Question

这是我的迁移文件：

class AddSeoMetaInfoToArticles < ActiveRecord::Migration
  def self.up
    add_column :articles, :seo_title, :string, { :default => "", :null => false }
    add_column :articles, :seo_description, :string, { :default => "", :null => false }
    add_column :articles, :seo_keywords, :string, :string, { :default => "", :null => false }
  end

  def self.down
    remove_column :articles, :seo_keywords
    remove_column :articles, :seo_description
    remove_column :articles, :seo_title
  end
end

当我尝试运行'rake db：migrate'时，我收到以下错误

$ rake db:migrate
AddSeoMetaInfoToArticles: migrating =======================================
-- add_column(:articles, :seo_title, :string, {:default=>"", :null=>false})
   -> 0.0341s
-- add_column(:articles, :seo_description, :string, {:default=>"", :null=>false})
   -> 0.0100s
-- add_column(:articles, :seo_keywords, :string, :string, {:default=>"", :null=>false})
rake aborted!
An error has occurred, this and all later migrations canceled:

wrong number of arguments (5 for 4)

Tasks: TOP => db:migrate
(See full trace by running task with --trace)

我对rails很新，我不确定我做错了什么。这是Rails 3.0.9，如果有所不同，还有Postgres数据库。

Answer 1

add_column :articles, :seo_keywords, :string, :string, { :default => "", :null => false }

有:string两次，所以最终会传递5个参数而不是4。

您可能还想考虑使用change编写迁移 - 您的迁移等同于

class AddSeoMetaInfoToArticles < ActiveRecord::Migration
  def change
    change_table :articles do |t|
      t.string :seo_title, :default => "", :null => false
      t.string :seo_description, :default => "", :null => false
      t.string :seo_keywords, :default => "", :null => false
    end
  end
end

我觉得眼睛更容易。它还有一个优点，你可以传递：bulk =＆gt; true为change_table，它将所有3列添加组合成1个alter table语句，这通常要快得多。

这两种方式当然都有效。

Answer 2

您在此行中提供两次:string参数：

    add_column :articles, :seo_keywords, :string, :string, { :default => "", :null => false }

rake db：migrate error错误的参数个数（5个为4）

2 个答案: