How to call PHP function in dropdown menu? - php

Question

I want to call php function in dropdown menu by onchange event. I want with choose one of the options, the appropriate valuse are read from database and are list in another dropdown menu.
code:
<?php
function read() {
mysql_connect("localhost", "username", "password");
mysql_select_db("database_name");
$sql = mysql_query("SELECT name FROM table");
if (mysql_num_rows($sql)) {
$select = '<select name="select">';
while ($rs = mysql_fetch_array($sql)) {
$select.='<option value="' . '">' . $rs['name'] . '</option>';
}
}
$select.='</select>';
echo $select;
}
?>
<!--html code -->
<select onchange="document.write('<?php read(); ?>');">
<option value="0">a</option>
<option value="1">b</option>
<option value="2">c</option>
</select>
This code output:
My desired output:
How can I get My desired output ? Thanks

Answer 1

Just to explain:
PHP code is executed before the page is rendered in your user's browser (Server side).
In the other hand, Javascript is executed in the Client-side. It means that php finnished execution already.
If you wanna call a php function, you will have to make another request to the Server.
To do that "on the fly", you will have to use AJAX, as meantioned by #Jon in the comments.
Here is an example using jQuery (Just a javascript library, to simplify our task):
<script src="https://code.jquery.com/jquery-1.12.4.min.js"></script>
<script type="text/javasript">
//Listen to select 'onchange' event
$('select#your_select_id').change(function(){
//Read selected value
var inputValue = $(this).val();
//Make an ajax call
$.post('ajaxscript.php', { value: inputValue }, function(data){
//The return of 'read' function will be accessible trough 'data'
//You may create DOM elements here
alert('Finnished');
});
});
</script>
and here is our ajaxscript.php content:
<?php
//Declare (or include) our function here
//function read(){ ... }
$value = $_POST['value']; //Selected option
//...
echo read();

Answer 2

Hi You can also use javascript form submit in this and call a php function
<?php
function read() {
mysql_connect("localhost", "username", "password");
mysql_select_db("database_name");
$sql = mysql_query("SELECT name FROM table");
if (mysql_num_rows($sql)) {
$select = '<select name="select">';
while ($rs = mysql_fetch_array($sql)) {
$select.='<option value="' . '">' . $rs['name'] . '</option>';
}
}
$select.='</select>';
echo $select;
}
if (isset($_POST['value'])) {
read($_POST['value']);
}
?>
<form method="POST">
<select name="value" onchange="this.form.submit()">
<option value="0">a</option>
<option value="1">b</option>
<option value="2">c</option>
</select>
</form>