#1065 Self-Referential has many doesn't works. - DataMapper

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#1065 ✓resolved

Self-Referential has many doesn't works.

Reported by Mauricio Eduardo Szabo | September 30th, 2009 @ 10:21 AM | in 0.10.2

Well, I just followed the site's tutorial on Self-Referential Has, and belongs to, many, but when I try to auto-migrate the column, it gives me an error. The code I'm trying to use is:

require 'dm-core'

class User
  include DataMapper::Resource

  property :id, Serial
  property :name, String, :nullable => false

  has n, :friended_users
  has n, :friends, :through => :friended_users, :class_name => "User",
                   :child_key => [:user_id]
  has n, :friended_by, :through => :friended_users, :class_name => "User",
                       :remote_name => :user, :child_key => [:friend_id]
end

class FriendedUser
  include DataMapper::Resource

  property :user_id, Integer, :key => true
  property :friend_id, Integer, :key => true

  belongs_to :user, :child_key => [:user_id]
  belongs_to :friend, :class_name => "User", :child_key => [:friend_id]
end

DataMapper.setup :default, 'sqlite3::memory:'
DataMapper.auto_migrate!

and the error:

    from /usr/lib/ruby/gems/1.8/gems/dm-core-0.10.0/lib/dm-core/property_set.rb:169:in `map'
    from /usr/lib/ruby/gems/1.8/gems/dm-core-0.10.0/lib/dm-core/property_set.rb:169:in `initialize'                          
    from /usr/lib/ruby/gems/1.8/gems/dm-core-0.10.0/lib/dm-core/associations/many_to_many.rb:23:in `new'                     
    from /usr/lib/ruby/gems/1.8/gems/dm-core-0.10.0/lib/dm-core/associations/many_to_many.rb:23:in `child_key'               
    from /usr/lib/ruby/gems/1.8/gems/dm-core-0.10.0/lib/dm-core/model.rb:695:in `assert_valid'                               
    from /usr/lib/ruby/gems/1.8/gems/dm-core-0.10.0/lib/dm-core/model.rb:694:in `each_value'                                 
    from /usr/lib/ruby/gems/1.8/gems/dm-core-0.10.0/lib/dm-core/model.rb:694:in `assert_valid'                               
    from /usr/lib/ruby/gems/1.8/gems/dm-core-0.10.0/lib/dm-core/model.rb:693:in `each_value'                                 
     ... 6 levels...
    from /usr/lib/ruby/gems/1.8/gems/dm-core-0.10.0/lib/dm-core/migrations.rb:48:in `repository_execute'
    from /usr/lib/ruby/gems/1.8/gems/dm-core-0.10.0/lib/dm-core/migrations.rb:36:in `auto_migrate_down!'
    from /usr/lib/ruby/gems/1.8/gems/dm-core-0.10.0/lib/dm-core/migrations.rb:21:in `auto_migrate!'
    from /tmp/test.rb:27

Comments and changes to this ticket

You flagged this item as spam.
haarmann (at recordjob) October 1st, 2009 @ 05:38 AM
same here, the error is

dm-core-0.10.1/lib/dm-core/property_set.rb:169:in initialize': undefined methodname' for nil:NilClass (NoMethodError)

any help appreciated.
Dan Kubb (dkubb) October 7th, 2009 @ 01:18 PM
- Milestone set to “0.10.2”
- State changed from “new” to “accepted”
- Assigned user set to “Dan Kubb (dkubb)”
You flagged this item as spam.
Mislav November 1st, 2009 @ 08:42 AM
I tried a simpler approach in 0.10.1, but the JOIN doesn't alias the second occurrence of "users" table so it can't possibly work. I guess subselects in 0.10.2 will solve this
Dan Kubb (dkubb) November 10th, 2009 @ 03:41 AM
@Mislav: Yes, I would expect the change to subselects will resolve this problem, while also opening up more complex queries than could reasonably be formed using the INNER JOIN syntax. I have been using subselects in some cases, but have not switched M:M associations over to using them. I expect to be able to get this done soon tho.
You flagged this item as spam.
Mislav December 17th, 2009 @ 05:38 PM
- Tag set to “many-to-many, self-referential”
0.10.2 is out, I hoped that this will get in.

I have an app with self-referential many-many (following/followers) and I have to go through ugly hacks to be able to make queries at all.

I'll try to help make some failing tests when I have time.
Dan Kubb (dkubb) December 30th, 2009 @ 03:49 PM
Attached is a script that works with forthcoming changes (today).

Note that you can't specify :child_key or :parent_key on a m:m relationship. They have to be specified on the relationship that is actually linking to the join table.
- ticket-1065.rb 865 Bytes
You flagged this item as spam.
Mislav December 30th, 2009 @ 04:06 PM
That was fast! Thanks!
Dan Kubb (dkubb) December 30th, 2009 @ 04:10 PM
- State changed from “accepted” to “resolved”
(from [4cb77c36e1f16a70facd853ad5c7298d24746eaa]) Fix bug with self referential many to many relationships
- Alias tables in m:m queries when necessary
- Move the query conditions from the relationships from the WHERE clause to the ON clause.
- NOTE: need to clean up SQL generation soon. This was a really painful fix, and the code needs major refactoring in order to resolve other outstanding tickets.
[#902 state:resolved] [#1065 state:resolved] http://github.com/datamapper/dm-core/commit/4cb77c36e1f16a70facd853...

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