Rails ActiveRecord:没有主键的遗留表显示nil为结果？

Question

我有一个Rails应用程序,它将位于遗留数据库之上,其中包含一些我不得不处理的丑陋表格.一个是feature_attributes与之相关的表features.问题是该feature_attributes表没有主键.我不认为这是一个问题,但显然是.我的模型名称与表名不同,但我set_table_name用来指定正确的名称.

class Feature < ActiveRecord::Base
  has_many :feature_attributes
end

class FeatureAttribute < ActiveRecord::Base
  set_table_name 'feature_attribute'
  belongs_to :feature
end

一旦我加载了一个我知道已经相关的功能feature_attributes并调用feature.feature_attributes它,我就会得到nil.事实上,甚至FeatureAttribute.first给了我nil.FeatureAttribute.any?退货的结果false.我担心ActiveRecord没有读取表中的任何数据,因为没有主键.那是怎么回事？

该feature_attribute表包含以下列.

feature_id
attribute_name
attribute_value
created_date
modified_date

救命!

我还要注意,直接针对MySQL服务器运行生成的SQL实际上可以获得我想要的行.

SELECT `feature_attribute`.* FROM `feature_attribute` WHERE `feature_attribute`.`feature_id` = 24;

编辑:我很抱歉.下次我会学会检查我的database.yml.显然我正在从具有相同特征表的测试数据库中读取,但该feature_attribute表完全是空的.

我觉得自己像个白痴.谢谢大家的帮助; 我为你的麻烦投票给大家.我确实喜欢每个人的答案.(我可以自己投票吗？:))

Answer 1

尝试也设置主键:

class FeatureAttribute < ActiveRecord::Base
  set_table_name 'feature_attribute'
  set_primary_key 'feature_id'

  belongs_to :feature
end

UPDATE

我认为你的问题在于其他地方.我刚刚测试过,ActiveRecords可以在没有主键的情况下正常工作:

对于一个简单的表:

class CreateThings < ActiveRecord::Migration
  def change
    create_table :things, :id => false do |t|
      t.string :name

      t.timestamps
    end
  end
end

在控制台中:

Loading development environment (Rails 3.1.1)
irb(main):001:0> Thing.create(:name=>'A name for the thing')
   (0.1ms)  BEGIN
  SQL (0.3ms)  INSERT INTO `things` (`created_at`, `name`, `updated_at`) VALUES ('2011-11-02 16:33:48', 'A name for the thing', '2011-11-02 16:33:48')
   (40.3ms)  COMMIT
=> #<Thing name: "A name for the thing", created_at: "2011-11-02 16:33:48", updated_at: "2011-11-02 16:33:48">
irb(main):002:0> Thing.first
  Thing Load (0.7ms)  SELECT `things`.* FROM `things` LIMIT 1
=> #<Thing name: "A name for the thing", created_at: "2011-11-02 16:33:48", updated_at: "2011-11-02 16:33:48">
irb(main):003:0> 

更新2 不是很好:

irb(main):003:0> Thing.create(:name=>'Another thing')
   (0.2ms)  BEGIN
  SQL (0.4ms)  INSERT INTO `things` (`created_at`, `name`, `updated_at`) VALUES ('2011-11-02 16:40:59', 'Another thing', '2011-11-02 16:40:59')
   (35.4ms)  COMMIT
=> #<Thing name: "Another thing", created_at: "2011-11-02 16:40:59", updated_at: "2011-11-02 16:40:59">
irb(main):004:0> Thing.first
  Thing Load (0.5ms)  SELECT `things`.* FROM `things` LIMIT 1
=> #<Thing name: "A name for the thing", created_at: "2011-11-02 16:33:48", updated_at: "2011-11-02 16:33:48">
irb(main):005:0> Thing.last
  Thing Load (11.8ms)  SELECT `things`.* FROM `things` ORDER BY `things`.`` DESC LIMIT 1
Mysql2::Error: Unknown column 'things.' in 'order clause': SELECT  `things`.* FROM `things`  ORDER BY `things`.`` DESC LIMIT 1
ActiveRecord::StatementInvalid: Mysql2::Error: Unknown column 'things.' in 'order clause': SELECT  `things`.* FROM `things`  ORDER BY `things`.`` DESC LIMIT 1