php push an array into an existing array by it's index - php

Question

I'm having trouble with putting this question to words so ill just use a simple example, hope the title sortof got my problem across.
I'm creating a blog site where I can create blogposts and people can post comments. This is all saved in JSON except for login details which are saved in MySQL.
Now saving the blogposts go fine but I'm now trying to save comments.
Lets say the blogpost array looks like this:
Array
(
[0] => Array
(
[id] => 0
[title] => first blogpost
[content] => blogpost text
)
[1] => Array
(
[id] => 1
[title] => second blogpost
[content] => blogpost 2 text
)
)
Now someone writes a comment on 'second blogpost', I save it into an array like this(user taken from MySQL):
Array
(
[user] => myusername
[comment] => first post was better!
)
Now I want to merge them like this:
Array
(
[0] => Array
(
[id] => 0
[title] => first blogpost
[content] => blogpost text
)
[1] => Array
(
[id] => 1
[title] => second blogpost
[content] => blogpost 2 text
[comments] => Array
(
[user] => myusername
[comment] => first post was better!
)
)
)
I tried searching for a while and I'd expect this to be somewhere on the site already but I can't find it. I tried a couple variations of array_push and array_merge but it always ended up replacing the relevant blogpost instead of adding onto it.
EDIT: Someone noted the new array can't just float around, I think it's better now.

Answer 1

If you had any related key between posts and comments ( like having post_id in comment array ) that would make more sense to merge/put them.
I assume that's your blogpost
Array
(
[0] => Array
(
[id] => 0
[title] => first blogpost
[content] => blogpost text
)
[1] => Array
(
[id] => 1
[title] => second blogpost
[content] => blogpost 2 text
)
)
And your comments should be like:
Array
(
[user] => myusername
[comment] => first post was better!
[post_id] => 1
)
That way, you would be able to find the matched blogpost.
But, outside of your data structure, here is an example to merge an item into an element of an array of array.
A nested loop example.
foreach($posts as &$post){
foreach($comments as $comment){
if($post['id'] == $comment['post_id']){
$post['comments'][] = $comment;
}
}
}
the key here is sending each reference of the element into loop by &$post and then just manipulate them in loop.
Working with indexed arrays. (Like you already have index names as post_id and a comments index as an empty array)
foreach($comments as $comment){
$posts[$comment['post_id']]['comments'][] = $comment;
}

Answer 2

When the blogpost is updated, I assume you can get the id of that blogpost.
Then you can check if your data structure already has a key "comments". If it does not, add the key and create an array containing the comment and the user as the first array.
If it already exists, add a new array with the user and the comment so that there can be multiple comments for each blogpost.
For example using array_map:
$blogPosts = array_map(function ($blogPost) use ($blogPostId, $comment) {
if ($blogPost["id"] === $blogPostId) {
isset($blogPost["comments"]) ? $blogPost["comments"][] = $comment : $blogPost["comments"] = [$comment];
return $blogPost;
}
return $blogPost;
}, $blogPosts);
Php demo

Answer 3

So I fixed it after a bit of thinking
This is the final structure:
Array
(
[0] => Array
(
[id] => 0
[title] => 1st post
[content] => 1st post works!
[date] => 21-01-2019
[comments] => Array
(
[0] => Array
(
[user] => Me
[comment] => hey 1
[date] => 12:02 21-01-2019
)
[1] => Array
(
[user] => Me
[comment] => hey 2
[date] => 12:03 21-01-2019
)
)
)
)
I added a timestamp because of a suggestion here. It's also a simplified version of what I actually use, I tried adding many more comments and on multiple posts which both work.
This is the code, I should mention the ID is in the URL and it's saved as JSON:
$filename = file.json;
$currentArray = json_decode(file_get_contents($filename), true);
$comment = $_POST['comment'];
$username = $_SESSION['username'];
$date = date("H:i d-m-Y");
$id = $_GET['id'];
Pretty straightforward so far, here is how the array is created:
$currentArray[$id]["comments"][] = array (
'user' => $username,
'comment' => $comment,
'date' => $date
);
[$id] saves it to the correct post, ["comments"] saves it to the comments key(or creates it) and the last [] gives every comment a different index inside the ["comments"].
$newJSON = json_encode($currentArray, JSON_PRETTY_PRINT);
file_put_contents($filename, $newJSON);
And lastly encoding it and saving it to JSON.
Hope this helps someone.