Verifying if entry exists in json array with php before posting to server

Question

I'm trying to figure out the best way to find a combination of values in a json array and if it exists, return an error message. If the combination of values is not present in the array, post them to the server. Here is what I have so far.

JSON

[{
  "username": "[email protected]",
  "contest": "TV",
  "timestamp": "Fri Nov 09 2018 16:33:38 GMT-0500 (Eastern Standard Time)"
}, {
  "username": "[email protected]",
  "contest": "Phone",
  "timestamp": "Fri Nov 09 2018 18:33:51 GMT-0500 (Eastern Standard Time)"
}]

I'm using ajax to post the details to php and that part works well.

        $.ajax({
            type: 'POST',
            url: 'update.php',
            data: { theuser: theuser, thecontest: thecontest, timestamp: timestamp },
            success: function() {
                //Show confirm notification hide btns and close the modal
                $('.modalbtns').hide();
                $('#successbox').fadeIn();
                setTimeout(function() {
                    $('#ModalCenter').modal('hide')
                }, 2400);
            },
            error: function() {
                // do something on error
            }
        });

This is what I have so far for the php (update.php)

<?php

$theuser = $_POST['theuser'];
$thecontest = $_POST['thecontest'];
$timestamp = $_POST['timestamp'];

if (is_writable('alldata.json')) {

    $json = file_get_contents('alldata.json');
    $data = json_decode($json);
    $data[] = array('username'=> $theuser, 'contest' => $thecontest, 'timestamp' => $timestamp);
    file_put_contents('alldata.json', json_encode($data));

} else {
    //echo "file is not writable, check permissions";
}

?>

For example what I'm trying to achieve is

Before posting, check in the json array if the following combination exists. username = [email protected] AND contest = Phone If it exists, return a custom message to the page e.g. (you already registered). If the combination is not in the json array, post to the file.

I believe it has to be something in the lines of

foreach($data as $item)
{
    if($item->username == $username) || ($item->contest == $contest){
        //combination found, do not post!
    }
}

But I can't get it to work, thanks for the help!

Where is the if($item->username == $username) || ($item->contest == $contest){? This sounds like a DB would be easier to use and manage as well. — user3783243
– user3783243, Commented Nov 12, 2018 at 17:05

Rajdeep Paul · Accepted Answer · 2018-11-12 17:24:11Z

1

You have to change the backend PHP code in the following way,

<?php
    $theuser = $_POST['theuser'];
    $thecontest = $_POST['thecontest'];
    $timestamp = $_POST['timestamp'];

    if (is_writable('alldata.json')) {
        $json = file_get_contents('alldata.json');
        $data = json_decode($json, true);
        $flag = false;
        foreach($data as $d){
            if($d['username'] == $theuser && $d['contest'] == $thecontest){
                $flag = true;
                break;
            }
        }
        if(!$flag){
            $data[] = array('username'=> $theuser, 'contest' => $thecontest, 'timestamp' => $timestamp);
            file_put_contents('alldata.json', json_encode($data));
        }else{
            // echo "you are already registered for the contest";
        }
    } else {
        // echo "file is not writable, check permissions";
    }
?>

Summary of needed changes:

Pass an additional argument true to json_decode() function to convert returned objects into associative arrays.
Assuming that a user can register for multiple contests, you should use && condition instead of || to check whether the user is already registered for a particular contest or not.
Use a boolean flag $flag and foreach loop to check if the user is already registered, display a simple message if already registered or attach the user data to json string if not registered.

edited Nov 12, 2018 at 17:24

answered Nov 12, 2018 at 17:15

Rajdeep Paul

16.9k3 gold badges21 silver badges39 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

Carlos27 Over a year ago

thanks, it works! How can I send the "you are already registered" string back to ajax?

Rajdeep Paul Over a year ago

@Carlos27, Your success callback function of AJAX would look something like this, success: function(data){alert(data);} where data is the returned data from server i.e. your echo statement.

Abhishek Sachan · Accepted Answer · 2018-11-12 17:16:44Z

0

You can simply create a function to do that check and use your loop code:

<?php
function check_combination($data){
    foreach($data as $item)
    {
        if($item->username == $username) || ($item->contest == $contest){
            return false; //if match found function will return by breaking the loop.
        }
    }
    return true; //it will be returned after all the values are iterated.
}


check_combination($data);

But please note if your data is too big this can be a performance issue, a better approach will be required.

answered Nov 12, 2018 at 17:16

Abhishek Sachan

2,3252 gold badges22 silver badges39 bronze badges

1 Comment

Carlos27 Over a year ago

You are right, I noticed that after getting close to 1000 entries (3 fields per entry) I got the following error in php.. [10-Dec-2018 14:42:21 UTC] PHP Warning: Invalid argument supplied for foreach() in /home/username/public_html/calendrier/update.php on line 10 And my json file got completely wiped. Is that really enough to create an issue with php? What do you suggest as a better approach?

Collectives™ on Stack Overflow

Verifying if entry exists in json array with php before posting to server

2 Answers 2

2 Comments

1 Comment

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

1 Comment

Your Answer

Sign up or log in

Post as a guest

Related