Rails 4 DB Migration Error: undefined method `to_sym' for nil:NilClass

Question

我对 rails 比较陌生，正在编写应用程序。到目前为止，该应用程序本身运行良好。最近我想迁移这样的东西：(更新)

class ChangeStuffFromTools < ActiveRecord::Migration
  def change
    change_column :tools, :shares, :integer, :default => 0
    change_column :tools, :views, :integer, :default => 0
    change_column :tools, :likes, :integer, :default => 0
    change_column :tools, :favorites, :integer, :default => 0
    change_column :tools, :featured, :boolean, :default => false
  end
end

我收到这个错误：

$ rails g migration remove_stuff_from_tools
      invoke  active_record
      create    db/migrate/20160904090608_remove_stuff_from_tools.rb

Jonas@JONAS_PC ~/gitapps/ocubit (master)
$ rake db:migrate
== 20160904090608 RemoveStuffFromTools: migrating =============================
-- remove_column(:tools, :featured, :boolean)
rake aborted!
StandardError: An error has occurred, this and all later migrations canceled:

undefined method `to_sym' for nil:NilClass
c:/Users/Jonas/gitapps/ocubit/db/migrate/20160904090608_remove_stuff_from_tools.rb:3:in
change'
      c:inmigrate' NoMethodError: undefined method to_sym' for nil:NilClass
      c:/Users/Jonas/gitapps/ocubit/db/migrate/20160904090608_remove_stuff_from_tools.rb:3:in
  change' c:in `migrate' Tasks: TOP => db:migrate (See full trace by running task with --trace)

我怎么可能修复它，我的意思是我需要以某种方式访问​​我的数据库来编辑它:)

Answer 1

remove_column 的语法是：

remove_column table_name, feild name

所以尝试：

class RemoveStuffFromTools < ActiveRecord::Migration
  def change
    remove_column :tools, :featured
    remove_column :tools, :shares
    remove_column :tools, :views
    remove_column :tools, :likes
    remove_column :tools, :favorites
  end
end

更新：

不支持 sqlite remove_column，对于简单的开发数据库，​​您可以：

1. 更新原来的 create_table_migration 并删除不需要的列。

2. 重新创建您的数据库：rake db:drop 然后 rake db:create 最后 rake db:migrate

Answer 2

如果需要更改列的默认值或空值，也可以使用以下方法：

change_column_default(:accounts, :authorized, 1)
change_column_null(:users, :nickname, false)

欲了解更多信息，here are more migration methods