Doctrine_manual-1-2-en

Chapter 8: Working with Models 109
// test.php
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8-36
// ...
$user = Doctrine_Core::getTable('User')->find(5);
$user->GroupUser->remove(0)->remove(1);
$user->save();
This is due to a fact that the call to $user->GroupUser loads all Group links for given User.
This can be time-consuming task if the User belongs to many Groups. Even if the user
belongs to few groups this will still execute an unnecessary SELECT statement.
Fetching Objects
Normally when you fetch data from database the following phases are executed:
1. Sending the query to database
2. Retrieve the returned data from the database
In terms of object fetching we call these two phases the 'fetching' phase. Doctrine also has
another phase called hydration phase. The hydration phase takes place whenever you are
fetching structured arrays / objects. Unless explicitly specified everything in Doctrine gets
hydrated.
Lets consider we have Users and Phonenumbers with their relation being one-to-many. Now
consider the following plain sql query:
// test.php
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// ...
$sql = 'SELECT u.id, u.username, p.phonenumber FROM user u LEFT JOIN
phonenumber p ON u.id = p.user_id';
$results = $conn->getDbh()->fetchAll($sql);
If you are familiar with these kind of one-to-many joins it may be familiar to you how the basic
result set is constructed. Whenever the user has more than one phonenumbers there will be
duplicated data in the result set. The result set might look something like:
index u.id u.username p.phonenumber
0 1 Jack Daniels 123 123
1 1 Jack Daniels 456 456
2 2 John Beer 111 111
3 3 John Smith 222 222
4 3 John Smith 333 333
5 3 John Smith 444 444
Here Jack Daniels has two Phonenumbers, John Beer has one whereas John Smith has three.
You may notice how clumsy this result set is. Its hard to iterate over it as you would need
some duplicate data checking logic here and there.
Doctrine hydration removes all duplicated data. It also performs many other things such as:
1. Custom indexing of result set elements
2. Value casting and preparation
3. Value assignment listening
4. Makes multi-dimensional array out of the two-dimensional result set array, the
number of dimensions is equal to the number of nested joins
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