how can i create a success back function? - php

Question

$(function() {
$(".follow").click(function(){
var element = $(this);
var I = element.attr("id");
var info = 'id=' + I;
$.ajax({
type: "POST",
url: "listen.php",
data: info,
success: function(){}
});
$("#follow"+I).hide(); ///showing the remove button after the data has been entered
$("#remove"+I).show();
return false;
});
});
The PHP file listen.php
<?php session_start();
include_once ('includes/connect.php');
$id = $_POST['id'];
$follower = $_SESSION['user_id'];
$registerlistener = mysql_query("INSERT INTO relationships (leader, listener) VALUES('".$id."', '".$follower."')");
?>
what I want to do is when I click the follow button, I want to check if the data has been entered into the database, before showing the remove button, basically checking on the background.

Answer 1

mysql_query will return TRUE or FALSE. You can echo that from the PHP script, and have the ajax call read it.
listen.php:
<?php session_start();
include_once ('includes/connect.php');
$id = $_POST['id'];
$follower = $_SESSION['user_id'];
$registerlistener = mysql_query("INSERT INTO relationships (leader, listener) VALUES('".$id."', '".$follower."')");
echo json_encode(array('response'=>$registerlistener));
?>
In your JavaScript:
$.ajax({
type: "POST",
url: "listen.php",
data: info,
dataType: 'json',
success: function(data){
if(data.response){
// mysql_query returned TRUE
$("#follow"+I).hide();
$("#remove"+I).show();
}
else{
// FALSE
}
}
});
If you want, you can use the $.post shorthand:
$.post('listen.php', info, function(data){
if(data.response){
// mysql_query returned TRUE
$("#follow"+I).hide();
$("#remove"+I).show();
}
else{
// FALSE
}
}, 'json');

Answer 2

Put the code you want to execute inside your 'success' callback function.
$.ajax({
type: "POST",
url: "listen.php",
data: info,
success: function(){
$("#follow"+I).hide();
$("#remove"+I).show();
}
});

Answer 3

do it like this:
listen.php
<?php session_start();
include_once ('includes/connect.php');
$id = $_POST['id'];
$follower = $_SESSION['user_id'];
if($registerlistener = mysql_query("INSERT INTO relationships (leader, listener) VALUES('".$id."', '".$follower."')")):
echo "true";
else:
echo "false";
endif;
?>
pass parameter in success function, example "msg". whatever was echo'ed in listen.php will be in the msg variable now
success: function(msg){}
if(msg == "true")
{
//do something
}
else
{
//show error message
}
});