$small->addField('id', 'TS-BLK-S');
$small->addField('content_type', 'sku');
$small->addField('size', 'S');
$small->addField('inventory', 100);
$medium = new SolrInputDocument();
$medium->addField('id', 'TS-BLK-M');
$medium->addField('content_type', 'sku');
$medium->addField('size', 'M');
$medium->addField('inventory', 200);
$large = new SolrInputDocument();
$large->addField('id', 'TS-BLK-L');
$large->addField('content_type', 'sku');
$large->addField('size', 'L');
$large->addField('inventory', 300);
// add child documents
$product->addChildDocument($small);
$product->addChildDocument($medium);
$product->addChildDocument($large);
// or
// $skus = [$small, $medium, $large];
// $product->addChildDocuments($skus);
// add product document to the index
$updateResponse = $client->addDocument($product, true, 10000);
print_r($updateResponse->getResponse());
/* OUTPUT SIMILAR TO:
SolrObject Object
(
[responseHeader] => SolrObject Object
(
[status] => 0
[QTime] => 5
