tagged: habtm

Rails 3.x — Self-referential has_many :through Parent<->Child relationship modelling

Stamped: 01 Sep 2010 | Show comments

Seriously?

Srsly, that's more of an SEO title than anything, because damnit, I know how the hell it works at an SQL level and it was frustrating to get working in Rails because of syntax, namely :class_name => :object, when it should be :class_name => "object". I hope someone finds this useful, because when it comes to rails 3 there's not too much stuff that's recent.

Get to the point, show me the goods

rails new confusingTitleProject
cd confusingTitleProject
rails g model Person name:string
rails g model PersonRelationship parent_id:integer child_id:integer

#App/Models/PersonRelationship.rb
class PersonRelationship < ActiveRecord::Base
  belongs_to :parent, :class_name => "Person"
  belongs_to :child, :class_name => "Person"
end

#App/Models/Person.rb
class Person < ActiveRecord::Base
  
  validates_presence_of :first_name, :last_name

  has_many     :parent_child_relationships,
               :class_name            => "PersonRelationship",
               :foreign_key           => :child_id,
               :dependent             => :destroy
  has_many     :parents,
               :through               => :parent_child_relationships,
               :source                => :parent

  has_many     :child_parent_relationships,
               :class_name            => "PersonRelationship",
               :foreign_key           => :parent_id,
               :dependent             => :destroy
  has_many     :children,
               :through               => :child_parent_relationships,
               :source                => :child
end

Then, as an example, you can do the following to add a parent:

a = Person.new; b = Person.new
b.parents = [a]

tags: rails, self join, has_many through, habtm

datamapper - many-to-many parent child relationship

Stamped: 17 Jun 2008 | Show comments

I started playing around with datamapper to see if I could model an many to many parent/child relationship (self-referential habtm?) for an upcoming project. The plan was to use sproutcore for the gui (once I figured it out!), and merb as a webservice that it interacts with.

Justin gave me a kickstart with datamapper, and I eventually came up with:

#Person.rb
class Person
  include DataMapper::Resource


  property :id, Integer, :serial => true

  has n, :relationships
  has n, :parents, :through => :relationships, :class_name => 'Person'
  has n, :children, :through => :relationships, :class_name => 'Person'


  # parent = Person.create()
  # child = Person.create()
  # relationship = Relationship.new(:parent => parent)
  # child.relationships << relationship
  # child.save

end

#Relationship.rb
class Relationship
  include DataMapper::Resource
  
  property :id, Integer, :serial => true
  belongs_to :person
  belongs_to :parent, :class_name => 'Person'
  belongs_to :child, :class_name => 'Person'
end

I'll eventually write some spec's for it.

tags: datamapper, habtm, merb