PHP OOP: Weird Array Return - php

Question

I have the following 'Course' class:
class Course {
// The constructor just sets the database object
public function __construct($mysqli) {
$this->mysqli = $mysqli;
}
public function getCourseInfoByID($id) {
$result = $this->mysqli->query("SELECT * FROM courses WHERE id='$id'");
$course_info = $result->fetch_array();
// If found, return the student object
if($course_info) {
return $course_info;
}
return FALSE;
}
}
When I declare the class and try to run the function "getCourseInfoByID", I get weird results (see below)
$cid = process_get_request('cid');
$course = new Course($mysqli);
if(! $course_info = $course->getCourseInfoByID($cid)) {
$error[] = "Invalid Course ID";
setError();
redirectTo("instructors.php");
}
print_r($course_info);
I get this:
Array ( [0] => 2 [id] => 2 [1] => 1 [course_type_id] => 1 [2] => 1 [instructor_id] => 1 [3] => Tooele [dz_name] => Tooele [4] => 4 Airport Road [dz_address] => 4 Airport Road [5] => Tooele [dz_city] => Tooele [6] => Utah [dz_state] => Utah [7] => 84020 [dz_zip] => 84020 [8] => [dz_email] => [9] => 2011-12-30 17:25:12 [created] => 2011-12-30 17:25:12 [10] => 2012-01-02 16:24:08 [start_date] => 2012-01-02 16:24:08 [11] => 2012-01-08 16:24:17 [end_date] => 2012-01-08 16:24:17 [12] => 10 [student_slots] => 10 [13] => Brett will also be assisting in teaching this course as Nathan's assistant. Brett paid Nathan quite well to be his assistant. [notes] => Brett will also be assisting in teaching this course as Nathan's assistant. Brett paid Nathan quite well to be his assistant. [14] => 0 [approved_by] => 0 [15] => 0000-00-00 00:00:00 [approved_on] => 0000-00-00 00:00:00 [16] => 0 [completed] => 0 )
Why is each record duplicated?

Answer 1

This is happening because you are returning both numeric and associative indexes. You should use fetch_assoc() or pass the appropriate constant MYSQLI_ASSOC or MYSQLI_NUM to return just those keys.
See documentation on mysqli_result::fetch_array().
As an aside I would type hint your constructor to force the passing of a mysqli class so you can't accidentally pass an invalid argument.

Answer 2

Read the docs for the fetch_array() method. The second parameter defaults to MYSQLI_BOTH.