我正在为我们在铁轨上的教会编写指导计划(我仍然是铁轨上的新手)。
我需要对此建模。
contact has_one :father, :class_name => "Contact" has_one :mother, :class_name => "Contact" has_many :children, :class_name => "Contact" has_many :siblings, :through <Mother and Father>, :source => :children
因此,基本上,对象“兄弟姐妹”需要映射父亲和母亲的所有孩子,而不包括对象本身。
这可能吗?
谢谢
丹尼尔
有趣的是,看起来简单的问题如何具有复杂的答案。在这种情况下,实现自反的父母/子女关系非常简单,但是添加父亲/母亲和兄弟姐妹关系会产生一些扭曲。
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向“联系”:
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中定义逆关联:
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单个调用中建立关系:
class Contact < ActiveRecord::Base def build_father(father) relationships.build(:father=>father,:relation_type=>'father') end end
所以我们可以做:
@bart.build_father(@homer) @bart.save!
要查找联系人的子级,请将范围添加到联系人,并(为方便起见)添加一个实例方法:
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方法并处理结果:
def siblings ((self.father ? self.father.children : []) + (self.mother ? self.mother.children : []) ).uniq - [self] end
这不是最佳的,因为father.children和mother.children将不重复(因而对于需求uniq),并且可以通过制定必要的SQL(作为一个练习:))更有效地完成,但牢记self.father.children和self.mother.children在同父异母的兄弟姐妹(父亲相同,母亲不同)的情况下不会重叠,并且联系人可能没有父亲或母亲。
uniq
self.father.children
self.mother.children
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