为什么我的 Rails 5 应用程序每条记录打印两次？

Question

这是一个 rails 管理应用程序，同时也是一个 API。当我调用 myroot/api/v1/users 我得到每条记录两次。

这是我的用户模型class:

class User < ActiveRecord::Base
  devise :database_authenticatable, :recoverable,
         :trackable, :validatable, :registerable,
         :omniauthable

  include DeviseTokenAuth::Concerns::User
  has_many :records
end

这是我的记录模型class:

class Record < ApplicationRecord
  belongs_to :user
  has_attached_file :audio,
                      :url => "/assets/:class/:id/:attachment/:style.:extension",
                      :path => ":rails_root/public/assets/records/:id/:style/:basename.:extension"
  validates_attachment_presence :audio
  validates_attachment_size :audio, :less_than => 3.megabytes
  validates_attachment_content_type :audio, :content_type => [ 'audio/mpeg',  'audio/mp3' ]

end

这是我的控制器用户 class:

class Api::UsersController < Api::ApiController
  before_action :set_user, only: [:show, :edit, :update, :destroy]

  def index
      # users = User.all
      # render json: users.to_json(except: [:id, :user_id, :email, :nickname])
      users = User.joins(:records)
       render json: users.to_json(only: [:id, :user_id, :email, :nickname], 
       include: {records: {only: [:record_id, :geolocation, :audio_file_name, :audio_content_type]}})
  end

  def show
      user = User.find(params[:id])
      render json: user.to_json(except: [:id, :user_id, :email, :nickname])
  end
end

这是 JSON 结果：

[
    {
        "id": 4,
        "nickname": null,
        "email": "ricardope@gmail.com",
        "records": [
            {
                "geolocation": "-12.0858307,-76.9795114,17",
                "audio_file_name": "StarCraft_2_-_Probe_Quotes.mp3",
                "audio_content_type": "audio/mpeg"
            },
            {
                "geolocation": "-12.0858307,-76.9795114,17",
                "audio_file_name": "StarCraft_2_-_Selendis_Quotes.mp3",
                "audio_content_type": "audio/mpeg"
            }
        ]
    },
    {
        "id": 4,
        "nickname": null,
        "email": "ricardope@gmail.com",
        "records": [
            {
                "geolocation": "-12.0858307,-76.9795114,17",
                "audio_file_name": "StarCraft_2_-_Probe_Quotes.mp3",
                "audio_content_type": "audio/mpeg"
            },
            {
                "geolocation": "-12.0858307,-76.9795114,17",
                "audio_file_name": "StarCraft_2_-_Selendis_Quotes.mp3",
                "audio_content_type": "audio/mpeg"
            }
        ]
    },
    {
        "id": 6,
        "nickname": null,
        "email": "gabriela@gmail.com",
        "records": [
            {
                "geolocation": "-12.0858307,-76.9795114,17",
                "audio_file_name": "StarCraft_2_-_Carrier_Quotes.mp3",
                "audio_content_type": "audio/mpeg"
            },
            {
                "geolocation": "-12.0858307,-76.9795114,17",
                "audio_file_name": "StarCraft_2_-_Zealot_Quotes.mp3",
                "audio_content_type": "audio/mpeg"
            }
        ]
    },
    {
        "id": 6,
        "nickname": null,
        "email": "gabriela@gmail.com",
        "records": [
            {
                "geolocation": "-12.0858307,-76.9795114,17",
                "audio_file_name": "StarCraft_2_-_Carrier_Quotes.mp3",
                "audio_content_type": "audio/mpeg"
            },
            {
                "geolocation": "-12.0858307,-76.9795114,17",
                "audio_file_name": "StarCraft_2_-_Zealot_Quotes.mp3",
                "audio_content_type": "audio/mpeg"
            }
        ]
    }
]

这是日志：

Processing by Api::UsersController#index as */*
  User Load (0.2ms)  SELECT `users`.* FROM `users` INNER JOIN `records` ON `records`.`user_id` = `users`.`id`
  Record Load (0.2ms)  SELECT `records`.* FROM `records` WHERE `records`.`user_id` = 4
  CACHE Record Load (0.0ms)  SELECT `records`.* FROM `records` WHERE `records`.`user_id` = 4  [["user_id", 4]]
  Record Load (0.3ms)  SELECT `records`.* FROM `records` WHERE `records`.`user_id` = 6
  CACHE Record Load (0.0ms)  SELECT `records`.* FROM `records` WHERE `records`.`user_id` = 6  [["user_id", 6]]
Completed 200 OK in 97ms (Views: 0.3ms | ActiveRecord: 3.4ms)

Answer 1

正如 Pavan 所说，我更改了 users = User.joins(:records) for users = User.all 或 User.includes(:records) 并起作用了。

Answer 2

说明

users = User.joins(:records)

上面的活动记录查询触发 users 和 records table 之间的 INNER JOIN 查询。这意味着它将从两个 table 中获取所有记录，因为没有 where 子句。

输出将是来自 users table 或 records table 的总行数，哪个最高。

这就是您获得 users table.

重复记录的原因

这一行User.all只给你userstable行的记录，如果你还想要recordstable行那么你必须按照下面。

现在下面的行为您提供 users table 的结果以及来自 records table

的所有相关记录

User.includes(:records)

您不会看到来自 users table 的重复记录。因为它将在 2 table 秒上查询，一个在 users 上查询，另一个在 records

上查询

希望你能通过这篇post得到更多的说明。

为什么我的 Rails 5 应用程序每条记录打印两次？

Why does my Rails 5 application print twice each record?

ruby-on-rails

ruby

rails-activerecord

ruby-on-rails-5

rails-api