如何永久忽略ActiveRecord :: Base类中的数据库列？

Question

我有一个遗留数据库,我正在尝试使用Rails进行建模.其中一个表有一个名为列的列attributes,我认为这是Rails保留的名称.

这是表的SQL:

CREATE TABLE `album` (
  `id` int(11) NOT NULL,
  `artist` int(11) NOT NULL,
  `name` varchar(255) NOT NULL,
  `gid` char(36) NOT NULL,
  `modpending` int(11) DEFAULT '0',
  `attributes` int(11) DEFAULT '0',
  ...
);

这是我的ActiveRecord类:

class Album < ActiveRecord::Base
  set_table_name "album"
  belongs_to :artist
  has_many :tracks, :through => :album_tracks
end

这是我尝试实例化实例时发生的事情:

hornairs@bishop:~/Sites/logdb (master *)$ rails c
Loading development environment (Rails 3.0.3)
no such file to load -- irbtools
ruby-1.9.2-p0 > x = Album.find_by_name("Champ")
 => #<Album id: 969139, artist: 354493, name: "Champ", gid: "15a9a4b8-9dd9-4f6f-b4e9-7c69948af88f", modpending: 0, attributes: 1100, page: 143735328, language: 120, script: 28, modpending_lang: nil, quality: -1, modpending_qual: 0> 
ruby-1.9.2-p0 > x.name
ActiveRecord::DangerousAttributeError: attributes_before_type_cast is defined by ActiveRecord
  from /Users/hornairs/.rvm/gems/ruby-1.9.2-p0@logdb/gems/activerecord-3.0.3/lib/active_record/attribute_methods.rb:23:in `instance_method_already_implemented?'
  from /Users/hornairs/.rvm/gems/ruby-1.9.2-p0@logdb/gems/activemodel-3.0.3/lib/active_model/attribute_methods.rb:263:in `block (2 levels) in define_attribute_methods'
  from /Users/hornairs/.rvm/gems/ruby-1.9.2-p0@logdb/gems/activemodel-3.0.3/lib/active_model/attribute_methods.rb:262:in `each'
  from /Users/hornairs/.rvm/gems/ruby-1.9.2-p0@logdb/gems/activemodel-3.0.3/lib/active_model/attribute_methods.rb:262:in `block in define_attribute_methods'
  from /Users/hornairs/.rvm/gems/ruby-1.9.2-p0@logdb/gems/activemodel-3.0.3/lib/active_model/attribute_methods.rb:261:in `each'
  from /Users/hornairs/.rvm/gems/ruby-1.9.2-p0@logdb/gems/activemodel-3.0.3/lib/active_model/attribute_methods.rb:261:in `define_attribute_methods'
  from /Users/hornairs/.rvm/gems/ruby-1.9.2-p0@logdb/gems/activerecord-3.0.3/lib/active_record/attribute_methods.rb:13:in `define_attribute_methods'
  from /Users/hornairs/.rvm/gems/ruby-1.9.2-p0@logdb/gems/activerecord-3.0.3/lib/active_record/attribute_methods.rb:41:in `method_missing'
  from /Users/hornairs/.rvm/gems/ruby-1.9.2-p0@logdb/gems/thwart-0.0.4/lib/thwart/canable.rb:27:in `method_missing'
  from (irb):2
  from /Users/hornairs/.rvm/gems/ruby-1.9.2-p0@logdb/gems/railties-3.0.3/lib/rails/commands/console.rb:44:in `start'
  from /Users/hornairs/.rvm/gems/ruby-1.9.2-p0@logdb/gems/railties-3.0.3/lib/rails/commands/console.rb:8:in `start'
  from /Users/hornairs/.rvm/gems/ruby-1.9.2-p0@logdb/gems/railties-3.0.3/lib/rails/commands.rb:23:in `<top (required)>'
  from script/rails:6:in `require'
  from script/rails:6:in `<main>'
ruby-1.9.2-p0 > 

看起来好像attributes名称是保留的,所以我想找到一些方法来忽略所有查询,并在反映模式来定义模型类时让AR忽略它.有什么建议？谢谢!

Answer 1

使用罗宾链接和其他一些SO答案的组合解决了这个问题

class Album < ActiveRecord::Base
  set_table_name "album"

  class << self
    def instance_method_already_implemented?(method_name)
      return true if method_name =~ /^attributes/
      super
    end
  end

  belongs_to :artist
  has_many :tracks, :through => :album_tracks
end

诀窍.我使用了一个大的彻底更改来返回true而不会为所有方法开始抛出错误attributes,我不认为它在其他地方引起任何问题.

Answer 2

  class << self
     def instance_method_already_implemented?(method_name)
      return true if method_name =~ /^attributes/
      super
    end
  end

这个补丁很好,主要适用于我,但当你检查像Album.column_names和Album.columns.collect(&:name)这样的东西时,你仍然可以获得所有列.这也会失败.

 a = Album.last
 a = Album.new(a.attributes) 

要让rails完全忽略列,您可以执行此操作.

 class Album < ActiveRecord::Base
    set_table_name "album"
    ## --------------------- Ignore columns patch ------
    @@ignore_column_pattern = /^column_one|^column_two/

    class << self
      alias :all_columns :columns
      def columns 
        @columns_filt ||= all_columns.reject { |col| col.name =~ @@ignore_column_pattern } 
      end 
    end

    alias :all_attribute_names :attribute_names
    def attribute_names
      @attr_names_filt ||= all_attribute_names.reject { |att| att =~ @@ignore_column_pattern }
    end
    ## ------------------- / Ignore columns patch ------
    belongs_to :artist
    has_many :tracks, :through => :album_tracks
  end

我还使用了一个数组来存储我不想要的列,但你仍然可以使用正则表达式方式!现在,您可以找到有关该列的唯一方法是使用连接即.

Album.connection.columns("albums").collect(&:name)

Answer 3

（这是一个老问题，但仍然在谷歌中出现，所以我会添加一个迟来的答案）

我发现限制 ActiveRecord 模型加载的数据的最佳方法是创建一个仅包含您希望加载的列的数据库视图。您可以使用 ActiveRecord 的table_name方法将 ActiveRecord 模型指向约束视图。本机 SQL 工具仍然可以操作基础表，但 ActiveRecord 只会看到（并因此加载）显式包含在视图中的列。