ActiveRecord："WHERE IN“SQL语句

Question

我有以下SQL语句：SELECT article_id FROM publications WHERE category_id IN (SELECT id FROM categories WHERE parent_id = 3)

如何将其转换为Rails ActiveRecord？

我已经尝试过了：Article.find(:all, :conditions => ["publications.category_id IN(?)", 3], :include => [:publications])，它返回空数组。

型号：

class Article < ActiveRecord::Base
  has_many :publications
  has_many :categories, :through => :publications

class Category < ActiveRecord::Base
  belongs_to :parent, :class_name => 'Category'
  has_many :children, :class_name => 'Category', :foreign_key => :parent_id
  has_many :articles, :through => :publications
  has_many :publications


class Publication < ActiveRecord::Base
  belongs_to :article
  belongs_to :category

Answer 1

这样行得通吗？

Article.find(:all, 
             :conditions => ["publications.category_id IN(SELECT id FROM categories WHERE parent_id = ?)", 3], 
             :include => [:publications])

我建议你用ancestry来表示数据库中的树形结构，还有a railcast about ancestry

Answer 2

你的模型是什么样子的？

您需要在文章、类别和发布模型中正确设置关联。

听起来您已经在表中设置了相关的外键，但是您的模型不知道如何查找关联