如何回滚迁移？

-2

我已成功完成三次迁移。如何回滚迁移？

20150109133619_add_items.rb：

class AddItems < ActiveRecord::Migration 
    def change 
    create_table :pros do |t| 
     t.string :titlerr 
     t.text :description 
     t.string :image_url 
     t.decimal :price 

     t.timestamps 
    end 
    end 
end

20150109134955_add_col.rb：

class AddCol < ActiveRecord::Migration 
    def change 
    add_column :pros, :fieldname, :string 
    end 
end

20150109162301_del_col.rb：

class DelCol < ActiveRecord::Migration 
    def change 
    remove_column :pros, :fieldname 
    end 
end

现在我需要在迁移之前20150109134955.我回滚状态做了以下事情：

rake db:rollback

结果如下消息：

== DelCol: reverting ========================================================= 
rake aborted! 
StandardError: An error has occurred, this and all later migrations canceled: 

remove_column is only reversible if given a type./home/kalinin/.rvm/gems/ruby-2.0.0-p598/gems/activerecord-4.0.0/lib/active_record/migration/command_recorder.rb:128:in `invert_remove_column' 
/home/kalinin/.rvm/gems/ruby-2.0.0-p598/gems/activerecord-4.0.0/lib/active_record/migration/command_recorder.rb:66:in `inverse_of' 
........ 
........ 
........ 
/home/kalinin/.rvm/gems/ruby-2.0.0-p598/gems/activerecord-4.0.0/lib/active_record/railties/databases.rake:126:in `block (2 levels) in <top (required)>' 
Tasks: TOP => db:rollback 
(See full trace by running task with --trace)

我的第二次尝试：

rake db:rollback VERSION=20150109134955

结果如下消息：

== DelCol: reverting ========================================================= 
rake aborted! 
StandardError: An error has occurred, this and all later migrations canceled: 

remove_column is only reversible if given a type./home/kalinin/.rvm/gems/ruby-2.0.0-p598/gems/activerecord-4.0.0/lib/active_record/migration/command_recorder.rb:128:in `invert_remove_column' 
/home/kalinin/.rvm/gems/ruby-2.0.0-p598/gems/activerecord-4.0.0/lib/active_record/migration/command_recorder.rb:66:in `inverse_of' 
..... 
..... 
..... 
/home/kalinin/.rvm/gems/ruby-2.0.0-p598/gems/activerecord-4.0.0/lib/active_record/railties/databases.rake:126:in `block (2 levels) in <top (required)>' 
Tasks: TOP => db:rollback 
(See full trace by running task with --trace)

来源

2015-01-09 stackow6

你有没有尝试像20150109162301这样的错误信息建议添加'，：string'？那么发生了什么？ – 2015-01-09 20:31:18

请尝试运行'rake db：rollback -trace'并查看完整跟踪，并在此处发布跟踪。 – 2015-01-09 20:31:54

请阅读错误信息。它试图帮助你。 – ptd 2015-01-09 20:33:27

添加的数据类型为20150109162301_del_col .rb

class DelCol < ActiveRecord::Migration 
    def change 
    remove_column :pros, :fieldname, :string 
    end 
end

来源

2015-01-09 20:32:58 eabraham

如何回滚迁移？

回答

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