has_many：通过多个has_one关系？
我正在为我们的铁路教堂写一个导师计划（我仍然很喜欢铁路）。
我需要对此进行建模..
contact has_one :father, :class_name => "Contact" has_one :mother, :class_name => "Contact" has_many :children, :class_name => "Contact" has_many :siblings, :through , :source => :children 所以基本上一个对象“兄弟姐妹”需要映射父亲和母亲的所有孩子，不包括对象本身。
这可能吗？
谢谢
丹尼尔
有趣的是，看似简单的问题可以得到复杂的答案。 在这种情况下，实现反身父/子关系相当简单，但添加父/母和兄弟关系会产生一些曲折。
首先，我们创建表来保存父子关系。 关系有两个外键，都指向联系人：
create_table :contacts do |t| t.string :name end create_table :relationships do |t| t.integer :contact_id t.integer :relation_id t.string :relation_type end
在关系模型中，我们将父亲和母亲指回联系人：
class Relationship < ActiveRecord::Base belongs_to :contact belongs_to :father, :foreign_key => :relation_id, :class_name => "Contact", :conditions => { :relationships => { :relation_type => 'father'}} belongs_to :mother, :foreign_key => :relation_id, :class_name => "Contact", :conditions => { :relationships => { :relation_type => 'mother'}} end
并在Contact中定义反向关联：
class Contact < ActiveRecord::Base has_many :relationships, :dependent => :destroy has_one :father, :through => :relationships has_one :mother, :through => :relationships end
现在可以创建一个关系：
@bart = Contact.create(:name=>"Bart") @homer = Contact.create(:name=>"Homer") @bart.relationships.build(:relation_type=>"father",:father=>@homer) @bart.save! @bart.father.should == @homer
这不是很好，我们真正想要的是在一次通话中建立关系：
class Contact < ActiveRecord::Base def build_father(father) relationships.build(:father=>father,:relation_type=>'father') end end
所以我们可以这样做：
@bart.build_father(@homer) @bart.save!
要查找联系人的子项，请向Contact和（为方便起见）实例方法添加范围：
scope :children, lambda { |contact| joins(:relationships).\ where(:relationships => { :relation_type => ['father','mother']}) } def children self.class.children(self) end Contact.children(@homer) # => [Contact name: "Bart")] @homer.children # => [Contact name: "Bart")]
兄弟姐妹是棘手的部分。 我们可以利用Contact.children方法并操纵结果：
def siblings ((self.father ? self.father.children : []) + (self.mother ? self.mother.children : []) ).uniq - [self] end
这是非最佳的，因为father.children和mother.children将重叠（因此需要uniq ），并且可以通过编写必要的SQL（左侧作为练习:)来更有效地完成，但请记住self.father.children和self.mother.children在半兄弟姐妹（同一个父亲，不同的母亲）的情况下不会重叠，并且联系人可能没有父亲或母亲。
以下是完整的型号和一些规格：
# app/models/contact.rb class Contact < ActiveRecord::Base has_many :relationships, :dependent => :destroy has_one :father, :through => :relationships has_one :mother, :through => :relationships scope :children, lambda { |contact| joins(:relationships).\ where(:relationships => { :relation_type => ['father','mother']}) } def build_father(father) # TODO figure out how to get ActiveRecord to create this method for us # TODO failing that, figure out how to build father without passing in relation_type relationships.build(:father=>father,:relation_type=>'father') end def build_mother(mother) relationships.build(:mother=>mother,:relation_type=>'mother') end def children self.class.children(self) end def siblings ((self.father ? self.father.children : []) + (self.mother ? self.mother.children : []) ).uniq - [self] end end # app/models/relationship.rb class Relationship < ActiveRecord::Base belongs_to :contact belongs_to :father, :foreign_key => :relation_id, :class_name => "Contact", :conditions => { :relationships => { :relation_type => 'father'}} belongs_to :mother, :foreign_key => :relation_id, :class_name => "Contact", :conditions => { :relationships => { :relation_type => 'mother'}} end # spec/models/contact.rb require 'spec_helper' describe Contact do before(:each) do @bart = Contact.create(:name=>"Bart") @homer = Contact.create(:name=>"Homer") @marge = Contact.create(:name=>"Marge") @lisa = Contact.create(:name=>"Lisa") end it "has a father" do @bart.relationships.build(:relation_type=>"father",:father=>@homer) @bart.save! @bart.father.should == @homer @bart.mother.should be_nil end it "can build_father" do @bart.build_father(@homer) @bart.save! @bart.father.should == @homer end it "has a mother" do @bart.relationships.build(:relation_type=>"mother",:father=>@marge) @bart.save! @bart.mother.should == @marge @bart.father.should be_nil end it "can build_mother" do @bart.build_mother(@marge) @bart.save! @bart.mother.should == @marge end it "has children" do @bart.build_father(@homer) @bart.build_mother(@marge) @bart.save! Contact.children(@homer).should include(@bart) Contact.children(@marge).should include(@bart) @homer.children.should include(@bart) @marge.children.should include(@bart) end it "has siblings" do @bart.build_father(@homer) @bart.build_mother(@marge) @bart.save! @lisa.build_father(@homer) @lisa.build_mother(@marge) @lisa.save! @bart.siblings.should == [@lisa] @lisa.siblings.should == [@bart] @bart.siblings.should_not include(@bart) @lisa.siblings.should_not include(@lisa) end it "doesn't choke on nil father/mother" do @bart.siblings.should be_empty end end
我完全同意zetetic。 这个问题看起来比答案简单得多，我们几乎无能为力。 我会添加我的20c。
表：
create_table :contacts do |t| t.string :name t.string :gender end create_table :relations, :id => false do |t| t.integer :parent_id t.integer :child_id end
表关系没有相应的模型。
class Contact < ActiveRecord::Base has_and_belongs_to_many :parents, :class_name => 'Contact', :join_table => 'relations', :foreign_key => 'child_id', :association_foreign_key => 'parent_id' has_and_belongs_to_many :children, :class_name => 'Contact', :join_table => 'relations', :foreign_key => 'parent_id', :association_foreign_key => 'child_id' def siblings result = self.parents.reduce [] {|children, p| children.concat p.children} result.uniq.reject {|c| c == self} end def father parents.where(:gender => 'm').first end def mother parents.where(:gender => 'f').first end end
现在我们有定期的Rails协议。 所以我们可以
alice.parents << bob alice.save bob.chidren << cindy bob.save alice.parents.create(Contact.create(:name => 'Teresa', :gender => 'f')
以及所有类似的东西。
has_and_belongs_to_many :parents, :class_name => 'Contact', :join_table => 'relations', :foreign_key => 'child_id', :association_foreign_key => 'parent_id', :delete_sql = 'DELETE FROM relations WHERE child_id = #{id}' has_and_belongs_to_many :children, :class_name => 'Contact', :join_table => 'relations', :foreign_key => 'parent_id', :association_foreign_key => 'child_id', :delete_sql = 'DELETE FROM relations WHERE parent_id = #{id}'
我使用了这个例子，但不得不添加：delete_sql来清理关系记录。 起初我在字符串周围使用双引号但发现导致错误。 切换到单引号有效。