Rails 5：添加belongs_to关联

Question

我有两个表“ users”和“ friendships”，我试图建立一种关系，以便一个用户可以与其他用户建立友谊，因此使用rails g model Friendship user:references friend:references status生成此模型友谊rails g model Friendship user:references friend:references status

在Friendship.rb模型中：

class Friendship < ApplicationRecord
  belongs_to :user
  belongs_to :friend,class_name: "User"
end

但是在创建记录时，它显示了以下错误：

Friendship.create(user_id: 1, friend_id:2, id: 1)

   (0.1ms)  begin transaction
  User Load (0.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 1], ["LIMIT", 1]]
  User Load (0.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 2], ["LIMIT", 1]]
  SQL (0.4ms)  INSERT INTO "friendships" ("id", "user_id", "friend_id", "created_at", "updated_at") VALUES (?, ?, ?, ?, ?)  [["id", 1], ["user_id", 1], ["friend_id", 2], ["created_at", "2018-02-26 19:39:57.865042"], ["updated_at", "2018-02-26 19:39:57.865042"]]
   (0.1ms)  rollback transaction
Traceback (most recent call last):
        1: from (irb):2
ActiveRecord::StatementInvalid (SQLite3::SQLException: no such table: main.friends: INSERT INTO "friendships" ("id", "user_id", "friend_id", "created_at", "updated_at") VALUES (?, ?, ?, ?, ?))
irb(main):003:0> 

会是什么呢？ 我有Rails 5.1.5

Answer 1

您的友谊模型已正确设置，但迁移可能未正确。 它看起来应该像这样：

class CreateFriendships < ActiveRecord::Migration[5.1]
  def change
    create_table :friendships do |t|
      t.references :user, index: true, foreign_key: true
      t.references :friend, index: true, foreign_key: { to_table: :users }
    end
  end
end

我已经在一个新的Rails 5.1.5项目中进行了设置，它正在为我工​​作：

>> User.create(name: 'First User')
>> User.create(name: 'Second User')
>> Friendship.create(user_id: 1, friend_id:2, id: 1)
   (0.1ms)  begin transaction
  User Load (0.7ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 1], ["LIMIT", 1]]
  User Load (0.1ms)  SELECT  "users".* FROM "users" WHERE "users"."id" = ? LIMIT ?  [["id", 2], ["LIMIT", 1]]
  SQL (0.8ms)  INSERT INTO "friendships" ("id", "user_id", "friend_id") VALUES (?, ?, ?)  [["id", 1], ["user_id", 1], ["friend_id", 2]]
   (0.8ms)  commit transaction
#<Friendship id: 1, user_id: 1, friend_id: 2>

顺便说一句，您应避免将ID号分配给非持久对象。 最好让数据库处理该工作。 我将简单地创建一个友谊：

>> Friendship.create(user_id: 1, friend_id: 2)