ActiveModel 序列化器：运行时有条件吗？

我使用rails（5.0.1）和active_model_serializers（0.10.2）。我想以某种方式有条件地序列化has_many协会：

class Question < ApplicationRecord
    has_many :responses, :inverse_of => :question
end

class Response < ApplicationRecord
    belongs_to :question, :inverse_of => :responses
end

class QuestionSerializer < ActiveModel::Serializer
  attributes :id, :title, :created_at, :updated_at
  has_many :responses
end

class ResponseSerializer < ActiveModel::Serializer
  attributes :id, :title
end

我使用 jsonapi 并查询http://localhost:3000/api/questions/1我得到这样的回应：

响应1:

{
  "data": {
    "id": "1",
    "type": "questions",
    "attributes": {
      "title": "First",
      "created-at": "2017-02-14T09:49:20.148Z",
      "updated-at": "2017-02-14T13:55:37.365Z"
    },
    "relationships": {
      "responses": {
        "data": [
          {
            "id": "1",
            "type": "responses"
          }
        ]
      }
    }
  }
}

如果我删除has_many :responses from QuestionSerializer我明白了：

响应2:

{
  "data": {
    "id": "1",
    "type": "questions",
    "attributes": {
      "title": "First",
      "created-at": "2017-02-14T09:49:20.148Z",
      "updated-at": "2017-02-14T13:55:37.365Z"
    }
  }
}

我如何有条件的得到任一响应1 or 响应2在运行时？我尝试了找到的所有建议 - 都不适用于 AMS 0.10.2。目前，该条件仅以这种方式起作用：

class QuestionSerializer < ActiveModel::Serializer
  attributes :id, :title, :created_at, :updated_at
  has_many :responses if true
end

OR:

class QuestionSerializer < ActiveModel::Serializer
  attributes :id, :title, :created_at, :updated_at
  has_many :responses if false
end

在这两种情况下我真的得到了响应1 or 响应2。但这是硬编码的，我想将参数传递到序列化器中或做一些类似的事情。

我应该怎么办？

我想你已经回答了你自己的问题。如果你查看 AMS协会文件 https://github.com/rails-api/active_model_serializers/blob/v0.10.4/docs/general/serializers.md#associations它说支持条件。

据我所知，你只差一个错字

class QuestionSerializer < ActiveModel::Serializer
   has_many :responses, if: false
end

The attributes方法还支持if选项，如上所述here https://github.com/rails-api/active_model_serializers/blob/v0.10.4/docs/general/serializers.md#attributes.

你的是什么active_model_serializers版本？

EDIT： 我的回答也有错误。我在用着active_model_serializers (0.10.3)我能做到

class QuestionSerializer < ActiveModel::Serializer
   has_many :responses, if: -> { false }
end

The if选项适用于方法、过程或字符串。我认为您可以通过提供一个方法作为条件来在运行时做出决定。

class QuestionSerializer < ActiveModel::Serializer
  attr_writer :should_render_association
  has_many :responses, if: -> { should_render_association }
end
# Usage: 
serializer = QuestionSerializer.new(question)
serializer.should_render_association = false
serializer.to_json
# => no "responses" key