Rails 4 DB 迁移错误：nil:NilClass 的未定义方法“to_sym”

Question

我对 Rails 比较陌生，并且正在编写应用程序。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

我收到此错误：

$ 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，我的意思是我需要访问我的数据库来编辑它:)

Answer 1

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

Answer 2

remove_column 的语法是：

remove_column table_name, feild name

那就试试吧：

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：

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

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

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