Rails Habtm加入 [英] Rails habtm joins

问题描述

我在类别，产品和产品之间具有这种关系品牌:

class Brand < ActiveRecord::Base
  has_many :products
end

class Category < ActiveRecord::Base
  has_and_belongs_to_many :products
end

class Product < ActiveRecord::Base
  has_and_belongs_to_many :categories
  belongs_to :brand
end

如何通过这种关系按指定品牌选择所有类别? 我尝试了这个但出现错误

How can I select all categories by specified brand with this relations? I try this but get an error

b = Brand.find(1)
Category.joins(:products).where(:products => b.products)

推荐答案

您对联接做了正确的事情，只是在定义中添加了更复杂的地方:

You did the right thing with the join, just add a more complex where definition:

Category.joins(:products).where(:products => {:brand_id => 1})

这篇关于Rails Habtm加入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！