I had a fiddle with it to see if I could work it out - and I did!
I added a recordset to get all entries in the relational table with that LenderID:
<?php
$rsCategories = new WA_MySQLi_RS("rsCategories",$Exclusives_i,1);
$rsCategories->setQuery("SELECT * FROM LenderCategories WHERE LenderCategories.LenderID = ?");
$rsCategories->bindParam("i", "".$_GET["LenderID"] ."", "-1"); //paramLender
$rsCategories->execute();
?>
then coded the checkbox like this:
<input type="checkbox" id="Filter" name="Filter[]" value="<?php echo($rsFilters->getColumnVal("FilterID")); ?>" <?php
$wa_startindex = 0;
while(!$rsCategories->atEnd()) {
$wa_startindex = $rsCategories->Index;
?><?php if ($rsCategories->getColumnVal("FilterID") == $rsFilters->getColumnVal("FilterID")) { // Show if ?>
checked <?php } // Show if ?><?php
$rsCategories->moveNext();
}
$rsCategories->moveFirst(); //return RS to first record
unset($wa_startindex);
unset($wa_repeatcount);
?> />
Sorted!