MySQL select multi dimensional? - php

Question

I would like to select all the posts and their attachments from my database.
This is the structure with dummy data:
Posts table
id | post | userId |
---------|---------------|----------|
1 | "hello" | 1 |
2 | "world" | 1 |
3 | "ouch" | 2 |
4 | "test" | 1 |
Attachments table
id | postId | fileName | time |
---------|---------------|----------|----------|
1 | 1 |"hey.jpg" | 0 |
2 | 1 |"test.png"| 53252354 |
3 | 2 |"asd.png" | 0 |
4 | 4 |"asd2.png"| 0 |
My code looks like this so far, but I doesn't really get what I'd like to.
$qry = $db->prepare('
SELECT p.id
, p.post
, p.userId
, att.fileName
, att.time
FROM posts p
LEFT
JOIN attachments att
ON att.postId = p.id
');
$qry->execute();
$postsArray = $qry->fetchAll(PDO::FETCH_ASSOC);
I would like to have something like this:
[{'id': 1,
'post': 'hello',
'userId': 1,
'attachments': [{'fileName': 'hey.jpg', 'time:' 0}, ... ]
}, ... ]
How could I achieve this?

Answer 1

Your query will give you the right data for the results you want, you can post-process in PHP to get the format you want:
foreach ($postArray as $post) {
$fixed_part = array('id' => $post['id'], 'post' => $post['post'], 'userId' => $post['userId']);
$key = serialize($fixed_part);
if (!isset($out[$key])) $out[$key] = $fixed_part;
$out[$key]['attachments'][] = array('fileName' => $post['fileName'], 'time' => $post['time']);
}
$out = array_values($out);
echo json_encode($out, JSON_PRETTY_PRINT);
Output is too long to post but can be seen in this demo. Query results can be seen on dbfiddle.

Answer 2

Usually I would do something like this:
$result = $db->query("select id, post, userId from posts");
$posts = [];
while ($post = $result->fetch(PDO::FETCH_OBJECT)) {
$post->attachments = [];
$posts[$post->id] = $post;
}
$result = $db->query("select postId, fileName, time from attachments");
while ($att = $result->fetch(PDO::FETCH_OBJECT)) {
$posts[$att->postId]->attachments[] = $att;
unset($att->postId); // optional
}
$posts = array_values($posts); // optional
echo json_encode($posts);
Note that the $posts array is id-indexed. I would keep it that way. But if you need exactly the same result as in your question (zero-indexed), you can add this line:
$posts = array_values($posts);
In newer MySQL versions you can also get the JSON result with a single SQL query:
select json_arrayagg(post_json) as json
from (
select json_object(
'id', p.id,
'post', p.post,
'userId', p.userId,
'attachments', json_arrayagg(
json_object('fileName', a.fileName, 'time', time)
)
) as post_json
from posts p
left join attachments a on a.postId = p.id
group by p.id
) x
Result:
[{"id": 1, "post": "hello", "userId": 1, "attachments": [{"time": 0, "fileName": "hey.jpg"}, {"time": 53252354, "fileName": "test.png"}]}, {"id": 2, "post": "world", "userId": 1, "attachments": [{"time": 0, "fileName": "asd.png"}]}, {"id": 3, "post": "ouch", "userId": 2, "attachments": [{"time": null, "fileName": null}]}, {"id": 4, "post": "test", "userId": 1, "attachments": [{"time": 0, "fileName": "asd2.png"}]}]
db-fiddle demo