Populate form based on selected item php - php

Question

I have a page with a select list (gets successfully populated from mysql) and a text box. The text box has to be populated with a value from mysql based on the item selected in the list. But the ajax call to php is not working and i can not figure out what the issue is. I am just learning ajax and php, so a novice.. Please help. i am stuck with this for a long time.
<script>
$(document).ready(function() {
$('.selectpicker').on("change", function(){
var selected_data = $(this).find("option:selected").val();
alert(selected_data);
$.ajax ({
type: "POST",
data: { selected_data: selected_data },
url: "getoldcharity.php",
dataType: "json",
success: function(res) {
$('#charity_new').val(data.charity_new);
}
});
});
});
</script>
<form id="assign-fundraiser_form" class="form-horizontal" action="" method="post">
<div class="form-group">
<div class="col-md-3">
<select class="selectpicker form-control" id="fundraiser" name="fundraiser" required>
<option value="" selected disabled>Select a Fundraiser</option>
<?php
include('session.php');
$result1 = mysqli_query($db,"select concat(f_firstname,' ',f_lastname) fundraiser from fundraiser where f_company in (select contractor_name from contractor where company_name = '$_SESSION[login_user]') and f_status = 'Active' order by concat(f_firstname,' ',f_lastname)");
while ($rows = mysqli_fetch_array($result1))
{
echo "<option>" .$rows[fundraiser]. "</option>";
}
?>
</select>
</div>
</div>
<input type="text" name="charity" id="charity_new" />
</form>
<?php
include "session.php";
if (ISSET($_POST['.selectpicker'])) {
$ref = $_POST['.selectpicker'];
$query = $db->query("select f_charity charity_new from fundraiser limit 1");
$row = $query->fetch_assoc();
$charity_new = $row['charity_new'];
$json = array('charity_new' => $charity_new);
echo json_encode($json);
}
$db->close();
?>

Answer 1

There are a few problems that I've spotted from quick glance, so I've separated them below.
PHP
In your AJAX request, you are using data: { selected_data: selected_data } which means the PHP code will be expecting a POSTed key named selected_data but you're looking for .selectpicker. You seem to have mixed up a couple of things, so instead of:
$_POST['.selectpicker']
it should be:
$_POST['selected_data']
JavaScript
As Ravi pointed out in his answer, you also need to change your success function. The parameter passed through to this function is res not data, so instead of:
$('#charity_new').val(data.charity_new);
it should be:
$('#charity_new').val(res.charity_new);
MySQL
It also appears as though your query itself is invalid - you seem to be missing a comma in the column selection.
select f_charity charity_new from fundraiser limit 1
should be:
select f_charity, charity_new from fundraiser limit 1
or, seeing as you're not using the f_charity column in the results anyway:
select charity_new from fundraiser limit 1
You aren't using the value that is being POSTed either, meaning that whatever option is selected in the dropdown makes no difference to the query itself - it will always return the first record in the database.
Other
One other thing to be aware of is you're using a class selector on your change function. This means if you have multiple dropdowns with the same class name in your HTML, they will all be calling the same AJAX function and updating the textbox. I don't know if this is what you're aiming for, but from your code posted, you only have one dropdown in the form. If you only want that one dropdown to be calling the AJAX function, you should use an ID selector instead:
$('#fundraiser').on("change", function() {
// ...
}

Answer 2

I think, it should be
$('#charity_new').val(res.charity_new);
instead of
$('#charity_new').val(data.charity_new);