序列化一对多关联的最后一条记录

Question

我有一个用户在 Height 模型中记录了许多高度（身高测量值），但想仅序列化最后一个高度。

我试图创建一个（假的）自定义 has_one 关联，但它没有给我我想要的东西......

app/serializers/user_serializer.rb

class UserSerializer < BaseSerializer
  attributes :email

  # has_many :heights
  has_one :current_height, record_type: :height do |user|
    user.heights.last
  end
end

app/controllers/users_controller.rb

options[:include] = [:heights]
render json: UserSerializer.new(user, options).

按原样，我得到了错误："heights is not specified as a relationship on UserSerializer."

如果我取消注释 # has_many :heights，我会得到：

{
    "data": {
        "id": "1",
        "type": "user",
        "attributes": {
            "email": "fake@email.com"
        },
        "relationships": {
            "heights": {
                "data": [
                    {
                        "id": "1",
                        "type": "height"
                    },
                    {
                        "id": "2",
                        "type": "height"
                    }
                ]
            },
            "currentHeight": {
                "data": {
                    "id": "2",
                    "type": "height"
                }
            }
        }
    },
    "included": [
        {
            "id": "1",
            "type": "height",
            "attributes": {
                "value": "186.0"
            }
        },
        {
            "id": "2",
            "type": "height",
            "attributes": {
                "value": "187.0"
            }
        }
    ]
}

但我不想在复合文档中包含所有记录的高度...

预期结果

{
    "data": {
        "id": "1",
        "type": "user",
        "attributes": {
            "email": "fake@email.com"
        },
        "relationships": {
            "currentHeight": {
                "data": {
                    "id": "2",
                    "type": "height"
                }
            }
        }
    },
    "included": [
        {
            "id": "2",
            "type": "height",
            "attributes": {
                "value": "187.0"
            }
        }
    ]
}

Answer 1

如果我指责你想多了，请原谅我，但你不能给你的用户添加一个方法来获得最后一个高度吗？

class User < ApplicationRecord
  #
  # your user code here
  # ...

  def last_height
    self.heights.last
  end
end

然后用current_user.last_height获取记录

如果这不是您的要求，我很抱歉，我可能没有完全理解这个问题。

Answer 2

您可以将此添加到User 模型

has_one :last_height, -> { order 'created_at DESC' }, class_name: "Height"