Question

我试图进行迁移，但在第一次尝试运行时错过了t.integer“subject_id”的一行。

迁移看起来像这样：

class CreatePages < ActiveRecord::Migration

  def up
    create_table :pages do |t|
      t.integer "subject_id"
        # same as: t.references :subject
        t.string "name"
        t.string "permalink"
        t.integer "position"
        t.boolean "visible", :default => false
        t.timestamps
    end
    add_index("pages", "subject_id")
    add_index("pages", "permalink")
  end

  def down
    drop_table :pages
  end

end

以上现在似乎是正确的，但当我再次尝试再次运行时，我得到了这个：

George$ rake db:migrate
== 20150110112705 CreatePages: migrating ======================================
-- create_table(:pages)
rake aborted!
StandardError: An error has occurred, all later migrations canceled:

Mysql2::Error: Table 'pages' already exists: CREATE TABLE `pages` (`id` int(11) auto_increment PRIMARY KEY, `subject_id` int(11), `name` varchar(255), `permalink` varchar(255), `position` int(11), `visible` tinyint(1) DEFAULT 0, `created_at` datetime, `updated_at` datetime) ENGINE=InnoDB/Users/George/Sites/simple_cms/db/migrate/20150110112705_create_pages.rb:4:in `up'
ActiveRecord::StatementInvalid: Mysql2::Error: Table 'pages' already exists: CREATE TABLE `pages` (`id` int(11) auto_increment PRIMARY KEY, `subject_id` int(11), `name` varchar(255), `permalink` varchar(255), `position` int(11), `visible` tinyint(1) DEFAULT 0, `created_at` datetime, `updated_at` datetime) ENGINE=InnoDB
/Users/George/Sites/simple_cms/db/migrate/20150110112705_create_pages.rb:4:in `up'
Mysql2::Error: Table 'pages' already exists
/Users/George/Sites/simple_cms/db/migrate/20150110112705_create_pages.rb:4:in `up'
Tasks: TOP => db:migrate
(See full trace by running task with --trace)

我明白这显然是在说你正在尝试创建一个名为Pages的表，这个表已经存在，因为我搞砸的行是在创建表之后立即执行的行。但我无法弄清楚如何使用已存在的表再次运行迁移。我试图注释掉该行以创建表格，但这也不起作用。

我还在Rails做一个初学者教程，所以上面是我唯一能想到的尝试。

编辑：我现在尝试了Shivam的建议，但现在得到以下内容：

== 20150110112657 CreateSubjects: reverting ===================================
-- drop_table(:subjectsend)
rake aborted!
StandardError: An error has occurred, all later migrations canceled:

Mysql2::Error: Unknown table 'simple_cms_development.subjectsend': DROP TABLE `subjectsend`/Users/George/Sites/simple_cms/db/migrate/20150110112657_create_subjects.rb:13:in `down'
ActiveRecord::StatementInvalid: Mysql2::Error: Unknown table 'simple_cms_development.subjectsend': DROP TABLE `subjectsend`
/Users/George/Sites/simple_cms/db/migrate/20150110112657_create_subjects.rb:13:in `down'
Mysql2::Error: Unknown table 'simple_cms_development.subjectsend'
/Users/George/Sites/simple_cms/db/migrate/20150110112657_create_subjects.rb:13:in `down'
Tasks: TOP => db:rollback
(See full trace by running task with --trace)
George$

Answer 1

确保迁移文件与运行迁移期间的迁移文件完全相同，然后像这样回滚迁移：

rake db:rollback STEP=1 # rollbacks 1 step

完成后，相应地编辑文件并执行：

rake db:migrate

或者您可以通过以下方式具体说明该版本：

rake db:migrate VERSION=20141222070950 #verison is timestamp from your migration filename

<强>替代地

我可以看到你要做的就是在模型表中添加一个新列subject_id。您也可以通过运行standalone migration来实现此目的：

rails generate migration AddSubjectIdToPages subject_id:integer

接下来是：

rake db:migrate

Ruby on Rails Mysql2 ::错误：表＆＃39;页面＆＃39;已存在：CREATE TABLE`page`但无法迁移回来

1 个答案: