NetworkError: 500 Internal Server Error in Ajax $post request - php

Question

I am trying to create a chat box and performing this AJAX post in Codeigniter but for some reason I am getting a server 500 internal server error and no response at all when I use firebug? Can anyone help?
This is my Javascript code
$(document).ready(function(){
$("a#submit").click(function(){
var chat_message_content = $("input#chat").val();
if(chat_message_content == ""){
return false;
}
$.post(base_url + "index.php/abovetheblues/add_chat_messages", {
chat_message_content : chat_message_content,
user_id : user_id
},
function(data){
alert(data);
},"json");
return false;
});
return false;
});
This is my controller
function add_chat_messages() {
// Grab the $chat_message_content, $user_id
$user_id = $this->input->post($this->session->userdata("user_id"));
$chat_message_content = $this->input->post('chat_message_content');
$this->abt_db->add_chat_message($user_id, $chat_message_content);
}
This is my model
function add_chat_message($user_id, $chat_message_content) {
$query_str = "INSERT INTO chat_message(user_id, chat_message_content) VALUES (?,?,?)";
$this->db->query($query_str, array($user_id, $chat_message_content));
}
And my view page
<script type="text/javascript">
var user_id = "<?php echo $this->session->userdata("user_id"); ?>";
</script>
<!--loads the header-->
<?php $this->load->view('abt-header'); ?>
<!--this is the login page-->
<div data-role="page" id="Abt-chat" data-add-back-btn="true">
<div data-role="header" data-position="fixed">
<h1>Peer Chat</h1>
</div>
<div data-role="content">
<div data-role="fieldcontain">
<div id="chat_viewport"></div>
<p>
<label>Input Chat: </label>
<input name="chat" id="chat" type="text" value=""/>
</p>
<p>
<?php echo anchor('#', 'Send Chat', array('title' => 'Send Chat', 'id' => 'submit')); ?>
</p>
</div>
<?php echo form_close(); ?>
</div>
</div>

Answer 1

You are passing user id as user_id. But while retrieving it in function you are doing mistake. Change it like below.
$user_id = $this->input->post('user_id');
And also -> need to be there before query()
$this->db->query($query_str, array($user_id, $chat_message_content));