Первичный ключ xPDOObject

<?xml version="1.0" encoding="UTF-8"?>
<model package="doodles" baseClass="xPDOObject" platform="mysql" defaultEngine="MyISAM" version="1.1">
	<object class="doodles" table="doodles" extends="xPDOSimpleObject" >

	<field key="title" dbtype="varchar" precision="255" phptype="string" null="false" default="" index="index" />
	<field key="description" dbtype="text" phptype="string" />

	<index alias="PRIMARY" name="PRIMARY" primary="true" unique="true">
		<column key="id" collation="A" null="false" />
	</index>

	</object>

	<object class="doodlesCategories" table="doodles_Categories" extends="xPDOSimpleObject">
		<field key="cid" dbtype="int" precision="11" phptype="integer" null="false" index="index" />
		<field key="did" dbtype="int" precision="11" phptype="integer" null="false" />

		<index alias="cid" name="cid" primary="false" unique="false" type="BTREE" >
			<column key="cid" length="" collation="A" null="false" />
			<column key="did" length="" collation="A" null="false" />
		</index>

		<aggregate alias="Resource" class="modResource" local="cid" foreign="id" cardinality="one" owner="foreign" />
		<aggregate alias="doodless" class="doodles" local="did" foreign="id" cardinality="one" owner="foreign" />
	</object>
</model>

<object class="modResource" table="modx_site_content" extends="xPDOSimpleObject">
		<field key="id" dbtype="int" precision="11" phptype="integer" null="false" index="index" />
		<composite alias="Resource" class="PageItem" local="id" foreign="resource_id" cardinality="many" owner="local" />
	</object>

public function parseConditions($conditions, $conjunction = xPDOQuery::SQL_AND) {

        $result= array ();
        $pk= $this->xpdo->getPK($this->_class);
        $pktype= $this->xpdo->getPKType($this->_class); // если у нас несколько primary key, то == Array

	... 
	if (is_array($conditions)) {
		// при remove и getObject - $conditions всегда integer или string
		...
		if (isset($conditions[0]) && is_scalar($conditions[0]) && !$this->isConditionalClause($conditions[0]) && is_array($pk) && count($conditions) == count($pk)) {
                $iteration= 0;
		// во прикол, кто так решил, что если у нас $conditions массив, то $pk обязательно массив,
		// а что по другому быть не может? (дебильно конечно но все же)
                foreach ($pk as $k) {...}
		...

	}
        elseif ($this->isConditionalClause($conditions)) {
            $result= new xPDOQueryCondition(array(
                'sql' => $conditions
                ,'binding' => null
                ,'conjunction' => $conjunction
            ));
        }
        elseif (($pktype == 'integer' && is_numeric($conditions)) || ($pktype == 'string' && is_string($conditions) && $this->isValidClause($conditions))) {
            if ($pktype == 'integer') {
                $param_type= PDO::PARAM_INT;
            } else {
                $param_type= PDO::PARAM_STR;
            }
            $field['sql']= $this->xpdo->escape($alias) . '.' . $this->xpdo->escape($pk) . ' = ?';
            $field['binding']= array ('value' => $conditions, 'type' => $param_type, 'length' => 0);
            $field['conjunction']= $conjunction;
            $result = new xPDOQueryCondition($field);
        }
        return $result;

<index alias="PRIMARY" name="PRIMARY" primary="true" unique="true" type="BTREE">
		<column key="id" length="" collation="A" null="false" />
		<column key="res_id" length="" collation="A" null="false" />
	</index>