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Related objects in xPDO can be accessed via newQuery, as shown earlier, or through xPDOObject's helper functions, getOne and getMany (depending on the relationship.

Retrieving Objects

First off, let's look at the related object retrieval methods:


Let's say we have a Car object, that has an Owner related object. Each Car can have only one Owner, which is a table with ID, name, and email. We want to grab the Owner, given that we have the Car object:

$car = $xpdo->getObject('Car',123);

$owner = $car->getOne('Owner');
echo 'The owner of this car is: '.$owner->get('name');

getOne also takes a $criteria and $cacheFlag parameter, similar to getObject and getCollection. This allows you to do a bit more filtering should you so desire.


Now say we have Wheel objects for our Car - obviously there can be more than one Wheel per Car, and we want to grab the whole collection of them. The Wheel object has 'id' and 'position' fields:

$car = $xpdo->getObject('Car',123);

$wheels = $car->getMany('Wheel');
foreach ($wheels as $wheel) {
   echo 'Got the '.$wheel->get('position').' wheel!<br />';

/* This would echo:
Got the Front Left wheel!
Got the Front Right wheel!
Got the Back Left wheel!
Got the Back Right wheel! */

As you can see, this allows us to quickly and easily grab related objects with ease.

xPDO also has methods for adding related objects to an existing Object, to make saving easier:


So we have our Car object, but say we want to set it a new owner that we've just created. We can use addOne to easily add it in:

$car = $xpdo->getObject('Car',123);
$owner = $xpdo->getObject('Owner',array('name' => 'Mark'));

Saving the Car object will save the 'owner' field on the Car row to the Owner's ID, via the relationship definition.

You can also do this with new (unsaved) objects; the save function will cascade and save both objects. Let's say we have a Car object, but we're adding an entirely new Owner:

$car = $xpdo->getObject('Car',324);

$owner = $xpdo->newObject('Owner');


This will save both the Car and the Owner object, and relate them together.

Both addOne and addMany take a 2nd parameter, called 'alias'. This should be used when an object has more than one relationship with a single class. For example, adding an Owner and Seller relationships, which are both User objects:


This helps xPDO differentiate between which object belongs to which relationship.


Objects with one-to-many relationships can also be batch added via the addMany method. Let's say we want to add all the Wheel objects with width of 10 to our Car:

$wheels = $xpdo->getCollection('Wheel',array(
   'width' => 10,


This will add all the 10-width Wheels and save the relationships.

See Also