Rails的HAS_ONE与类名和外键 [英] Rails has_one with class name and foreign key

问题描述

我有一个Rails的模式，我用两个 HAS_ONE 关系：请求和朋友。当在控制台中使用：

  F = FriendRequest.all
F [0] .requester
 

我得到的ActiveRecord :: StatementInvalid：SQLite3的::的SQLException：没有这样的列：users.requester_id：选择用户*从用户WHERE用户，requester_id= 4限制。 1 。

我真的不知道如何指定一个类名和密钥，指定备案`HAS_ONE的关系。这是我的模型：

 类FriendRequest＆LT;的ActiveRecord :: Base的
  HAS_ONE：请求者：将class_name =＆GT; 用户，：foreign_key =＆GT; requester_id
  HAS_ONE：朋友：将class_name =＆GT; 用户，：foreign_key =＆GT; friend_id
结束
 

我怎么能这样做呢？在 belongs_to的关系，我用的是相同的，显然是将 HAS_ONE 与 belongs_to的。谢谢！

解决方案

  HAS_ONE：请求者：将class_name =＆GT; 用户，：foreign_key =＆GT; requester_id
 

该行（从您发布的code）表示请求是用户，和表用户应包含一列 requester_id 是对 friend_requests 记录。铁轨错误消息指出该列 requester_id 不存在（你必须通过的迁移）。

在这种情况下，使用

 导轨产生迁移AddRequesterIdToUsers requester_id：整数
 

这将产生迁移：

 类AddRequesterIdToUsers＆LT; ActiveRecord的::迁移
  高清变化
    add_column：用户：requester_id，整数
  结束
结束
 

和运行他们迁移耙分贝：迁移

看href="http://guides.rubyonrails.org/association_basics.html"> Rails的关系指南上的 HAS_ONE 和 belongs_to的，以及如何使用它们。

I have a Rails model which I use two has_one relations: requesterand friend. When in the console I use:

f = FriendRequest.all
f[0].requester

I get ActiveRecord::StatementInvalid: SQLite3::SQLException: no such column: users.requester_id: SELECT "users".* FROM "users" WHERE "users"."requester_id" = 4 LIMIT 1 .

I don't really know how to specify a `has_one' relationship with a class name and a key which specifies the record. This is my model:

class FriendRequest < ActiveRecord::Base
  has_one :requester, :class_name => "User", :foreign_key => "requester_id"
  has_one :friend, :class_name => "User", :foreign_key => "friend_id"
end

How could I do it? In a belongs_to relationship I use the same, obviously replacing has_onewith belongs_to. Thanks!

解决方案

has_one :requester, :class_name => "User", :foreign_key => "requester_id"

This line (from the code that you posted) indicates that the requester is a User, and the table users should contain a column requester_id that is the foreign key toward friend_requests records. The rails error message states that the column requester_id does not exists (you have to create it via a migration).

In this case, use

rails generate migration AddRequesterIdToUsers requester_id:integer

It will generate the migration:

class AddRequesterIdToUsers < ActiveRecord::Migration
  def change
    add_column :users, :requester_id, :integer
  end
end  

And run them migration with rake db:migrate.

Look at the Rails Relation Guide for more information on differences between has_one and belongs_to, and how to use them.

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