Rails - Mar 2007 - Self Referential question in RoR compared to Java Hibernate

I have a MySQL table.  Its light schema as follows

Comments
id int not null, auto-inc. unsigned
comment text, not null
comment_id, int,                               ##This is the parent_id
of the comment if it exist.
some other irrelevant fields

In the RoR Comment model I have
def Comment < ActiveRecord::Base
  has_and_belongs_to_many :comments
end



Java hibernate comparison (high level)

What I have to do in hibernate is change the hbm XML class for
Comments to let hibernate know that Comments could have many children
with a default attrib as Lazy (More on Lazy to come).   Then I would
have to edit the Comment Class to include the Set (childrenSet) that I
just set up in the Comments hbm XML file.  Now when I get a comment,
any comment I could check the set to see if I had any children.  The
important part here is that as long as I had my DB session open, I
would have to "Request" the childrenSet by asking for the childrenSet
(ie getChildrenSet).  If I never asked for the childrenSet hibernate
would never get nor instantiate those objects (this is the definition
of "lazy" mentioned above)

So what I would like to know is two things.

How would I get all children for a particular comment in RoR in the
view?
Is there such a feature as lazy in RoR?

BTW, do you think the field named comment in my comments table could
get a little tricky with all the RoR rules?


--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---

Hi --

On 3/6/07, dougd1101 <dougd1101-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
> I have a MySQL table.  Its light schema as follows
>
> Comments
> id int not null, auto-inc. unsigned
> comment text, not null
> comment_id, int,                               ##This is the parent_id
> of the comment if it exist.
> some other irrelevant fields
>
> In the RoR Comment model I have
> def Comment < ActiveRecord::Base
>   has_and_belongs_to_many :comments
> end
>
>
>
> Java hibernate comparison (high level)
>
> What I have to do in hibernate is change the hbm XML class for
> Comments to let hibernate know that Comments could have many children
> with a default attrib as Lazy (More on Lazy to come).   Then I would
> have to edit the Comment Class to include the Set (childrenSet) that I
> just set up in the Comments hbm XML file.  Now when I get a comment,
> any comment I could check the set to see if I had any children.  The
> important part here is that as long as I had my DB session open, I
> would have to "Request" the childrenSet by asking for the
childrenSet
> (ie getChildrenSet).  If I never asked for the childrenSet hibernate
> would never get nor instantiate those objects (this is the definition
> of "lazy" mentioned above)
>
> So what I would like to know is two things.
>
> How would I get all children for a particular comment in RoR in the
> view?
@comment.children  # or equivalent
> Is there such a feature as lazy in RoR?
The collection won''t get loaded unless you ask for it -- and even
then, under some circumstances it will be loaded lazily. You can also
do "eager" loading; see the :include parameter for
ActiveRecord::Base.find.
> BTW, do you think the field named comment in my comments table could
> get a little tricky with all the RoR rules?
Yes :-)  In fact, your modeling needs to be fixed a bit.  I''d
recommend something like:

  Table columns:
  id
  body
  parent_id
  etc.

  Model file:
  class Comment < ActiveRecord::Base
    has_many :children, :class_name => "Comment", :foreign_key
=> "parent_id"
    belongs_to :parent, :class_name => "Comment",
"foreign_key" => "parent_id"
    # etc. -- other code as needed
  end

That way you''re not being ambiguous when you say: @comment.comment,
which in your model could be either the body or the parent. Also, I
don''t think you need habtm, since presumably a comment only has one
parent.


David

-- 
Q. What is THE Ruby book for Rails developers?
A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black)
   (See what readers are saying!  http://www.rubypal.com/r4rrevs.pdf)
Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
A. Ruby Power and Light, LLC (http://www.rubypal.com)

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---

Hi,

That was a great post!

You are absolutly correct a comment will only have at most one
parent.  Should have thought about it a little more.

However in an earlier question I posted
http://groups.google.com/group/rubyonrails-talk/browse_thread/thread/a1cf4d850d90ccb1?hl=en
someone suggested I call the parent_id, comment_id.  Isn''t this the
Ruby way?

