Will Doctrine2 select all fields on all associations (JOINS from a query) to populate the full aggregate object? - doctrine-orm

Question

I'm researching whether to try Doctrine2 or not. One thing that scares me is the over SELECTing of columns I don't need (ie. consider lots of varchars being selected unnecessarily).
You might ask: but don't you want your full entity object filled? Yes, unless I'm looking for an array hydration. However, many times I don't need the full aggregation filled. Take the association shown below. If I query the Users table with a JOIN on Address, will all the columns from the address table be SELECTed as well (and therefore populated into an address object inside of users object)? Now imagine we have more JOINs. This could get really bad. What if I only want the fields from User populated in just a users only object? I guess I'm a little confused at what Doctrine is doing behind the scenes with associations and query JOINs.
/** #Entity **/
class User
{
// ...
/**
* #ManyToOne(targetEntity="Address")
* #JoinColumn(name="address_id", referencedColumnName="id")
**/
private $address;
}
/** #Entity **/
class Address
{
// ...
}
So does Doctrine2 populate all the fields of all the objects within the aggregate after a query (unless I specifiy partial)?

Answer 1

It depends on your query, but generally it is not implicit.
Using the query builder, you can fetch the associated record like this:
<?php
$qb = $em->createQueryBuilder();
$query = $qb->select(array("u", "a"))
->from("User", "u")
->innerJoin("u.address", "a")
->getQuery();
In the select() statement you specify what to fetch, in this case you get both.
If you only fetch the User records, then when you get the associated record with $user->getAddress(), Doctrine will make the query on the fly and hydrate the Address record for you.
That said, performance wise it is better to select both entities so Doctrine will make only one query and not 1+N queries