在Ruby on Rails 3中创建FOREIGN KEY约束是什么？ [英] What creates the FOREIGN KEY constraint in Ruby on Rails 3?

问题描述

据我所知，默认情况下会创建 id 字段，同时也是： PRIMARY KEY（ id 。

外键怎么样？

code>商店和产品表以及下列关联：

<$ p $购物车：has_many：产品
产品：belongs_to：shop

在产品中也有：

$ p $ t $整数shop_id

这就是外键，还有：

  add_index（products，shop_id）
  

$ b $但是，如果我导出数据库，我只看到：

$ p $ key $ index_products_on_shop_id`（shop_id`）

我应该怎么做才能添加

 
 
 
 
 
 
 
 
 
 
 $ b $ p>？
解决方案 
您可以使用外国人 gem将外键添加到您的应用程序。要开始添加以下内容到您的 Gemfile  
  gemforeigner 
  
之后，您可以轻松地在迁移中添加外键，如下所示：
  add_foreign_key：products，：shops 
  
这会将 product.shop_id 添加到 shop.id 中。请参阅文档以获取更多选项，如不同名称的键或自引用表。
I understand that by default the id field is created and also: PRIMARY KEY (id).

How about the foreign key ?

I have Shops and Products tables and the following associations:
Shop:    has_many :products
Product: belongs_to :shop
In Product I have also:
t.integer "shop_id"
which is meant to be the foreign key, and also:
add_index("products", "shop_id")
However, if I export the database I see only: 
KEY `index_products_on_shop_id` (`shop_id`)
What should I do in order to add 
FOREIGN KEY (`shop_id`) REFERENCES Shop(`id`)
?
解决方案
You can use the foreigner gem for adding foreign keys to your application. To get started add the following to your Gemfile
gem "foreigner"
After that you can easily add foreign keys in your migration like so:
add_foreign_key :products, :shops
This would add a foreign from product.shop_id to shop.id. See the documentation for more options like differently named keys or self-referencing tables.

                        
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