Question

我已经将add_column：users，：confirmed_at（confirmation_at），：datetime命名为偶然。所以我将其更改为相应的字段名称：（confirmed_at）

然后我输入：rake db：在命令行中回滚。由于某种原因，它已被中止，但是首先我的Rails db迁移文件代码：

class AddConfirmableToDevise < ActiveRecord::Migration
  def up
    add_column :users, :confirmation_token, :string
    add_column :users, :confirmed_at, :datetime
    add_column :users, :confirmation_sent_at, :datetime

    add_index :users, :confirmation_token, unique: true
  end

  def down
    remove_column :users, :confirmation_token, :confirmed_at, :confirmation_sent_at
  end
end

迁移后出错：

tzurch:~/workspace (gravitar) $ rake db:migrate:redo

#the error that came up below
_________________________________________________
== 20160902201448 AddFullnameToUser: reverting ================================

-- remove_column(:users, :fullname, :string)

-> 0.0207s

== 20160902201448 AddFullnameToUser: reverted (0.0284s) =======================

== 20160902201448 AddFullnameToUser: migrating ================================

-- add_column(:users, :fullname, :string)

-> 0.0008s

== 20160902201448 AddFullnameToUser: migrated (0.0009s) =======================

== 20160913221959 AddConfirmableToDevise: migrating ===========================

-- add_column(:users, :confirmation_token, :string)

-> 0.0009s

-- add_column(:users, :confirmed_at, :datetime)

-> 0.0005s

-- add_column(:users, :confirmation_sent_at, :datetime)

rake aborted!

StandardError: An error has occurred, this and all later migrations canceled:

SQLite3::SQLException: duplicate column name: confirmation_sent_at: ALTER TABLE "users" ADD "confirmation_sent_at" datetime:

Answer 1

我想你在db

中已经有了这个表中的confirmation_sent_at字段

Answer 2

此处的问题是您用于删除列的语法是错误的。

正确的语法是remove_column

remove_column(table_name, column_name, type = nil, options = {})

使用

更改迁移

class AddConfirmableToDevise < ActiveRecord::Migration
  def up
    add_column :users, :confirmation_token, :string
    add_column :users, :confirmed_at, :datetime
    add_column :users, :confirmation_sent_at, :datetime

    add_index :users, :confirmation_token, unique: true
  end

  def down
    remove_column :users, :confirmation_token
    remove_column :users, :confirmed_at
    remove_column :users, :confirmation_sent_at

    remove_index :users, :confirmation_token
  end
end

或者完全删除down迁移并将up替换为change，rails会知道如何回滚：

class AddConfirmableToDevise < ActiveRecord::Migration
  def change
    add_column :users, :confirmation_token, :string
    add_column :users, :confirmed_at, :datetime
    add_column :users, :confirmation_sent_at, :datetime

    add_index :users, :confirmation_token, unique: true
  end
end

在第一次迁移后更改字段名称时，Rails db迁移中止错误

2 个答案: