Ruby on Rails Mysql2::Error: Table 'pages' 已经存在:CREATE TABLE `pages` 但不能迁移回来 [英] Ruby on Rails Mysql2::Error: Table 'pages' already exists: CREATE TABLE `pages` but cannot migrate back

问题描述

我试图运行迁移，但在第一次尝试运行时错过了 t.integer "subject_id" 中的一行.

I was trying to run a migration but had missed a line out of t.integer "subject_id" when first trying to run it.

迁移如下所示:

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

以上现在看起来是正确的，但是当我再次尝试运行它时，我得到了这个:

The above is now seemingly correct but when I try to run it again I get this:

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)

我知道这显然是在说您正在尝试创建一个名为 Pages 的表，该表已经存在，因为我搞砸的行是在创建表后立即出现的行.但是我无法弄清楚如何在表已经存在的情况下再次运行迁移.我试图注释掉创建表格的行，但这也不起作用.

I understand it is obviously saying you are trying to create a table called Pages which already exists as the line I messed up is the one immiediately after the table was created. But I cannot figure out how to have the migration run again with the table already existing. I have tried to comment out the line to create the table but that does not work either.

我还在做一个 Rails 初学者教程，所以上面是我唯一能想到的尝试.

I am still doing a beginners tutorial in Rails so the above is the only thing I could think of to try.

我现在尝试了 Shivam 的建议，但现在得到以下内容:

I have now tried Shivam's suggestion but now get the following:

== 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$ 

推荐答案

确保迁移文件与运行迁移期间的完全相同，然后像这样回滚迁移:

Make sure the migration file is exactly the same as it was during running the migration and then rollback the migration like this:

rake db:rollback STEP=1 # rollbacks 1 step

完成后，相应地编辑文件并:

Once that is done, edit the file accordingly and:

rake db:migrate 

或者您可以通过以下方式具体说明版本:

or you can specifically tell the version by:

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

或者

我可以看到您想要做的就是在模型表中添加一个新列 subject_id.您也可以通过运行独立迁移来实现此目的:>

I can see all you want to do is add a new column subject_id to you model table. You can achieve this by running a standalone migration too:

rails generate migration AddSubjectIdToPages subject_id:integer

紧随其后:

rake db:migrate

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