How to get two id values from one select dropdown with PHP

I have one dropdown with a foreach loop which will pass to model using post method.

   <div class="form-group" ">
       <select class="form-control" id="rel" name="rl[][rel]" >
          <option></option>
          <?php
            foreach ($relationship as $row) {
                                            ?>
                <option value="<?php echo $row->relID; ?>"><?php echo $row->relCat; ?></option>
                 <?php
                     }
                       ?>
                   </select>
              </div>

and in the model it is getting the proper values using post method. As

$rel = $_POST['rel'];

Here the problem is when the user select one option ,I want to get two values like

 "<?php echo $row->relID; ?>" and "<?php echo $row->relCatID; ?>"

like

$rel = $_POST['rel']; //this for the $row ->relID
$relcat = $_POST['relcat'];//this for the $row ->relCatID

I want to get both from one selection without adding any visble dropdown or element..

Solution 1:

Try bellow code with ajax call

In Javascript code get value

var name = $('#rel option:selected').attr('data-cat_id');
var id = $('#rel').val();

<div class="form-group" >
  <select class="form-control" id="rel" name="rl[][rel]" >
    <option></option>
    <?php foreach ($relationship as $row) { ?>
      <option value="<?php echo $row->relID; ?>" data-cat_id="<?php echo $row->relCatID; ?>"><?php echo $row->relCat; ?></option>
    <?php } ?>
  </select>
</div>