Question

我充实了新的Rails应用程序＆amp;我是第一次使用Rails 4。脚手架有一个单一的名称＆＃34;为每个MVC定义的字段。

然后我创建了一个简单的迁移＆amp;第一个模特协会：

class Ability < ActiveRecord::Base
    belongs_to :player, class_name: "Player", foreign_key: "player_id"
end

class Player < ActiveRecord::Base
    has_many :abilities
end

控制台显示正确的字段。我可以保存东西：

> Ability.first
Ability Load (0.1ms)  SELECT  "abilities".* FROM "abilities"   ORDER BY "abilities"."id" ASC LIMIT 1
=> #<Ability id: 1, name: "Ability0", value: 50, created_at: "2014-07-31 16:41:59", updated_at: "2014-07-31 18:14:57", player_id: nil> 

> Player.first
Player Load (0.3ms)  SELECT  "players".* FROM "players"   ORDER BY "players"."id" ASC LIMIT 1
=> #<Player id: 1, name: "Player0", created_at: "2014-07-31 16:42:00", updated_at: "2014-07-31 16:42:00"> 

> Ability.first.player = Player.first
Ability Load (0.4ms)  SELECT  "abilities".* FROM "abilities"   ORDER BY "abilities"."id" ASC LIMIT 1
Player Load (0.2ms)  SELECT  "players".* FROM "players"   ORDER BY "players"."id" ASC LIMIT 1
=> #<Player id: 1, name: "Player0", created_at: "2014-07-31 16:42:00", updated_at: "2014-07-31 16:42:00"> 

> Ability.first.save!
Ability Load (0.4ms)  SELECT  "abilities".* FROM "abilities"   ORDER BY "abilities"."id" ASC LIMIT 1
(0.1ms)  begin transaction
(0.1ms)  commit transaction
=> true

但是保存并不想＆＃34;采取＆＃34;：

> Ability.first
Ability Load (0.4ms)  SELECT  "abilities".* FROM "abilities"   ORDER BY "abilities"."id" ASC LIMIT 1
=> #<Ability id: 1, name: "Ability0", value: 50, created_at: "2014-07-31 16:41:59", updated_at: "2014-07-31 18:14:57", player_id: nil>

我知道这是一件简单的事情，但我感到很沮丧。问题是什么？

Answer 1

您正在将player与Ability的实例相关联并保存完全不同的Ability 实例（没有关联的player）这就是为什么播放器没有与您的Ability实例映射的原因。

让我们完成以下步骤：

第1步

Ability.first.player = Player.first

在这里，您创建了一个Ability的匿名实例，该实例引用abilities表中的第一条记录，然后将其与players表中的第一条记录相关联。这都是 in-memory ，并且关联尚未保存在表格中。

第2步

Ability.first.save!

接下来，您将再次创建 Ability的新匿名实例，它指的是abilities表中的第一条记录。但它与步骤1中创建的实例无关。因此，当您进行防火保存时！在它上面，它不会保存任何东西，因为在这个例子中没有任何字段被更改。

你能做的是：

ability = Ability.first
ability.player = Player.first
ability.save!

在所有步骤中，您使用相同的实例进行更改。

被Rails 4协会错误困惑

1 个答案:

第1步

第2步