Rails - Apr 2007 - How-to: Hierarchical model object: Object with relation to it's own class

Hi all please advice me on the ''proper'' way to handle the
questions
below. Any insight, best-practise or hint is very welcome. I use Ruby
for a while, but Rails is new to me.

==Initial code:
===My DB contains:
CREATE TABLE `posts` (
  `id` int(10) unsigned NOT NULL auto_increment,
  `name` varchar(50) NOT NULL,
  `parent` int(10) unsigned default NULL,
  `description` varchar(255) NOT NULL,
  PRIMARY KEY  (`id`),
  UNIQUE KEY `name` (`name`)
);
INSERT INTO `posts` VALUES (1, ''mainroot'', NULL, ''a
root-post without
a parent, but with childs'');
INSERT INTO `posts` VALUES (2, ''left trunk'', 1, ''this
root has a
parent and child'');
INSERT INTO `posts` VALUES (3, ''left leaf'', 2, ''a
leaf-post with
parent, but without child'');
INSERT INTO `posts` VALUES (4, ''right leaf'', 1, ''this
leaf-post has a
parent, but no child'');

===My model file post.rb contains:
class Post < ActiveRecord::Base
  def Post::find_roots
    all_posts = Post::find_all
    all_posts.find_all {|post| not post.has_parent?}
  end
  def has_parent?
    not @parent == nil
  end
end

The DB has only an id of the parent post, so I try to map this to a
post-object like this:
class Post < ActiveRecord::Base
  attr_reader :parent
  def initialize(*args)
    puts "TEST"
    super(*args)
    unless self.parent_id == nil
      @parent = Post::get_id(self.parent_id)
    else
      @parent = nil
    end
  end
end

??When I run http://localhost:3001/Post/list I get a list of posts, so
so far so good but "TEST" is not printed, so it seems like
Post#initialize is never called. Is this true? And how to solve this?

===Controller-file:
class PostController < ApplicationController
  scaffold :post
  def list
    @posts = Post::find_roots
    puts @posts.length
  end
end

By the way, the controller-file (above) doesn''t print the number of
root-posts, but prints the total number of posts. This is makes sence,
since Post#initialize above was never run...


Reading a bit more on internet about relations I find that the Rails''
way of handling relations is more like:
==New code:
===DB:
ALTER TABLE `posts` CHANGE `parent` `post_id` INT( 10 ) UNSIGNED NULL
DEFAULT NULL
This is a bit more cryptic, but Rails expects this name in the next
step.
??Is there any way to use a different fieldname here? ''Parent''
is a
lot more explaining then ''post_id''...

===New model-file:
class Post < ActiveRecord::Base
  belongs_to :post
  has_many :post
  def Post::find_roots
    all_posts = Post::find_all
    all_posts.find_all {|post| not post.has_parent?}
  end
  def has_parent?
    not self.post == nil
  end
end

??For some reason this makes the controller (described above) return
zero. Is my Post#has_parent? correct? A test shows that it is called
for all elements, but the test contained is somehow wrong.

Basically: am I on the right by implementing the relation between Post
and parent-Post like this?

All insight and tips are welcome!

Cheers,
Paul


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I found the acts_as_tree keyword on
http://www.railsforum.com/viewtopic.php?id=1560
that will probably make life a lot easier in the above scenario.

Any comment is still welcome ofcourse. :)
Cheers,
Paul

On 8 apr, 20:37, "pjvleeu...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org"
<pjvleeu...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
> Hi all please advice me on the ''proper'' way to handle the
questions
> below. Any insight, best-practise or hint is very welcome. I use Ruby
> for a while, but Rails is new to me.
>
> ==Initial code:
> ===My DB contains:
> CREATE TABLE `posts` (
>   `id` int(10) unsigned NOT NULL auto_increment,
>   `name` varchar(50) NOT NULL,
>   `parent` int(10) unsigned default NULL,
>   `description` varchar(255) NOT NULL,
>   PRIMARY KEY  (`id`),
>   UNIQUE KEY `name` (`name`)
> );
> INSERT INTO `posts` VALUES (1, ''mainroot'', NULL,
''a root-post without
> a parent, but with childs'');
> INSERT INTO `posts` VALUES (2, ''left trunk'', 1,
''this root has a
> parent and child'');
> INSERT INTO `posts` VALUES (3, ''left leaf'', 2,
''a leaf-post with
> parent, but without child'');
> INSERT INTO `posts` VALUES (4, ''right leaf'', 1,
''this leaf-post has a
> parent, but no child'');
>
> ===My model file post.rb contains:
> class Post < ActiveRecord::Base
>   def Post::find_roots
>     all_posts = Post::find_all
>     all_posts.find_all {|post| not post.has_parent?}
>   end
>   def has_parent?
>     not @parent == nil
>   end
> end
>
> The DB has only an id of the parent post, so I try to map this to a
> post-object like this:
> class Post < ActiveRecord::Base
>   attr_reader :parent
>   def initialize(*args)
>     puts "TEST"
>     super(*args)
>     unless self.parent_id == nil
>       @parent = Post::get_id(self.parent_id)
>     else
>       @parent = nil
>     end
>   end
> end
>
> ??When I runhttp://localhost:3001/Post/listI get a list of posts, so
> so far so good but "TEST" is not printed, so it seems like
> Post#initialize is never called. Is this true? And how to solve this?
>
> ===Controller-file:
> class PostController < ApplicationController
>   scaffold :post
>   def list
>     @posts = Post::find_roots
>     puts @posts.length
>   end
> end
>
> By the way, the controller-file (above) doesn''t print the number
of
> root-posts, but prints the total number of posts. This is makes sence,
> since Post#initialize above was never run...
>
> Reading a bit more on internet about relations I find that the
Rails''
> way of handling relations is more like:
> ==New code:
> ===DB:
> ALTER TABLE `posts` CHANGE `parent` `post_id` INT( 10 ) UNSIGNED NULL
> DEFAULT NULL
> This is a bit more cryptic, but Rails expects this name in the next
> step.
> ??Is there any way to use a different fieldname here?
''Parent'' is a
> lot more explaining then ''post_id''...
>
> ===New model-file:
> class Post < ActiveRecord::Base
>   belongs_to :post
>   has_many :post
>   def Post::find_roots
>     all_posts = Post::find_all
>     all_posts.find_all {|post| not post.has_parent?}
>   end
>   def has_parent?
>     not self.post == nil
>   end
> end
>
> ??For some reason this makes the controller (described above) return
> zero. Is my Post#has_parent? correct? A test shows that it is called
> for all elements, but the test contained is somehow wrong.
>
> Basically: am I on the right by implementing the relation between Post
> and parent-Post like this?
>
> All insight and tips are welcome!
>
> Cheers,
> Paul

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