how to use getNumRows() in Joomla after a second query - mysql

Question

I am developing a php script within the Joomla environment which queries the same table / database twice. Each time I need to know whether any matches are found.
It seemed that the best way would be to use the getNumRows(). The Joomla documentation is very specific on its use:
Miscellaneous Result Set Methods getNumRows()
getNumRows() will return the number of result rows found by the last
query and waiting to be read. To get a result from getNumRows() you
have to run it after the query and before you have retrieved any
results.
I follow this in my script. At the first query there is no problem, but the second query always throws up a warning - most likely because the getNumRows() call for the second time is after the retrieving results from the first query - which does not comply with the Joomla requirement.
Any ideas how to solve? Many thanks!
The part of my script in question reads:
$db = JFactory::getDBO();
$query = "SELECT * FROM #__art_mobiles WHERE user_agent_header='$ua'";
$db->setQuery($query);
$rowsAG = $db->getNumRows();
$replyAG = $db->loadRow();
if ($rowsAG == 0) {
//if no match check www.handsetdetection.com
//see https://www.handsetdetection.com/properties/vendormodel for current list of models in database together with headers
echo "not in local database - try external<br/>";
$prod = '';
if ($hd3->siteDetect()) {
$replyHD = $hd3->getReply();
$man = $replyHD['hd_specs']['general_vendor'];
$dev = $replyHD['hd_specs']['general_model'];
$os = $replyHD['hd_specs']['general_platform'];
echo "found in handsetdetection.com database<br/>";
//check for provisional match in local database
$query = "SELECT * FROM #__art_mobiles WHERE manufacturer='$man' AND device='$dev'";
$db->setQuery($query);
$rowsAGprov = $db->getNumRows();
$replyAGprov = $db->loadRow();
if ($rowsAGprov == 0) { **[ETC]**

Answer 1

I think this could be an issue with using $db->loadRow(); as getNumRows relies on an executed query.
For example you could try:
$db = JFactory::getDBO();
$query = "SELECT * FROM #__art_mobiles WHERE user_agent_header='$ua'";
$db->setQuery($query);
$replyAG = $db->query();
$rowsAG = $db->getNumRows();
And:
$query = "SELECT * FROM #__art_mobiles WHERE manufacturer='$man' AND device='$dev'";
$db->setQuery($query);
$replyAGprov = $db->query();
$rowsAGprov = $db->getNumRows();
Though I am not sure what/if the difference will be between the results returned from query and loadRow. It would be worth experimenting and seeing if this works.
Alternately, if you are only using getNumRows to see if a record exists, you could do some kind of check on your $replyAG variable instead. It again might be worth experimenting to see what loadRow returns if there are no results.

Answer 2

You need to add the following code before you write the the query:
$query = $db->getQuery(true);

Answer 3

You need to use
$db = JFactory::getDbo();
$query = $db->getQuery(true)
->select($db->qn(array('id')))
->from($db->qn('#__social_notifications'))
->where($db->qn('status') . ' = ' . $db->q(0));
$db->setQuery($query);
$db->execute();
$resultData = $db->getNumRows();