has_many:通过多个has_one关系? [英] has_many :through multiple has_one relationships?

问题描述

我正在为我们在铁轨上的教堂编写指导计划(仍然是铁轨上的新手).

I'm writing a mentorship program for our church in rails (im still farily new to rails)..

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..

So basically an objects "siblings" needs to map all the children from both the father and mother not including the object itself..

这可能吗?

谢谢

丹尼尔

推荐答案

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带来一些麻烦.

It's funny how questions that appear simple can have complex answers. In this case, implementing the reflexive parent/child relationship is fairly simple, but adding the father/mother and siblings relationships creates a few twists.

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:

To start, we create tables to hold the parent-child relationships. Relationship has two foreign keys, both pointing at Contact:

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，我们将父母指向联系":

In the Relationship model we point the father and mother back to Contact:

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

并定义Contact中的逆关联:

and define the inverse associations in Contact:

class Contact < ActiveRecord::Base
  has_many :relationships, :dependent => :destroy
  has_one :father, :through => :relationships
  has_one :mother, :through => :relationships
end

现在可以创建关系了

@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:

This is not so great, what we really want is to build the relationship in a single call:

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)添加实例方法:

To find the children of a Contact, add a scope to Contact and (for convenience) an instance method:

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:

Siblings are the tricky part. We can leverage the Contact.children method and manipulate the results:

def siblings
  ((self.father ? self.father.children : []) +
   (self.mother ? self.mother.children : [])
   ).uniq - [self]
end

这不是最优的，因为father.children和mother.children将重叠(因此需要uniq)，并且可以通过制定必要的SQL来更有效地完成(留作练习:))，但请记住，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.

This is non-optimal, since father.children and mother.children will overlap (thus the need for uniq), and could be done more efficiently by working out the necessary SQL (left as an exercise :)), but keeping in mind that self.father.children and self.mother.children won't overlap in the case of half-siblings (same father, different mother), and a Contact might not have a father or a mother.

以下是完整的型号和一些规格:

Here are the complete models and some specs:

# 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

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