Joining rows in many-2-many tables - getting values from another table in a CMP grid

<?xml version="1.0" encoding="UTF-8"?>
    <model package="myshoppackage" baseClass="xPDOObject" platform="mysql" defaultEngine="MyISAM" version="1.1">
        <object class="MYshop" table="myshop_shops" extends="xPDOSimpleObject">
    		<field key="name" dbtype="varchar" precision="255" phptype="string" null="false" default="" />

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

             <composite alias="ShopProducts" class="MYshopProducts" local="id" foreign="shop" cardinality="many" owner="local" />
        </object>

    <object class="MYproduct" table="myshop_products" extends="xPDOSimpleObject">
        <field key="title" dbtype="varchar" precision="255" phptype="string" null="false" default="" />
        <field key="sku" dbtype="int" precision="20" attributes="unsigned" phptype="integer" null="false" default="0" />

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

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

        <composite alias="ShopProducts" class="MYshopProducts" local="id" foreign="product" cardinality="many" owner="local" />
    </object>

    <object class="MYshopProducts" table="myshop_shops_products" extends="xPDOObject">
        <field key="shop" dbtype="int" attributes="unsigned" precision="10" phptype="integer" null="false" index="pk" />
        <field key="product" dbtype="int" attributes="unsigned" precision="10" phptype="integer" null="false" index="pk" />

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

        <aggregate alias="Product" class="MYproduct" local="product" foreign="id" cardinality="one" owner="foreign" />
        <aggregate alias="Shop" class="MYshop" local="shop" foreign="id" cardinality="one" owner="foreign" />
    </object>
</model>

$productId = 1;
$shopNames = array();

$c = $modx->newQuery('MYshopProducts');
$c->sortby('Shop.name', 'ASC');
$c->where(
    array('product' => $productId)
);

$results = $modx->getCollectionGraph('MYshopProducts', {'Shop:{} }, $c);

foreach ($results as $result) {
   $shopNames[] = $results->Shop->get('name');
}