sql - 如何改变 Rails belongs_to 的行为

Question

我有两个模型:

class Sentence < ActiveRecord::Base
  attr_accessible :sentence_id, :authority_name #...
end

class Rule < ActiveRecord::Base
  attr_accessible :description, :headline, :note, :sentence_id
end

我想知道如何在 Rule 上创建 belongs_to :sentence 关联，其行为类似于此伪 SQL 代码:

SELECT * FROM rules 
INNER JOIN sentences ON rules.sentence_id = sentences.sentence_id;

编辑:

我想要这样的东西

rule = Rule.find 797 
# we all know how SQL query will look like...
rule.sentence  
# => SELECT * FROM sentences 
     INNER JOIN rules ON rules.sentence_id = sentences.sentence_id 
     WHERE rules.id = 797

Answer 1

首先，sentence_id 是sentences 表的主键吗？

如果是这样，那么您只需要将该列显式设置为主键即可。

class Sentence < ActiveRecord::Base
  set_primary_key :sentence_id
end

class Rule < ActiveRecord::Base
  belongs_to :sentence
end

如果sentence_id不是主键，那么需要指定它作为关联的“主键”。我没有机会测试代码，但它应该是这样的:

class Rule < ActiveRecord::Base
  belongs_to :sentence, :primary_key => :sentence_id
end