How do you initialize an ActiveModel::Serializer class with an ActiveRecord::Relation array?

问题

I have a serializer

class FundingSerializer < ActiveModel::Serializer
  attributes :id, 

  has_one :user
  has_one :tournament
  embed :ids, include: true
end

That initializes with the proper associations

FundingSerializer.new(Funding.first).to_json

yields

"{\"users\":[{\"id\":2,\"first_name\":\"Nick\"}],\"tournaments\":[{\"id\":1,\"end_date\":\"2013-07-21T23:18:54.981Z\",\"start_date\":\"2013-07-14T23:18:54.980Z\"}],\"funding\":{\"id\":1}}"

but,

FundingSerializer.new(Funding.all).to_json

gets this error.

undefined method `read_attribute_for_serialization' for #<ActiveRecord::Relation::ActiveRecord_Relation_Funding:0x007f998910a250>
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/activerecord-4.0.0/lib/active_record/relation/delegation.rb:121:in `method_missing'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/activerecord-4.0.0/lib/active_record/relation/delegation.rb:68:in `method_missing'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/active_model_serializers-0.8.1/lib/active_model/serializer.rb:99:in `block in attribute'
    from (eval):3:in `_fast_attributes'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/active_model_serializers-0.8.1/lib/active_model/serializer.rb:466:in `rescue in attributes'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/active_model_serializers-0.8.1/lib/active_model/serializer.rb:454:in `attributes'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/active_model_serializers-0.8.1/lib/active_model/serializer.rb:478:in `_serializable_hash'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/active_model_serializers-0.8.1/lib/active_model/serializer.rb:360:in `serializable_hash'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/active_model_serializers-0.8.1/lib/active_model/serializer.rb:344:in `as_json'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/activesupport-4.0.0/lib/active_support/json/encoding.rb:50:in `block in encode'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/activesupport-4.0.0/lib/active_support/json/encoding.rb:81:in `check_for_circular_references'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/activesupport-4.0.0/lib/active_support/json/encoding.rb:49:in `encode'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/activesupport-4.0.0/lib/active_support/json/encoding.rb:34:in `encode'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/activesupport-4.0.0/lib/active_support/core_ext/object/to_json.rb:16:in `to_json'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/active_model_serializers-0.8.1/lib/active_model/serializer.rb:333:in `to_json'
    from (irb):1
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/railties-4.0.0/lib/rails/commands/console.rb:90:in `start'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/railties-4.0.0/lib/rails/commands/console.rb:9:in `start'
    from /Users/nicholasshook/.rvm/gems/ruby-2.0.0-p247@pokerfund/gems/railties-4.0.0/lib/rails/commands.rb:64:in `<top (required)>'

I do not want to simply render json: Funding.all because I would like to pass this json around to other objects in my rails application and with an angularjs app. Thanks,

回答1:

Now you can do that in this way (using AMS v0.10.2):

ActiveModel::Serializer.serializer_for(Funding.all).to_json

EDIT (03.03.2017)
This method is not working anymore. Use aNoble's answer:

ActiveModelSerializers::SerializableResource.new(Funding.all).to_json

回答2:

I think this is what you're looking for:

ActiveModel::ArraySerializer.new(Funding.all, each_serializer: FundingSerializer).to_json

See this Thoughtbot blog post for an example.

回答3:

I'm not sure if this is an idiomatic solution, but it should work:

Funding.all.map{|f| FundingSerializer.new(f)}.to_json

回答4:

This worked for me in version 0.10.2:

ActiveModelSerializers::SerializableResource.new(Funding.all, each_serializer: FundingSerializer).to_json

回答5:

You can explicitly provide the collection serializer as well.

render json: Funding.all, serializer: ActiveModel::ArraySerializer, each_serializer: FundingSerializer

回答6:

Looks like they are adjusting this again in the newest ActiveModel::Serializers gem version. You no longer can call to_json on the ArraySerializer (which is not ActiveModel::Serializer::ArraySerializer).

Here's what I did to get around it.

let(:resource)        { Funding.all }
let(:serializer)      { ActiveModel::Serializer::ArraySerializer.new(resource, each_serializer: FundingSerializer)
let(:serialization)   { ActiveModel::Serializer::Adapter.create(serializer) }
subject               { JSON.parse(serialization.to_json) }

Calling subject will get you the json you are after.

Here are a couple of more resources which dive into testing setup for further reading: http://eclips3.net/2015/01/24/testing-active-model-serializer-with-rspec/ https://robots.thoughtbot.com/validating-json-schemas-with-an-rspec-matcher

回答7:

Testing the response for active_model_serializers with version >= 0.10.0 I've done this simple helper for RSpec:

module AMSHelper
  def ams_array_serializer(collection, options: {}, adapter: :json)
    serializer = ActiveModel::Serializer::ArraySerializer.new(collection)
    adapter_class = ActiveModel::Serializer::Adapter.adapter_class(adapter)
    adapter_class.new(serializer, options)
  end

  def ams_serializer(object, options: {}, adapter: :json)
    serializer = ActiveModel::Serializer.serializer_for(object).new(object)
    adapter_class = ActiveModel::Serializer::Adapter.adapter_class(adapter)

    adapter_class.new(serializer, options)
  end
end

RSpec.configure do |config|
  config.include AMSHelper, type: :request
end

So you can simply test with:

RSpec.describe "Posts", type: :request do
  describe "GET /" do
    it "returns http success" do
      get posts_path
      expect(response_body).to eq(ams_array_serializer(Post.all).to_json)
    end
  end
end

I hope this could be useful for someone.

回答8:

assume you have a serializer class(Foo) not match your resources name(Bar), I use following approach to easily serialize objects:

class BaseSerializer < ActiveModel::Serializer
  def self.collection_serialize(resources)
    ActiveModelSerializers::SerializableResource.new(resources, each_serializer: self)
  end
end

let Foo serializer inherit BaseSerializer:

class FooSerializer < BaseSerializer
  ...
end

use FooSerializer in controller or outside:

bar = Bar.all
FooSerializer.collection_serialize(bar).to_json

来源：https://stackoverflow.com/questions/17542793/how-do-you-initialize-an-activemodelserializer-class-with-an-activerecordrel