On Mar 6, 5:26 pm, "David A. Black"
<dbl...-TKXtfPMJ4Ozk1uMJSBkQmQ@public.gmane.org>
wrote:
> Hi --
>
> On 3/6/07, dougd1101
<dougd1...-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>
>
>
>
>
> > I have a MySQL table.  Its light schema as follows
>
> > Comments
> > id int not null, auto-inc. unsigned
> > comment text, not null
> > comment_id, int,                               ##This is the parent_id
> > of the comment if it exist.
> > some other irrelevant fields
>
> > In the RoR Comment model I have
> > def Comment < ActiveRecord::Base
> >   has_and_belongs_to_many :comments
> > end
>
> > Java hibernate comparison (high level)
>
> > What I have to do in hibernate is change the hbm XML class for
> > Comments to let hibernate know that Comments could have many children
> > with a default attrib as Lazy (More on Lazy to come).   Then I would
> > have to edit the Comment Class to include the Set (childrenSet) that I
> > just set up in the Comments hbm XML file.  Now when I get a comment,
> > any comment I could check the set to see if I had any children.  The
> > important part here is that as long as I had my DB session open, I
> > would have to "Request" the childrenSet by asking for the
childrenSet
> > (ie getChildrenSet).  If I never asked for the childrenSet hibernate
> > would never get nor instantiate those objects (this is the definition
> > of "lazy" mentioned above)
>
> > So what I would like to know is two things.
>
> > How would I get all children for a particular comment in RoR in the
> > view?
>
> @comment.children  # or equivalent
>
> > Is there such a feature as lazy in RoR?
>
> The collection won''t get loaded unless you ask for it -- and even
> then, under some circumstances it will be loaded lazily. You can also
> do "eager" loading; see the :include parameter for
> ActiveRecord::Base.find.
>
> > BTW, do you think the field named comment in my comments table could
> > get a little tricky with all the RoR rules?
>
> Yes :-)  In fact, your modeling needs to be fixed a bit.  I''d
> recommend something like:
>
>   Table columns:
>   id
>   body
>   parent_id
>   etc.
>
>   Model file:
>   class Comment < ActiveRecord::Base
>     has_many :children, :class_name => "Comment", :foreign_key
=> "parent_id"
>     belongs_to :parent, :class_name => "Comment",
"foreign_key" => "parent_id"
>     # etc. -- other code as needed
>   end
>
> That way you''re not being ambiguous when you say:
@comment.comment,
> which in your model could be either the body or the parent. Also, I
> don''t think you need habtm, since presumably a comment only has
one
> parent.
>
> David
>
> --
> Q. What is THE Ruby book for Rails developers?
> A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black)
>    (See what readers are saying!  http://www.rubypal.com/r4rrevs.pdf)
> Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
> A. Ruby Power and Light, LLC (http://www.rubypal.com)

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---

Hi --

On 3/6/07, dougd1101 <dougd1101-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
wrote:
>
> Hi,
>
> That was a great post!
Glad to oblige :-)
> You are absolutly correct a comment will only have at most one
> parent.  Should have thought about it a little more.
>
> However in an earlier question I posted
>
http://groups.google.com/group/rubyonrails-talk/browse_thread/thread/a1cf4d850d90ccb1?hl=en
> someone suggested I call the parent_id, comment_id.  Isn''t this
the
> Ruby way?
There''s no specific Ruby way to name columns in a relational database
:-)  As for ActiveRecord: Luke was telling you about the default
(comment_id for a Comment association), but as he said, you can use
:foreign_key to override it.  I think parent is a much better thing to
call a comment''s, ummm, parent than comment is. So I''d do the
override.


David

-- 
Q. What is THE Ruby book for Rails developers?
A. RUBY FOR RAILS by David A. Black (http://www.manning.com/black)
   (See what readers are saying!  http://www.rubypal.com/r4rrevs.pdf)
Q. Where can I get Ruby/Rails on-site training, consulting, coaching?
A. Ruby Power and Light, LLC (http://www.rubypal.com)

--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en
-~----------~----~----~----~------~----~------~--~---