multiple query paths map to the first child model.

Question

I noticed when using multiple query paths with a model that had multiple belongs_to relationships, the other query paths would map to the first child model.

 ruby
gem 'dm-core', '~> 1.0.2'
gem 'dm-migrations', '~> 1.0.2'

require 'dm-core'
require 'dm-migrations'

class HostName

  include DataMapper::Resource
  include DataMapper::Migrations

  property :id, Serial

  property :name, String

  has 0..n, :urls

end

class Port

  include DataMapper::Resource
  include DataMapper::Migrations

  property :id, Serial

  property :number, Integer

  has 0..n, :urls

end

class Url

  include DataMapper::Resource
  include DataMapper::Migrations

  property :id, Serial

  belongs_to :host_name

  belongs_to :port

  property :path, String

end

DataMapper.setup(:default, 'sqlite3:dm_bug.db')
DataMapper.auto_migrate!

url = Url.create(
  :host_name => {:name => 'example.com'},
  :port => {:number => 80},
  :path => '/index.html'
)

# works
puts (
  Url.all('host_name.name' => 'example.com') &
  Url.all('port.number' => 80)
).first


# fails
puts Url.first(
  'host_name.name' => 'example.com',
  'port.number' => 80
)

#<0x00000001c522d0>
/home/hal/.rvm/gems/ruby-1.9.2-p136/gems/dm-do-adapter-1.0.2/lib/dm-do-adapter/adapter.rb:142:in `execute_reader': no such column: host_names.port_id (DataObjects::SyntaxError)
    from /home/hal/.rvm/gems/ruby-1.9.2-p136/gems/dm-do-adapter-1.0.2/lib/dm-do-adapter/adapter.rb:142:in `block in read'
    from /home/hal/.rvm/gems/ruby-1.9.2-p136/gems/dm-do-adapter-1.0.2/lib/dm-do-adapter/adapter.rb:260:in `with_connection'
    from /home/hal/.rvm/gems/ruby-1.9.2-p136/gems/dm-do-adapter-1.0.2/lib/dm-do-adapter/adapter.rb:138:in `read'
    from /home/hal/.rvm/gems/ruby-1.9.2-p136/gems/dm-core-1.0.2/lib/dm-core/repository.rb:162:in `read'
    from /home/hal/.rvm/gems/ruby-1.9.2-p136/gems/dm-core-1.0.2/lib/dm-core/model.rb:379:in `first'
    from dm_bug.rb:64:in `<main>'
</main>0x00000001c522d0>

Created by Postmodern - 2011-01-05 02:30:47 UTC

Original Lighthouse ticket: http://datamapper.lighthouseapp.com/projects/20609/tickets/1467

该提问来源于开源项目：datamapper/dm-core

Answer 1

Ah, as dkubb suggested using a Hash style of query seems to also work:

 ruby
puts Url.first(
  :host_name => {:name => ’example.com’},
  :port => {:number => 80}
)

by Postmodern