Ruby-on-rails Rails：添加列后添加索引

Rails: Adding an index after adding column

提问by user1611830

Suppose I created a table tablein a Rails app. Some time later, I add a column running:

假设我table在 Rails 应用程序中创建了一个表。一段时间后，我添加一列运行：

rails generate migration AddUser_idColumnToTable user_id:string. 

Then I realize I need to add user_idas an index. I know about the add_indexmethod, but where should this method be called? Am I supposed to run a migration (if yes, which one ?), then adding by hand this method?

然后我意识到我需要添加user_id为索引。我知道这个add_index方法，但是这个方法应该在哪里调用？我是否应该运行迁移（如果是，是哪个？），然后手动添加此方法？

回答by Jaap Haagmans

You can run another migration, just for the index:

您可以运行另一个迁移，仅用于索引：

class AddIndexToTable < ActiveRecord::Migration
  def change
    add_index :table, :user_id
  end
end

回答by Vadym Tyemirov

If you need to create a user_idthen it would be a reasonable assumption that you are referencing a user table. In which case the migration shall be:

如果您需要创建一个，user_id那么可以合理地假设您正在引用一个用户表。在这种情况下，迁移应为：

rails generate migration AddUserRefToProducts user:references

This command will generate the following migration:

此命令将生成以下迁移：

class AddUserRefToProducts < ActiveRecord::Migration
  def change
    add_reference :user, :product, index: true
  end
end

After running rake db:migrateboth a user_idcolumn and an index will be added to the productstable.

运行后rake db:migrate既user_id列和索引将被添加到products表中。

In case you just need to add an index to an existing column, e.g. nameof a usertable, the following technique may be helpful:

如果你只需要一个索引添加到现有的塔，例如name一的user表，下面的技术可能会有所帮助：

rails generate migration AddIndexToUsers name:string:indexwill generate the following migration:

rails generate migration AddIndexToUsers name:string:index将生成以下迁移：

class AddIndexToUsers < ActiveRecord::Migration
  def change
    add_column :users, :name, :string
    add_index :users, :name
  end
end

Delete add_columnline and run the migration.

删除add_column行并运行迁移。

In the case described you could have issued rails generate migration AddIndexIdToTable index_id:integer:indexcommand and then delete add_columnline from the generated migration. But I'd rather recommended to undo the initial migration and add reference instead:

在所描述的情况下，您可以发出rails generate migration AddIndexIdToTable index_id:integer:index命令，然后add_column从生成的迁移中删除行。但我宁愿建议撤消初始迁移并添加引用：

rails generate migration RemoveUserIdFromProducts user_id:integer
rails generate migration AddUserRefToProducts user:references

回答by rdeandrade

Add in the generated migration after creating the column the following (example)

在创建列后在生成的迁移中添加以下内容（示例）

add_index :photographers, :email, :unique => true

回答by Mauro

For references you can call

如需参考，您可以致电

rails generate migration AddUserIdColumnToTable user:references

If in the future you need to add a general index you can launch this

如果将来您需要添加通用索引，您可以启动它

rails g migration AddOrdinationNumberToTable ordination_number:integer:index

Generate code:

生成代码：

class AddOrdinationNumberToTable < ActiveRecord::Migration
  def change
   add_column :tables, :ordination_number, :integer
   add_index :tables, :ordination_number, unique: true
  end
end

回答by vidur punj

You can use this, just think Job is the name of the model to which you are adding index cader_id:

您可以使用它，只需认为 Job 是您添加索引cader_id的模型的名称：

class AddCaderIdToJob < ActiveRecord::Migration[5.2]
  def change
    change_table :jobs do |t|
      t.integer :cader_id
      t.index :cader_id
    end
  end
end