PHP array_push with key => value

Here is my code

foreach ($query1 as $post)
{
    foreach ($query2 as $data)
    {
        if ($post->post_id == $data->post_id)
        {
            // add all actions from a post to its array
            if (!isset($post->post_meta))
            {
                $post->post_meta = array( strtolower($data->post_meta_key) => $data->post_meta_value );
            }
            else
            {
                array_push( $post->post_meta[strtolower($data->post_meta_key)] = $data->post_meta_value );
            }
        }
    }
}

Im not sure how to fix the code. Im not getting the value, only the key, and a few errors.

array_push() expects at least 2 parameters, 1 given

It should print out something like this

 [0] => stdClass Object
        (
            [post_id] => 218
            [post_meta] => Array
                (
                    [flagged] => 0
                    [deleted] => 1
                )

        )