如何使用多对多关系

Question

我在业务和类别之间有多对多的关系

class Business < ActiveRecord::Base
  attr_accessible :name
  has_and_belongs_to_many :categories
end

class Category < ActiveRecord::Base
  attr_accessible :name
  has_and_belongs_to_many :businesses
end

如何创建具有2个关联类别的业务？

cat1 = Category.create(name: 'cat1')
cat2 = Category.create(name: 'cat2')
biz = Business.create(name: 'biz1'....

Answer 1

一种选择是使用accepts_nested_attributes_for，如下所示：

class Business < ActiveRecord::Base
  attr_accessible :name
  has_and_belongs_to_many :categories
  accepts_nested_attributes_for :businesses_categories
end

class Category < ActiveRecord::Base
  attr_accessible :name
  has_and_belongs_to_many :businesses
end

class BusinessesCategories < ActiveRecord::Base
    accepts_nested_attributes_for :categories
end

然后你就可以像这样创建你的表单：

<%= form_for @business do |f| %>
    <%= f.fields_for :businesses_categories do |b| %>
         <%= b.fields_for :categories do |c| %>
             <%= c.text_field :cat %>
         <% end %>
    <% end %>
<% end %>

为此，您必须在控制器中构建category对象：

#app/controllers/businesses_controller.rb
def new
    @business = Business.new
    2.times do { @business.categories.build }
end

或者，您必须从一个单独的函数调用，将类别数据输入到他们自己的表中，并将business_id设置为您想要的值

Answer 2

这是指定多对多关系的另一种方式

类Business < ActiveRecord::Base

-- has_many :business_categories

* has_many :类别，通过：:business_categories

结束

类类别< ActiveRecord::Base

-- has_many :business_categories

* has_many :企业，通过：:business_categories

结束

类Business_category < ActiveRecord::Base

** belongs_to :类别

** belongs_to :企业

结束

请参阅以下链接：：http://guides.rubyonrails.org/association_basics.html