updater_id": 1,
    "audio_event_tags": [
        {
            "audio_event_id": 27,
            "created_at": "2012-11-26T00:27:32Z",
            "creator_id": 1,
            "tag_id": -1,
            "updated_at": "2012-11-26T00:27:32Z",
            "updater_id": 1
        },
        {
            "audio_event_id": 27,
            "created_at": "2012-11-26T00:27:32Z",
            "creator_id": 1,
            "tag_id": -2,
            "updated_at": "2012-11-26T00:27:32Z",
            "updater_id": 1
        },
        // DUPLICATES ARE HERE
        {
            "audio_event_id": 27,
            "created_at": "2012-11-26T00:27:32Z",
            "creator_id": 1,
            "tag_id": -1,
            "updated_at": "2012-11-26T00:27:32Z",
            "updater_id": 1
        },
        {
            "audio_event_id": 27,
            "created_at": "2012-11-26T00:27:32Z",
            "creator_id": 1,
            "tag_id": -2,
            "updated_at": "2012-11-26T00:27:32Z",
            "updater_id": 1
        }
    ],
    "audio_recording": {
        "id": 1,
        "uuid": "1bd0d668-1471-4396-adc3-09ccd8fe949a"
    }
}

Models

Many to many model

class AudioEventTag < ActiveRecord::Base
  belongs_to :audio_event
  belongs_to :tag
  accepts_nested_attributes_for :audio_event

  attr_accessible :audio_event, :tag, :tag_id

  stampable
  belongs_to :user, :class_name => 'User', :foreign_key => :creator_id

  validates_uniqueness_of :audio_event_id, :scope => :tag_id
end

The tag model

class Tag < ActiveRecord::Base
  has_many :audio_event_tags
  has_many :audio_events, :through => :audio_event_tags
  accepts_nested_attributes_for :audio_events, :audio_event_tags

  attr_accessible :is_taxanomic, :text, :type_of_tag

  stampable
  belongs_to :user, :class_name => 'User', :foreign_key => :creator_id
  acts_as_paranoid
  validates_as_paranoid
end

The audio event model

class AudioEvent < ActiveRecord::Base
  belongs_to :audio_recording

  has_many :tags, :through => :audio_event_tags, :uniq => true

  has_many :audio_event_tags
  accepts_nested_attributes_for :audio_event_tags

  attr_accessible :audio_recording_id, :end_time_seconds, :high_frequency_hertz, :is_reference,
                  :low_frequency_hertz, :start_time_seconds,
                  :tags_attributes, :audio_event_tags_attributes

  stampable
  belongs_to :user, :class_name => 'User', :foreign_key => :creator_id
  acts_as_paranoid
  validates_as_paranoid

  # validation
  validates :audio_recording, :presence => true

  validates :start_time_seconds, :presence => true, :numericality => { :greater_than_or_equal_to  => 0 }
  validates :end_time_seconds, :numericality => { :greater_than_or_equal_to  => 0 }

  validates :low_frequency_hertz, :presence => true, :numericality => { :greater_than_or_equal_to  => 0 }
  validates :high_frequency_hertz,  :numericality => { :greater_than_or_equal_to  => 0 }

  # json formatting
  def as_json(options={})
    super(
        :include =>
            [
                :audio_event_tags,
                :audio_recording  => {:only => [:id, :uuid]}
            ],
        :except => :audio_recording_id
    )
  end
end

Updates

As requested in comments, the code for my action in the controller

# POST /audio_events
# POST /audio_events.json
def create
  @audio_event = AudioEvent.new(params[:audio_event])
  #@audio_event.audio_event_tags.each{ |aet|  aet.build() }

  #@audio_event.audio_event_tags.count.times { @audio_event.audio_event_tags.build }

  respond_to do |format|
    if @audio_event.save

      format.json { render json: @audio_event, status: :created, location: @audio_event }
    else
      format.json { render json: @audio_event.errors, status: :unprocessable_entity }
    end
  end
end

And, I tried removing the stampable and acts_as_paranoid macros to no effect.

Updates 2

If I try adding 3 nested attributes, I get 6 back. 4 gives back 8, and 5 gives back 10.

Answer 1

Reposting from comments.

Looks like the json serialization issue. If separate get is working you could try @audio_event.audio_event_tags.reload before format.json in the controller.

—
It is certainly strange. Inmemory details for audio_event_tags got messed up at @audio_event.save line. Does AudioEvent have after_save callbacks?. If there are no callbacks then I don’t know how that can happen. Need to reproduce it. It is a serious problem to deal with if it happens for all nested attributes.