在 has_many_through 连接模型上设置属性

Question

我在Contributor 和Resource 之间通过Contributorship 建立了has_many_through 关系。不同寻常的是，当我建立关联时，我需要为 :

设置contribution_type

model Contributor

  has_many contributorships
  has_many contributors, through: contributorships

end

model Resource

  has_many contributorships
  has_many resources, through: contributorships

end

model Contributorships

  attr_accessible :contribution_type, :contributor, :archive_resource

  belongs_to resources
  belongs_to contributors

end

建立关联涉及：

c = Contributor.create!()
r = Resource.create!()
c.contributorships.create!(resource:r,  contribution_type: :author)

或者（如果我不想提前保存）：

c = Contributor.new()
r = Resource.new()
cs = Contributorship.new(contributor:c, resource:r,  contribution_type: :author)
c.save!
r.save!
cs.save!

如果我不需要在 Contributorship 加入模型上设置 contribution_type 属性，我可以这样做：

c.resources << r

那么有没有更优雅的方式来做到这一点和同时设置属性？

Answer 1

您可以使用build 自动设置实例化对象之间的关联。

contributor = Contributor.new
contributor.contributorships.build(:contribution_type => :author)
contributor.resources.build
contributor.save!

Answer 2

如果contributor_type 的值依赖于来自其他模型之一的值，我倾向于只编写一个 before_validation 回调来在每次创建 Contributorships 时设置正确的对应值。即

model Contributorships

  attr_accessible :contribution_type, :contributor, :archive_resource

  belongs_to resources
  belongs_to contributors

  before_validation :set_contributor_type

  def set_contributor_type
     if self.new_record?
        # Whatever code you need to determine the type value
        self.contributor_type = value
     end
  end

end

如果这是用户定义的值，那么您需要使用 accepts_nested_attributes_forin 模型定义您的 contributor_type，然后在表单中使用 fields_for 以允许用户在创建时设置值记录。以下 railscast 非常全面和详细地介绍了这一点：http://railscasts.com/episodes/197-nested-model-form-part-2?view=asciicast

即：

<%= form_for(contributor) do |f| %>
   # Whatever fields you want to save for the contributor
   <% contributorship = f.object.contributorships.build %>
   <%= f.fields_for(:contributorships, contributorship) do |new_contributorship| %>
         # Whatever fields you want to save for the contributorship
         <% resource = new_contributorship.object.resources.build %>
         <%= f.fields_for(:resources, resource) do |new_resource| %>
                # Whatever fields you want to save for the resource
         <% end %>
   <% end %>
<% end %>