在 Rails 迁移中向现有表添加列 [英] Adding a column to an existing table in a Rails migration

问题描述

我有一个需要 :email 列的用户模型(我忘记在初始脚手架期间添加该列).

I have a Users model which needs an :email column (I forgot to add that column during the initial scaffold).

我打开了迁移文件并添加了t.string :email，做了rake db:migrate，得到了一个NoMethodError.然后我添加了一行

I opened the migration file and added t.string :email, did rake db:migrate, and got a NoMethodError. Then I added the line

add_column :users, :email, :string

再次rake db:migrate，再次NoMethodError.我在这里错过了一步吗?

again rake db:migrate, again NoMethodError. Am I missing a step here?

这是迁移文件.

class CreateUsers < ActiveRecord::Migration  
  def self.up  
    add_column :users, :email, :string  
    create_table :users do |t|  
      t.string :username  
      t.string :email  
      t.string :crypted_password  
      t.string :password_salt  
      t.string :persistence_token  

      t.timestamps  
    end  
  end  

  def self.down  
    drop_table :users  
  end  
end

推荐答案

如果你已经运行了你的原始迁移(在编辑之前)，那么你需要生成一个新的迁移(rails generate migration add_email_to_users email:string 会解决问题).它将创建一个包含行的迁移文件:add_column :users, email, string然后执行 rake db:migrate 它将运行新迁移，创建新列.

If you have already run your original migration (before editing it), then you need to generate a new migration (rails generate migration add_email_to_users email:string will do the trick). It will create a migration file containing line: add_column :users, email, string Then do a rake db:migrate and it'll run the new migration, creating the new column.

如果您还没有运行原始迁移，您可以像尝试一样对其进行编辑.您的迁移代码几乎完美:您只需要完全删除 add_column 行(该代码试图在创建表之前向表中添加一列，并且您的表创建代码已经更新为包括 t.string :email.

If you have not yet run the original migration you can just edit it, like you're trying to do. Your migration code is almost perfect: you just need to remove the add_column line completely (that code is trying to add a column to a table, before the table has been created, and your table creation code has already been updated to include a t.string :email anyway).

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