如何在rails中追溯将主键添加到我的表中？

I've created a table without a primary key (:id => false), but now it has come back to bite my ass.

我创建了一个没有主键的表（：id => false），但现在又回来咬我的屁股了。

My app is already in production and I can't just drop it and recreate another one.

我的应用程序已经投入生产，我不能只删除它并重新创建另一个。

Is there a way to run a migration to add another auto increment primary key column to my table?

有没有办法运行迁移以向我的表添加另一个自动增量主键列？

4 个解决方案

#1

The command to add a primary key in a migration is:

在迁移中添加主键的命令是：

add_column :my_table, :id, :primary_key

add_column：my_table，：id，：primary_key

However, the wording of your question suggests that your table already has an auto-increment column. Unless I'm mistaken, there are several DBMS that do not allow more than one auto-increment column on a table.

但是，您的问题的措辞表明您的表已经有一个自动增量列。除非我弄错了，否则有几个DBMS不允许在表上使用多个自动增量列。

If you DO already have an auto-increment column and you actually want to use that column as your primary key, just add the following to your model:

如果您已经拥有自动增量列，并且实际上想要将该列用作主键，只需将以下内容添加到模型中：

set_primary_key "my_existing_column"

set_primary_key“my_existing_column”

Or in more recent versions of Rails:

或者在更新版本的Rails中：

self.primary_key = "my_existing_column"

self.primary_key =“my_existing_column”

In the case that you already have an auto-increment column and you can't use that as the primary key, you may be out of luck.

如果您已经有一个自动增量列，并且您不能将其用作主键，那么您可能会失败。

#2

If for some reason you created a table with a custom id field, but forgot to set id as the primary key, you need to run a migration to create the primary key constraint. The following was tested against a PostgreSQL database:

如果由于某种原因您创建了一个带有自定义ID字段的表，但忘记将id设置为主键，则需要运行迁移以创建主键约束。以下针对PostgreSQL数据库进行了测试：

class AddPrimaryKeyConstraintToFoobars < ActiveRecord::Migration
  def up
    execute "ALTER TABLE foobars ADD PRIMARY KEY (id);"
  end

  def down
    execute "ALTER TABLE foobars DROP CONSTRAINT foobars_pkey;"
  end
end

#3

I know in mySQl that you can add a column that has a default increment value. If you add that then each row will have a unique int value (and any new row will get a int value 1 greater then the last row added)

我知道在mySQl中你可以添加一个具有默认增量值的列。如果你添加它，那么每一行将具有唯一的int值（并且任何新行将获得比添加的最后一行更大的int值1）

You could add this column and set it as a primary key.

您可以添加此列并将其设置为主键。

#4

Was this a join table that now needs to become a real model with a primary key? If so, your best bet is to create the new table and copy the data into it.

这是一个现在需要成为具有主键的真实模型的连接表吗？如果是这样，最好的办法是创建新表并将数据复制到其中。

#1