Question

我有两个通过连接表连接的模型：

class Publication < ActiveRecord::Base
  attr_accessible :title, :author_attributes, :translator_attributes

  has_many :publication_contributors
  has_many :authors, :through => :publication_contributors, :source => :contributor,
    :conditions => {:publication_contributors => {:contributor_type => "Author"}}
  has_many :translators, :through => :publication_contributors, :source => :contributor,
    :conditions => {:publication_contributors => {:contributor_type => "Translator"}}

  accepts_nested_attributes_for :authors, :translators
end

class Contributor < ActiveRecord::Base
  attr_accessible :name

  has_many :publications, :through => :publication_contributors
  has_many :publication_contributors
end

class PublicationContributor < ActiveRecord::Base
  attr_accessible :contributor_type

  belongs_to :publication
  belongs_to :contributor
end

请注意，连接表具有第三个属性（在publication_id和contributor_id旁边），称为contributor_type。此属性可能包含诸如“作者”，“翻译者”，“编辑者”或其他内容的角色。在我的出版物模型中，我为两个更常见的contributor_types创建了一对关联，“Author”和“Translator”。这些关联可以很好地检索相关数据，例如@publication.authors。但是，当通过嵌套形式创建这些关联时，它会发出声音。

我的表单看起来像这样：

<%= form_for @publication, :remote => true do |f| %>

  <%= f.label :title %>:
  <%= f.text_field :title %>

  <%= f.fields_for :authors do |builder| %>
    <%= builder.label :name, "Author" %>:
    <%= builder.text_field :name %>
  <% end %>

  <%= f.fields_for :translators do |builder| %>
    <%= builder.label :name, "Translator" %>:
    <%= builder.text_field :name %>
  <% end %>

  <%= f.submit %>
<% end %>

在我的控制器中：

def create
  publication = Publication.create(params[:publication])
end

表单按预期呈现，但在创建操作期间会出现。我曾希望Rails能够根据发布关联中的条件神奇地分配适当的contributor_type，例如：

has_many :authors, :through => :publication_contributors, :source => :contributor,
:conditions => {:publication_contributors => {:contributor_type => "Author"}}

不幸的是，事实并非如此。我在创建过程中遇到此错误：

Mysql2::Error: Column 'contributor_type' cannot be null

这让我觉得我唯一的办法是在before_create回调中手动分配contributor_type，但如果是这种情况，我该如何确定要分配的类型？参数在其名称中具有正确的类型，例如：

publication[authors_attributes][0][name]

有没有办法在模型层中访问该信息？

更新：

我的new行动：

def new
  @publication = Publication.new
  publication_contributor = @publication.publication_contributors.build
  contributor = publication_contributor.contributor.build
end

它会在最后一行（一个设置contributor）上抛出此错误：

undefined method `build' for nil:NilClass

Answer 1

您可以尝试以下方法吗？

class Publication < ActiveRecord::Base
  attr_accessible :title, :publication_contributors_attributes

  has_many :publication_contributors
  has_many :authors, through: :publication_contributors, source: :contributor, conditions: { publication_contributors: { contributor_type: 'Author' } }
  has_many :translators, through: :publication_contributors, source: :contributor, conditions: { publication_contributors: { contributor_type: 'Translator' } }

  accepts_nested_attributes_for :publication_contributors
end

class Contributor < ActiveRecord::Base
  attr_accessible :name

  has_many :publications, through: :publication_contributors
  has_many :publication_contributors
end

class PublicationContributor < ActiveRecord::Base
  attr_accessible :contributor_type

  belongs_to :publication
  belongs_to :contributor

  accepts_nested_attributes_for :contributor
end

<%= form_for @publication, :remote => true do |f| %>

  <%= f.label :title %>:
  <%= f.text_field :title %>

  <%= f.fields_for :publication_contributors do |pc_form| %>
    <%= pc_form.hidden_field :contributor_type %>
    <%= pc_form.fields_for :contributor do |c_form| %>
      <%= c_form.label :name, "Author" %>:
      <%= c_form.text_field :name %>
    <% end %>
  <% end %>

  <%= f.submit %>
<% end %>

更新：控制器代码

@publication.publication_contributors.build
@publication.publication_contributors.each do |pc|
  pc.build_contributor
end

Rails：在嵌套表单中操作连接表

1 个答案: