Intermittent 'Invalid JSON' error for DataTables table 'courses' in PHP project

Courses
1

Encountering intermittent DataTables JSON errors in my PHP project. Revised AJAX and PHP examples are provided below. Suggestions appreciated.

var gridInstance = $('#courseGrid').DataTable({
  processing: true,
  serverSide: true,
  ajax: {
    url: baseURL + 'admin/loadCourses',
    type: 'POST',
    dataType: 'json',
    data: {}
  },
  columns: [
    { data: 'courseID' },
    { data: 'courseName' },
    { data: 'courseStatus' }
  ]
});

public function loadCourses() {
  $cols = ['courseID', 'courseName'];
  $limit = $this->input->post('length');
  $offset = $this->input->post('start');
  $orderColumn = $cols[$this->input->post('order')[0]['column']];
  $total = $this->CourseModel->getTotalCount();
  $records = $this->CourseModel->fetchData($limit, $offset, $orderColumn, $this->input->post('order')[0]['dir']);
  echo json_encode([
    'draw' => intval($this->input->post('draw')),
    'recordsTotal' => $total,
    'recordsFiltered' => $total,
    'data' => $records
  ]);
}
2

I ran into a similar problem previously and discovered that the issue was partly due to how the PHP script was handling the output. I eventually found that setting the proper JSON content header with header(‘Content-Type: application/json’) at the start of the function helped clarify what was being sent back to DataTables. Additionally, I made sure that the SQL query and its results were always returning valid data, especially in edge cases where the data might be missing or unexpected, as that could lead to malformed JSON as well.

3

Hey SurfingWave, thanks for sharing the code! I had a similar issue a while back and it turned out that sometimes the culprit was a little sneaky unexpected output from PHP, maybe an extra whitespace or some warning before the JSON begins. Have you tried checking the PHP error log to see if there’s any hidden notice or deprecation warning? I added ob_clean(); at the beginning of my function, and it cleared up the problem for me. Also, I’m curious if you’re sure that all your AJAX post data is coming through correctly? I sometimes saw that intermittent problems were caused when some of the parameters weren’t passed as expected. What’s your experience been with this kind of bug? It would be cool to know if any particular part of the data retrieval steps seems to trigger the error. Cheers!

4

hey, maybe your issue comes from hidden warnings or file encoding probs. i once saw a stray newline in the start that broke my json. try disabling error_reporting or check your output buffering setup.