php: dividing a multitable select into several objects / object structure - php

Question

let me at first state that we use php and postgre database. In our project we have decided not to use any ORM due to its overload of sql queries and we are taking the oposite way.
Imagine you have a select from several tables, lets say joined on id columns. For instance:
tables: users(id, name), items(id, name, description), comments(user_id, item_id, text, rating)
So basically you have a table of users, a table of some items and a table of comments which are related to one user and one item.
You create two objects - user and item representing their table row. And then you want to create a comment object. In an ORM it would contain objects user and item and they would load themselves with their queries, but that would be two queries and you re thinking...hm but I can select that data with a single query...but how?
Imagine that you have this select:
SELECT * FROM comments JOIN users ON comments.user_id = users.id JOIN items ON comments.item_id = items.id
(you can also imagine a WHERE clause with specified item id or user id etc.)
So how would you split the result of such a select into this class structure, lets say you want a list of comment objects:
user
item
comment (contains references to user and item object)
So far our theoretical solution was to prefix name of the columns with fixed prefixes :) and then propagating the result into the object structure and each objects takes what it needs from the select. Any other solutions? Lets say more sophisticated?
Thanks for any ideas
PS: obviously I have used a very simple example, but try to imagine that the problem is far larger and the structure far more complex

Answer 1

First of all, you might benefit from looking at the Data Mapper pattern. A simple use-case with would look like this:
$user = new User;
$mapper = new UserMapper( $db );
$user->setName('foobar');
$mapper->fetch( $user );
if ( $user->isBanned() )
{
throw new Exception('get out !');
}
$user->setLastActive( time() );
$mapper->store( $user );
As for the single query with data: that's not the important part. You just ALIAS it as required (oh .. and i hope you are not using the * for selecting rows). The important bit is creating an object graph from selected data. That where you use builders/factories.
//the rest of PDO-related code
$data = $statement->fecth(PDO::FETCH_ASSOC);
$comment = $commentFactory->build($data);
Where $commentFactory is instance of CommentFactory:
class CommentFactory
{
public function build( $params )
{
$author = new User;
$subject = new Item;
$comment = new Comment( $author, $subject );
$author->setId( $params['user_id']);
$author->setName( $params['user_name']);
$subject->setId( $param['item_id']);
$comment->setContent( $param['content']);
return $comment;
}
}
Additionally with setup like this, you can easily change how $comment is made, just by changing what class is the $commentFactory an instance of.