Rails ActiveRecord：没有主键的旧表显示nil结果？ [英] Rails ActiveRecord: legacy table without primary key shows nil for result?

问题描述

我有一个Rails应用程序，它将坐在旧数据库的顶部，有一些我不得不处理的丑陋的表。一个是与 features 相关的 feature_attributes 表。问题是这个 feature_attributes 表没有主键。我不会认为这将是一个问题，但显然是。我有我的模型名称不同于表名称，但我使用 set_table_name 指定正确的名称。

I've got a Rails app that'll be sitting on top of a legacy database with some ugly tables that I'm having to deal with. One is a feature_attributes table related to features. Problem is that this feature_attributes table doesn't have a primary key. I wouldn't think that'd be a problem, but evidently it is. I've got my model name which is different from the table name, but I'm using set_table_name to specify the right one.

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的与 feature_attributes 相关的功能，并调用 feature.feature_attributes nil 。事实上，即使 FeatureAttribute.first 给我 nil 。 FeatureAttribute.any？的结果会返回 false 。我担心ActiveRecord不从表中读取任何数据，因为没有主键。这是怎么回事？

Once I load a feature that I know has related feature_attributes and call feature.feature_attributes on it, I get nil. Matter of fact, even FeatureAttribute.first gives me nil. The result of FeatureAttribute.any? returns false. I'm worried that ActiveRecord isn't reading any of the data from the table because there isn't a primary key. Is that what's going on here?

feature_attribute 表有以下列。

feature_id
attribute_name
attribute_value
created_date
modified_date

帮助！

我还要注意，直接运行生成的SQL MySQL服务器实际上得到我想要的行。

I'll also note that running the generated SQL directly against the MySQL server actually gets me the rows I want.

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

EDIT ：很抱歉。下次我将学习检查我的 database.yml 。显然，我正在从一个测试数据库读取具有相同的功能表，但 feature_attribute 表是完全空的。

EDIT: I am so sorry. Next time I'll learn to check my database.yml. Evidently I was reading from a test database that had an identical feature table, but the feature_attribute table was totally empty.

我觉得自己是个白痴。谢谢大家的帮助;我会投票给你们所有的烦恼。我真的喜欢大家的答案。 （我可以自己投票吗？：））

I feel like a moron. Thanks for your help, everyone; I'm up voting you all for your troubles. I did like just about everybody's answer. (Can I down vote myself? :))

推荐答案

尝试设置主键：

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

  belongs_to :feature
end

UPDATE

我认为你的问题在别处。我只是测试和ActiveRecords工作正常与没有主键的表：

I think your problem lies anywhere else. I just tested and ActiveRecords works fine with tables without a primary key:

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：

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> 

UPDATE 2
不太好：

UPDATE 2 Not very fine:

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

这篇关于Rails ActiveRecord：没有主键的旧表显示nil结果？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！