DAL (Data access layer) design question

[Popovich88]

Hi.
Lets i have two classes: Posts and Comments mapping the Posts and Comments tables from the database.

I want to get all coments from a specific post.
Should I make post->getAllComments() or comments->getByPostID(postid).
I have one class representing each table and one class represent each row of that table.

What do you think is the best way?

[Jake Arkinstall]

As the comments class is mapping comments from the database, I'd say you should use Comments->getByPostID(postid).

Of course, if the Post class has access to the Comments class, then by all means use Post->getAllComments() as a helper method which simply calls Comments->getByPostID(Post->ID).

Can't have too many helper methods :P

-edit-

It may be important to note, however, that it is useful to have the actual record class (i.e. Post, where Posts is the mapper class) unassociated from the database/mappers entirely. That way moving records to alternative database systems (e.g. a backup system) will take much less code. Post->getAllComments() implies that Post has access to the database connection, which (depending on your system design) may not be the best approach.