Multidimensional Array for JSON structure in PHP

Question

Recently I had some experience with converting mysql query results into json for a quiz system. Query results contain set of questions and related anwsers to them. The implemented procedure aims to put those questions and answers into multidimensional array and then convert it into json to build quiz db. I've ready to use JS procedure (quiz module) that works with below mentioned JSON structure. But to build this structure I'm stuck with the following php procedure:

Code in PHP:

$query = "SELECT s1.question, s2.answers, s2.correct
          FROM `questions` s1, `answers` s2
          WHERE s1.id=s2.questionid AND s1.courseid=".$_POST['courseid']."";
$result = mysqli_query($mysqli, $query) or die ("<b>Select failed:</b> ".mysqli_error($mysqli));

$final_quiz = array();
$final_quiz['introduction'] = "Introduction text goes here";
while ($rows = mysqli_fetch_assoc($result_quiz)) {
    $final_quiz['questions']['question'] = $rows['question'];
    $final_quiz['questions']['question']['answers'] = array($rows['answers'], "correct"=> $rows['correct']);
}
// convert to JSON
$json = json_encode($final_quiz);
echo $json;

Expected JSON Output:

{
    "introduction":"Some introductory text here",
    "questions":[
        {
            "question":"Question number one here?",
            "answers":["some incorrect answer", "a correct answer", "another incorrect answer"],
            "correct":1},   // indicates an array key that is relates to keys in "answers" 
        ...
    ]
}

How to organize multidimensional array in order to get above mentioned json structure? Any help would be appreciated.

UPDATES

The values in correct keys are indexes of the answers keys, i.e. if we have "correct":1 that would mean second value of answers key. Correct values for answers that come from MySQL are boolean (TRUE/FALSE). So, before putting all answers in answers_array_key as a set of answers one should remember newly assigned index array for the answer with TRUE value put that index array in correct_array_key as value. An example:

....
"answers":[0:"some incorrect answer", 1:"a correct answer", 2:"another incorrect answer"],
"correct":1},                      // this is correct answer key
....

Hope that will that will explain the idea of desired json sturcture mentioned above.

Umutcan Önal · Accepted Answer · 2014-11-12 12:49:28Z

1

I think this will produce the result you want.

while ($rows = mysqli_fetch_assoc($result_quiz)) {
    $final_quiz['questions'][]= array(
        'question' => $rows['question'],
        'answers' => array($rows['answers']), 
        'correct'=> $rows['correct']
    );
}

In your code, you are overwriting a single element of that array instead of appending the other questions

answered Nov 12, 2014 at 12:49

Umutcan Önal

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2 Comments

iLot Over a year ago

Looking at the json- I think you should append an object, not an array.

bofanda Over a year ago

In your solution it prints only first answer, but there are more than one answer for a given question. Also, the "correct" key should the same as correct "answer_key" in set of answers. Have a look in updated part of the question.

Marco Mura · Accepted Answer · 2014-11-12 12:39:41Z

0

You can try to use the php json_encode command. (link on php.net -> http://php.net/manual/it/function.json-encode.php)

The link show some example of array structure. On php.net it says it works with each type of structure (not resources).

Edit: as i see you already use this command, but how is the actual output? How much is different from your desired one?

answered Nov 12, 2014 at 12:39

Marco Mura

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2 Comments

bofanda Over a year ago

thanks for your response, but i need to put query result into multidimensional array "correctly" (while loop) in order to get above mentioned json structure.

bofanda Over a year ago

the result is different in answers arrays, namely only first option prints out and first correct key prints out. Have a look in UPDATED section of my question. I pt some clarifications

iLot · Accepted Answer · 2014-11-13 00:18:52Z

I believe this will solve it for you (I've used an array to test, I hope I got the question right).

You will need to change the foreach loop back to your while loop. I might have used a bit of different naming, you might need to change a thing or 2 to match your exact names:

<?php

$tmp = array (
    array("question"=> "this is a q", "answer"=>"incorrect", "correct" => false),
    array("question"=> "this is a q", "answer"=>"incorrect1", "correct" => false),
    array("question"=> "q1", "answer"=>"correct", "correct" => true),
    array("question"=> "q1", "answer"=>"incorrect", "correct" => false),
    array("question"=> "q1", "answer"=>"incorrect1", "correct" => false),
    array("question"=> "this is a q", "answer"=>"incorrect1", "correct" => false),
    array("question"=> "this is a q", "answer"=>"incorrect2", "correct" => false),
    array("question"=> "this is a q", "answer"=>"correct", "correct" => true),
    array("question"=> "this is a q", "answer"=>"incorrect3", "correct" => false)
);

$QAndA = array();
foreach ($tmp as $t){
    if (!isset($QAndA[$t['question']]['answers']))
        $QAndA[$t['question']]['answers'] = array();
    $QAndA[$t['question']]['answers'][] = $t['answer'];
    if ($t['correct'])
        $QAndA[$t['question']]['correct'] = count($QAndA[$t['question']]['answers']) -1;
}

foreach ($QAndA as $q => $data){
    $final_quiz['questions'][] = (object)array("question" => $q,
                                               "answers" => $data['answers'],
                                               "correct" => $data['correct']);

}
$json = json_encode($final_quiz);
echo $json;
?>

Result:

{
    "questions": [{
        "question": "this is a q",
        "answers": ["incorrect", "incorrect1", "incorrect1", "incorrect2", "correct", "incorrect3"],
        "correct": 4
    }, {
        "question": "q1",
        "answers": ["correct", "incorrect", "incorrect1"],
        "correct": 0
    }]
}

I do want to apologize for the naming conventions here and the somewhat brute attitude this code presents, but it is very late here;

Ashique C M · Accepted Answer · 2014-11-13 04:45:10Z

0

Add one counter $i and try the below code:

        $i = 0;
        while ($rows = mysqli_fetch_assoc($result_quiz)) {
        $final_quiz['questions'][$i] = array(
            'question' => $rows['question'],
            //'answers' => $rows['answers'], UPDATE THIS LINE
            'answers' => array(
                              '1' => $rows['answers'][1], 
                              '2' => $rows['answers'][2], 
                              '3' => $rows['answers'][3]) 
            // Why I started from index one? if index is consecutive from 0 to n 
            // will remove the index in JSON, so start indexing from 1 and make some changes in ur code

            'correct' => $rows['correct']
        );
        $i++;
        }

this will work

edited Nov 13, 2014 at 4:45

answered Nov 12, 2014 at 12:45

Ashique C M

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1 Comment

bofanda Over a year ago

Have a look to UPDATED part of the question please.

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