auto-incrementing ID on my JSON array - php

Question

I've been trying to do this for a while now and I just can't seem to get it right. One post got me very close but not quite there because my of JSON's hierarchy. (it's an assignment and this hierarchy is mandatory.)
What I do right now is submit info from one page, POST it to my php on another page, save it in an array there, json_encode that array and write that to my JSON file.
Here is my watered-down code, hopefully getting rid of most unnecessary code:
<?php
$filename = "json/exercises.json";
$filesize = filesize($filename);
$fp = fopen($filename, "r+");
#Accept the submitted form
$exLanguage = $_POST['exLanguage'];
$exTitle = $_POST['exTitle'];
$exStuff = $_POST['exStuff'];
#write to JSON with an incrementing ID
if (file_get_contents($filename) == "") {
$exercise = array (
"id" => 1,
"lang" => $exLanguage,
"title" => $exTitle,
"main_object" =>
[
"exStuff" => $exStuff
]
);
$exercise_json = json_encode($exercise, JSON_PRETTY_PRINT);
file_put_contents($filename, $exercise_json, FILE_APPEND);
} else {
#Get the last set ID
$jsonid = json_decode(fread($fp, $filesize), true);
$last = end($jsonid);
$title = prev($jsonid);
$lang = prev($jsonid);
$id = prev($jsonid);
$exercise = array (
"id" => ++$id,
"lang" => $exLanguage,
"title" => $exTitle,
"main_object" =>
[
"exStuff" => $exStuff
]
);
$exercise_json = json_encode($exercise, JSON_PRETTY_PRINT);
file_put_contents($filename, $exercise_json, FILE_APPEND);
}
?>
now what this does is if my json is empty it adds the first array correctly with the ID at 1. Then if I try to add to my json again it adds it correctly with the ID at 2. But any more attempted writes to the JSON will give me these errors:
Warning: end() expects parameter 1 to be array, null given
Warning: prev() expects parameter 1 to be array, null given
Warning: prev() expects parameter 1 to be array, null given
Warning: prev() expects parameter 1 to be array, null given
I tried doing a
$reset = reset($jsonid);
after writing to file but that didn't work, just gave me another error on the 3rd write for the reset being given a null too.
Can anyone please tell me how to get this too work? Or if there is a much easier way of getting this done?

Answer 1

Understand JSON format first. Its a collection of Objects which means attribute: value pair wrapped in {} and separated by comma , and then again wrapped in {} OR [] at top level.
Your JSON structure is incomplete or corrupted. What you are doing currently will create JSON in following format in your JSON file:
{ "id": 1, "lang": "as", "title": "asdsad" }
{ "id": 2, "lang": "as", "title": "asdsad" }
{ "id": 3, "lang": "as", "title": "asdsad" }
{ "id": 4, "lang": "as", "title": "asdsad" }
So json_decode will return null in this case because of invalid JSON format.
You need to keep appending your new JSON in existing JSON such that above format will become like this:
[
{ "id": 1, "lang": "as", "title": "asdsad" },
{ "id": 2, "lang": "as", "title": "asdsad" },
{ "id": 3, "lang": "as", "title": "asdsad" },
{ "id": 4, "lang": "as", "title": "asdsad" }
]
Which means your else block is incorrect. Use following code in else block:
$jsonid = json_decode(file_get_contents($filename), true);
$last = end($jsonid);
$id = $last['id'];
$jsonid[] = array (
"id" => ++$id,
"lang" => $exLanguage,
"title" => $exTitle,
"main_object" => array("exStuff" => $exStuff)
);
$exercise_json = json_encode($jsonid, JSON_PRETTY_PRINT);
file_put_contents($filename, $exercise_json, FILE_APPEND);
I hope you are not bound to use that incorrect/corrupted JSON format. That will not work with json_decode() in any case.