Self Referential question in RoR compared to Java Hibernate

rubyonrails-talk
1

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?

2

Hi --

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 :slight_smile: 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

3

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?

4

Hi --

Hi,

That was a great post!

Glad to oblige :slight_smile:

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 :slight_smile: 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