Codeigneitor data not inserted to the Database - php

Question

I have create form and i am trying to store the data using Ajax.but data is not inserted to the database.what can be the error.user_id will be auto increment. and also i want to validate sitename.it should restrict inserting same sitenames.
Here is my code
Controller
public function user_add()
{
$data_save = array(
"Mnumber" => $this->input->post("Mnumber"),
"email" => $this->input->post("email"),
"fname" => $this->input->post("fname"),
"address" => $this->input->post("address"),
"sitename" => $this->input->post("sitename"),
"title" => $this->input->post("title"),
"descr" => $this->input->post("descr")
);
if ($this->user_mod->AddUser($data_save)) {
echo "Successfully Saved";
} else {
echo "error";
}
}
}
Model
class user_mod extends CI_Model
{
public function AddUser($data_save)
{
if ($this->db->insert('users', $data_save)) {
return true;
} else {
return false;
}
}
}
View
<script>
function save_user_new() {
var user_id = $('#user_id').val();
var Mnumber = $('#Mnumber').val();
var email = $('#email').val();
var fname = $('#fname').val();
var address = $('#address').val();
var sitename = $('#sitename').val();
var title = $('#title').val();
var descr = $('#descr').val();
if (sitename != "" && Mnumber != "") {
$.ajax({
type: "post",
async: false,
url: "<?php echo site_url('form_con/user_add'); ?>",
data: { "user_id": user_id,
"Mnumber": Mnumber,
"email": email,
"fname": fname,
"address": address,
"sitename": sitename,
"title": title,
"descr": descr,
},
dataType: "html",
success: function (data) {
if (data == 'error') {
$('#success_msg').hide();
$('#error_msg1').show();
$('#error_msg1').html("Error : Something wrong.");
} else if (data == 'have') {
$('#success_msg').hide();
$('#error_msg1').show();
$('#error_msg1').html("Error : This Employee is already exists.");
} else {
$('#error_msg1').hide();
$('#success_msg').show();
$('#success_msg').html("Entitled leave successfully saved.");
$('#load_leave').html(data);
}
}
});
} else {
$('#success_msg').hide();
$('#error_msg1').show();
$('#error_msg1').html("Error : Please enter Employee Details.");
}
}
</script>
<form action="#">
<div class="form-body">
<div class="form-group">
<label class="control-label">Your First Name</label>
<input type="text" class="form-control" id="fname" name="fname" placeholder="Enter text">
<!--<span class="help-block"> A block of help text. </span>-->
</div>
<div class="form-group">
<label class="control-label">Email Address</label>
<div class="input-group">
<span class="input-group-addon">
<i class="fa fa-envelope"></i>
</span>
<input type="email" class="form-control" id="email" name="email" placeholder="Email Address">
</div>
</div>
<div class="form-group">
<label class="control-label">Your Mobile Number</label>
<input type="text" class="form-control" id="Mnumber" name="Mnumber" placeholder="Enter text">
<!--<span class="help-block"> A block of help text. </span>-->
</div>
<div class="form-group">
<label class="control-label">Your Address</label>
<input type="text" class="form-control" id="address" name="address" placeholder="Enter text">
</div>
<div class="form-group">
<label class="control-label">Your Site Name</label>
<input type="text" class="form-control" id="sitename" name="sitename" placeholder="Enter text">
<!--<span class="help-block"> A block of help text. </span>-->
</div>
<div class="form-group">
<label class="control-label">Title of Your Web site</label>
<input type="text" class="form-control" id="title" name="title" placeholder="Enter text">
</div>
<div class="form-group">
<label class="control-label">Description of Your Web Site</label>
<input type="text" class="form-control" id="descr" name="descr" placeholder="Enter text">
</div>
</div>
<div class="form-actions right">
<button type="submit" class="btn green" onclick="save_user_new()">Submit</button>
<button type="button" class="btn default">Cancel</button>
</div>
</form>