JSON AJAX PHP loop array for SQL Statement

Question

Hope you can help me with this. I have an array that im sending over to my php script to process via ajax. What I want to do is loop through the array and based on the value of a certain key, execute a SQL statement for that array. Most of the time it will be multiple arrays. Here is what I got so far....for this example, ill put in static values:

HTML

    <form id='logForm' method='post' action='seatingProcess.php'>
    <span id='"219"' changeType='SEATCHANGE' setDeskId='9-4' prevSeatNew='T'></span>
    <span id='"229"' changeType='SEATCHANGE' setDeskId='2-5' prevSeatNew='T'></span>
    <span id='"299"' changeType='REMOVESEAT' setDeskId='0'></span>
<div class='btn btn-primary' type='submit' id='submit'>Submit</div>
    </form>

Javascript

$('#submit').click(function(){
            var spans = $('#logForm span');
            var data = [];

             $(spans).each(function(){
                 var newItem = {};
                 var item = $(this);
                 newItem.id = $(item).attr('id');
                 newItem.deskval = $(item).attr('setDeskId');
                 newItem.changeType = $(item).attr('changeType');
                 newItem.prevSeatNew = $(item).attr('prevSeatNew');
                 data.push(newItem);                 
             })

             $.ajax({
                 type: "POST",
                 url: "seatingProcess.php",              
                 data: {data:data},
                 success: function(msg){
                     console.log(msg); //testing the sql statements
                 },
                 error: function(){
                     alert('fail');                  
                 }               
             })

seatingProcess.php

<?php
if(isset($_POST['data'])){
 $obj = $_POST['data'];
 $doKeyChange = ['changeType'];
 $addValue = 'SEATCHANGE';
 $delValue = 'REMOVESEAT';  

 foreach($obj as $doKeyChange => $addValue) {
    //Array[0] {'id' => 219, 'deskval' => 9-4, 'prevSeatNew' => T}
   //Array[1] {'id' => 229, 'deskval' => 2-5, 'prevSeatNew' => T}

    $userid = ['id'];
    $desk_id = ['desk'];
    $set_desk_id = ['deskval'];
    $prevseat = ['prevSeat'];
    $prevseatNew= ['prevSeatNew'];
    $sqlAdd = "UPDATE roster SET  seat='$set_desk_id' preDesk='$prevseatNew' WHERE id='$userid'";
    print_r ($sqlAdd);
}
 foreach($obj as $doKeyChange => $delValue) {
    //Array[2]{'id' => 299, 'deskval' => 0}
    $userid = ['id'];
    $set_desk_id = ['deskval'];
    $sqlAdd = "UPDATE roster SET  seat='$set_desk_id' WHERE id='$userid'";
    print_r ($sqlAdd);
}
}
?>

Currently, im getting errors like:

Notice: Array to string conversion

Not sure what to do, thanks in advance

QUESTION

How do I write the php so that it takes the value of the requested key and puts it into the SQL statement?

This may be a stupid question but if you're using a form, why aren't you using inputs, even with hidden spans, then serializing the form itself? That would save a lot of js and guess work. — b3tac0d3
– b3tac0d3, Commented Nov 10, 2015 at 16:41
this code is a snippet of my much larger code. There's a reason for this way that makes sense with my main code but I understand how silly it looks in this example. If you could just indulge me with my example, id really appreciate it. — user247326
– user247326, Commented Nov 10, 2015 at 16:44
If the question is why you're getting array to string conversion errors, its because 'id' is a string but ['id'] is an array, so $userid = ['id']; gives you an array,....i.e. take the brackets off. — developerwjk
– developerwjk, Commented Nov 10, 2015 at 16:46
I made some updates, hopefully it can clarify what Im looking for — user247326
– user247326, Commented Nov 10, 2015 at 16:55

Mike Brant · Accepted Answer · 2015-11-10 19:31:45Z

You are currently making no attempt to serialize the data array into a format that can be properly handled by both $.ajax() and your PHP script. When you try to rely on jQuery's default object to query string conversion with code like this:

data: {data:data},

jQuery expects data to be an object (i.e. key-value pairs) that it can serialize into a query string. Passing a numerically indexed array as data is going to cause the conversion errors you are seeing.

You need to either properly create a serialized query string, or (and this would be my recommendation) since you are trying to pass a more complex data structure, you might consider JSON-encoding the data structure and POSTing to PHP with application/json header type. This would require you to then read the raw POSTed data in PHP, not read the data from $_POST, as PHP does not populate the $_POST superglobal for content type headers other than the form-encoded types.

To send JSON, your ajax call might look like this:

         $.ajax({
             type: "POST",
             url: "seatingProcess.php",
             contentType: "application/json",              
             data: JSON.stringify(data),
             success: function(msg){
                 console.log(msg); //testing the sql statements
             },
             error: function(){
                 alert('fail');                  
             }               
         })

In PHP you read the JSON from raw input like this:

$postdata = file_get_contents("php://input");
$request = json_decode($postdata);

I would like to give that a shot, Ive tried using the application/json header type but I could not get it to work. Can you show me what you mean exactly?
@user247326 I just updated the answer to show how to read JSON data from raw input in PHP.
Sorry to be a bother, im still a novice at this and im having a bit of trouble putting it together. How do i formulate the sending of the array?
@user247326 I have updated the answer to include modified $.ajax() call.

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