Friday, June 6, 2008

DataMapper: Parent / Child Relationship

I couldn't find an example at datamapper.org /docs for a parent child relationship.


After a little searching, I found the answer in the integration tests.  Here is the example:

 class Node
   include DataMapper::Resource

   def self.default_repository_name
     ADAPTER
   end

   property :id, Integer, :serial => true
   property :name, String

     has n, :children, :class_name => 'Node', :child_key => [ :parent_id ]
   belongs_to :parent, :class_name => 'Node', :child_key => [ :parent_id ]
 end

Hope that helps someone else.

Posted by Justin Pease at 8:08 PM

Labels: , , ,

6 comments:

  1. It looks more like a tree relationship then a parent/child relationship.
    ReplyDelete
  2. "In a hierarchical data model, data is organized into a tree-like structure. The structure allows repeating information using parent/child relationships: each parent can have many children but each child only has one parent."

    http://en.wikipedia.org/wiki/Hierarchical_model
    ReplyDelete
  3. This is very helpful, though I'm not too familiar with datamapper. I'm trying to see if it'll fit what I need.

    Could this be expanded to the parent becomes,
    has n, :children, :class_name => 'Node', :child_key => [:child_id]
    has n, :parents, :class_name => 'Node', :child_key => [:parent_id ]

    Something like that would work with activerecord, but, like I said I'm not too familiar.

    Cheers
    ReplyDelete
  4. scott,

    Actually I believe the syntax you suggested is what I first tried, and did not work, and caused the searching.

    DataMapper is still somewhat young, so check the integration tests referenced in the post for the most recent developments.
    ReplyDelete
  5. Ah, I figured it out.

    I didn't write a spec for it, nor would it stop any nonsensical inbred relationships, but:

    pastie.
    ReplyDelete
  6. Why not just use the dm-is-tree plugin?

    http://github.com/datamapper/dm-more/tree/master/dm-is-tree
    ReplyDelete

Subscribe to: Post Comments (Atom)