datamapper_deep_nesting.rb

#!/usr/bin/env ruby
#
# A one file test to show ...
require 'rubygems'
require 'dm-core'


# setup the logger
DataMapper::Logger.new(STDOUT, :debug)

# connect to the DB
DataMapper.setup(:default, 'sqlite3::memory:')

class User
  include DataMapper::Resource

  # properties
  property :id, Serial

  has n, :children
  has n, :grandchildren, :through => :children

end

class Child
  include DataMapper::Resource

  # properties
  property :id, Serial

  belongs_to :user
  has n, :grandchildren

end

class Grandchild
  include DataMapper::Resource

  # properties
  property :id, Serial

  belongs_to :child
  belongs_to :user, :through => :child
  has n, :greatgrandchildren

end

class Greatgrandchild
  include DataMapper::Resource

  # properties
  property :id, Serial

  belongs_to :grandchild
  belongs_to :user, :through => :grandchild

end

DataMapper.auto_migrate!

# put the code here!

@user1 = User.create
@child = @user1.children.create
@grandchild = @child.grandchildren.create
@greatgrandchild = @grandchild.greatgrandchildren.create

@user2 = User.create
@child = @user2.children.create
@grandchild = @child.grandchildren.create
@greatgrandchild = @grandchild.greatgrandchildren.create

@user = User.first
p Greatgrandchild.all(:user => @user)

__END__

#SQL output includes this:
SELECT "id", "grandchild_id" FROM "greatgrandchildren" WHERE "id" = 1 ORDER BY "id"