在Rails 4中添加引用列迁移

小鱼儿 2023-03-04 05:25 6阅读 0赞

本文翻译自：[Add a reference column migration in Rails 4][]

*A user has many uploads.* **用户有很多上传。** *I want to add a column to the `uploads` table that references the `user` .* **我想在`uploads`表中添加一个引用该`user` 。** *What should the migration look like?* **迁移应该是什么样的？**

*Here is what I have.* **这就是我所拥有的。** *I'm not sure if I should use (1) `:user_id, :int` or (2) `:user, :references` .* **我不确定是否应该使用（1） `:user_id, :int`或（2） `:user, :references` 。** *I'm not even sure if (2) works.* **我甚至不确定（2）是否有效。** *Just trying to do this the "rails" way.* **只是试图以“轨道”的方式做到这一点。**

class AddUserToUploads < ActiveRecord::Migration
      def change
        add_column :uploads, :user_id, :integer
      end
    end

*Relevant question except for Rails 3. [Rails 3 migrations: Adding reference column?][Rails 3 migrations_ Adding reference column]* **除Rails之外的相关问题3. [Rails 3迁移：添加引用列？][Rails 3 migrations_ Adding reference column]**

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参考：[https://stackoom.com/question/1xJe1/在Rails-中添加引用列迁移][https_stackoom.com_question_1xJe1_Rails-]

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***Rails 4.x*** **Rails 4.x**

*When you **already have** `users` and `uploads` tables and wish to **add a new relationship** between them.* **当您已经拥有 `users`并`uploads`表格并希望在它们之间添加新关系时 。**

*All you need to do is: just generate a migration using the following command:* **您需要做的就是：只需使用以下命令生成迁移：**

rails g migration AddUserToUploads user:references

*Which will create a migration file as:* **这将创建一个迁移文件：**

class AddUserToUploads < ActiveRecord::Migration
      def change
        add_reference :uploads, :user, index: true
      end
    end

*Then, run the migration using `rake db:migrate` .* **然后，使用`rake db:migrate`运行`rake db:migrate` 。** *This migration will take care of adding a new column named `user_id` to `uploads` table (referencing `id` column in `users` table), PLUS it will also add an index on the new column.* **此迁移将负责添加名为`user_id`的新列到`uploads`表（引用`users`表中的`id`列），PLUS它还将在新列上添加索引。**

***UPDATE \[For Rails 4.2\]*** **更新\[For Rails 4.2\]**

*Rails can't be trusted to maintain referential integrity;* **不能信任Rails来维护引用完整性;** *relational databases come to our rescue here.* ***关系数据库*来到我们这里救援。** *What that means is that we can add foreign key constraints at the database level itself and ensure that database would reject any operation that violates this set referential integrity.* **这意味着我们可以在*数据库级别*自己添加外键约束，并确保数据库拒绝任何违反此set参照完整性的操作。** *As @infoget commented, **Rails 4.2** ships with native support for foreign keys(referential integrity) .* **正如@infoget所评论的那样， Rails 4.2附带了*对外键的*本机支持*（参照完整性）* 。** *It's not required but you might want to add foreign key(as it's very useful) to the reference that we created above.* **这不是必需的，但您可能希望将外键（因为它非常有用）添加到我们上面创建的引用中。**

*To add foreign key to an existing reference , create a new migration to add a foreign key:* **要将外键添加到*现有引用* ，请创建新迁移以添加外键：**

class AddForeignKeyToUploads < ActiveRecord::Migration
      def change
        add_foreign_key :uploads, :users
      end
    end

*To create a completely brand new reference with a foreign key(in Rails 4.2) , generate a migration using the following command:* **要*使用外键*创建完全*全新的引用（在Rails 4.2中）* ，请使用以下命令生成迁移：**

rails g migration AddUserToUploads user:references

*which will create a migration file as:* **这将创建一个迁移文件：**

class AddUserToUploads < ActiveRecord::Migration
      def change
        add_reference :uploads, :user, index: true
        add_foreign_key :uploads, :users
      end
    end

*This will add a new foreign key to the `user_id` column of the `uploads` table.* **这将向`uploads`表的`user_id`列添加新的外键。** *The key references the `id` column in `users` table.* **该键引用`users`表中的`id`列。**

***NOTE:** This is in addition to adding a reference so you still need to **create a reference first then foreign key** ( you can choose to create a foreign key in the same migration or a separate migration file ).* **注意：这是添加引用的补充，因此您仍然需要先创建引用然后创建外键 （ *您可以选择在同一迁移中创建外键或单独的迁移文件* ）。** *Active Record only supports single column foreign keys and currently only `mysql` , `mysql2` and `PostgreSQL` adapters are supported.* **Active Record仅支持单列外键，目前仅支持`mysql` ， `mysql2`和`PostgreSQL`适配器。** *Don't try this with other adapters like `sqlite3` , etc. Refer to [Rails Guides: Foreign Keys][Rails Guides_ Foreign Keys] for your reference.* **不要尝试使用`sqlite3`等其他适配器。请参阅[Rails指南：外键][Rails Guides_ Foreign Keys]供您参考。**

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## *Rails 5* **Rails 5** ##

*You can still use this command to create the migration:* **您仍然可以使用此命令创建迁移：**

rails g migration AddUserToUploads user:references

*The migration looks a bit different to before, but still works:* **迁移看起来与以前有点不同，但仍然有效：**

class AddUserToUploads < ActiveRecord::Migration[5.0]
      def change
        add_reference :uploads, :user, foreign_key: true
      end
    end

*Note that it's `:user` , not `:user_id`* **请注意，它是`:user` ，not `:user_id`**

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做同样事情的另一种语法是：

rails g migration AddUserToUpload user:belongs_to

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***\[Using Rails 5\]*** **\[使用Rails 5\]**

*Generate migration:* **生成迁移：**

rails generate migration add_user_reference_to_uploads user:references

*This will create the migration file:* **这将创建迁移文件：**

class AddUserReferenceToUploads < ActiveRecord::Migration[5.1]
      def change
        add_reference :uploads, :user, foreign_key: true
      end
    end

*Now if you observe the schema file, you will see that the uploads table contains a new field.* **现在，如果您观察架构文件，您将看到uploads表包含一个新字段。** *Something like: `t.bigint "user_id"` or `t.integer "user_id"` .* **类似于： `t.bigint "user_id"`或`t.integer "user_id"` 。**

*Migrate database:* **迁移数据库：**

rails db:migrate

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*if you like another alternate approach with `up` and `down` method try this:* **如果你喜欢另一种替代方法有`up`和`down`的方法试试这个：**

def up
        change_table :uploads do |t|
          t.references :user, index: true
        end
      end
    
      def down
        change_table :uploads do |t|
          t.remove_references :user, index: true
        end
      end

[Add a reference column migration in Rails 4]: https://oldbug.net/q/1xJe1/Add-a-reference-column-migration-in-Rails-4
[Rails 3 migrations_ Adding reference column]: https://stackoverflow.com/questions/4954969/rails-3-migrations-adding-reference-column
[https_stackoom.com_question_1xJe1_Rails-]: https://stackoom.com/question/1xJe1/%E5%9C%A8Rails-%E4%B8%AD%E6%B7%BB%E5%8A%A0%E5%BC%95%E7%94%A8%E5%88%97%E8%BF%81%E7%A7%BB
[Rails Guides_ Foreign Keys]: http://edgeguides.rubyonrails.org/active_record_migrations.html#foreign-keys