AJAX post JSOSN data arrives empty - codeigniter

First I'd like to thank all responses.Actually it was a couple of mistakes,First: as @bipen said, data must be sent as an object rather than a string. and when I tried it, it didn't work because I didn't put the single-quote around data

$.ajax({  url: url,  type: 'POST',  contentType: 'application/json',  data: {'data': data}});

Second: as @foxmulder said, contentType was misspelled, and should be ContentTypeso the correct code is:

$.ajax({  url: url,  type: 'POST',  ContentType: 'application/json',  data: {'data': data}}).done(function(response){  alert('success');}).fail(function(jqXHR, textStatus, errorThrown){  alert('FAILED! ERROR: ' + errorThrown);});

and just FYI in case someone had issues with PHP fetching, this is how to do it:

$data = $this->input->post('data');    $data = json_decode($data);    $sum = $data->sum;    $info_obj = $data->info;    $item_qty = $info_obj[0]->quantity;

send your data as object and not string.. (not sure you have done that already unless we see you data's value.. if not then try it)

data = JSON.stringify(data);url = base_url + "index.php/home/make_order";        //alert(url);        var request = $.ajax({            url         : url,            type        : 'POST',            contentType : 'application/json',            data        : {data:data} //<------here        });        request.done(function(response){            alert('success');        });        request.fail(function(jqXHR, textStatus, errorThrown){            alert('FAILED! ERROR: ' + errorThrown);        });

updatedif as of comments you data is

 {"sum":"2.250","info":[{"id":"6","name":"bla","price":"1.000"}]}

then data:data is fine

 var request = $.ajax({            url         : url,            type        : 'POST',            contentType : 'application/json',            data        : data        });

bt you need to change your codeigniter codes to

 $this->input->post('sum') // = 2.250 $this->input->post('info')

contentType should be capitalized (ContentType)

see this question