如何在Rails迁移中将一列（包含内容）移动到另一个表？ [英] How do I move a column (with contents) to another table in a Rails migration?

问题描述

我需要将一些列从一个现有表移动到另一个表。

I need to move some columns from one existing table to another. How do I do it using a rails migration?

class AddPropertyToUser < ActiveRecord::Migration
  def self.up
    add_column :users, :someprop, :string
    remove_column :profiles, :someprop
  end

  def self.down
    add_column :profiles, :someprop, :string
    remove_column :users, :someprop
  end
end

上面只是创建新列，但值保留为空...

The above just creates the new columns, but values are left empty...

我要避免记录

如果可以通过编程方式移动列值，性能特征是什么？它会逐行执行，还是可以批量更新？

If there is a way to move column values programmatically, what are the performance characteristics? Would it do row-by-row, or is there a way to update in bulk?

推荐答案

我最终使用了这种迁移（经过测试，它可以正常工作，并成功回滚）：

I ended up using this migration (tested, it works, and rolls back successfully):

class AddPropertyToUser < ActiveRecord::Migration
  def self.up
    add_column :users, :someprop, :string
    execute "UPDATE users u, profiles p SET u.someprop = p.someprop WHERE u.id = p.user_id"
    remove_column :profiles, :someprop
  end

  def self.down
    add_column :profiles, :someprop, :string
    execute "UPDATE profiles p, users u SET p.someprop = u.someprop WHERE p.user_id = u.id"
    remove_column :users, :someprop
  end
end

我喜欢它，因为它避免了大型数据库上的逐行更新。

I like it because it avoids the row-by-row updates on a large database.

这篇关于如何在Rails迁移中将一列（包含内容）移动到另一个表？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！