Correctly format JSON file - php

Question

I'm trying to create a JSON file which contains objects and an array. Yet I'm missing the [ ]-brackets. I don't really know the exact terms for these JSON parts, which makes finding a solution using Google incredibly hard. I'm also a fairly new PHP coder, so I'm still learning. Any help or tips are really appreciated!
Code to create the JSON file:
$db_export = [
'account' => [
'username' => $username,
'email' => $email
]
];
file_put_contents("output.json", json_encode($db_export, JSON_PRETTY_PRINT));
Which outputs as:
{
"account": {
"username": "test",
"email": "test#domain.com"
}
}
What it's supposed to be:
{
"account": [
{
"username": "test",
"email": "test#domain.com"
}
]
}

Answer 1

Adding [] characters will help. This creates an array inside the array.
$db_export = [
'account' => [[ // <--- Added
'username' => $username,
'email' => $email
]] // <--- Added
];
file_put_contents("output.json", json_encode($db_export, JSON_PRETTY_PRINT));
This is how you get the result you want.
Output :
{ "account": [ { "username": null, "email": null } ] }
I guess it was a little simple :)

Answer 2

I am adding this to explain what is going on with the original answer. You can find this same information in the json_encode php manual page, in the example sections.
With any simple PHP array, json_encode will transform the PHP array into a JSON array:
$simple = array('apple', 'banana', 'coconut');
echo json_encode($simple);
Returns:
["apple","banana","coconut"]
Any associative array will be turned into a json object {} and each associative key will become a property name.
$associative = array('breakfast' => 'apple', 'lunch' => 'banana', 'dinner' => 'coconut');
echo json_encode($associative);
Returns:
{"breakfast":"apple","lunch":"banana","dinner":"coconut"}
In your example, you have an array with an associative key 'account' that contains an array with 2 child elements, each with an associative key.
This is the reason json_encode() is turning your structure into json objects.
In #Smokie's answer, the addition of an extra parent array that is "simple" ie. not keyed with a name, causes json_encode (following it's simple transformation rules) to create a javascript array, which it then sticks the javascript object inside of.
$username = 'test user';
$email = 'foo#bar.com';
$db_export = [
'account' => [[ // <--- Added
'username' => $username,
'email' => $email
]] // <--- Added
];
var_dump($db_export);
Returns:
array(1) {
["account"]=>
array(1) {
[0]=>
array(2) {
["username"]=>
string(9) "test user"
["email"]=>
string(11) "foo#bar.com"
}
}
}
Here I use var_dump as a quick debugging tool to show what the PHP array looks like. The important thing to note is that 'account' is now an array(1) with one element ( the 0th element) that contains your original child array.
Presumably you need this because the assumption is that an account could have multiple accountname/email address pairs. If that isn't the case, I would question why you need to force a useless array. I personally don't see how an 'account' could have multiple username/email pairs associated with it.
With that said, this code should further illustrate how this all works, and why:
$username = 'test user';
$email = 'foo#bar.com';
$db_export = [
'account' => [[ // <--- Added
'username' => $username,
'email' => $email
]] // <--- Added
];
//Add another username/email pair to account
$db_export['account'][] = ['username' => 'test2 user', 'email' => 'test2#bar.com'];
echo json_encode($db_export, JSON_PRETTY_PRINT);
Returns:
{
"account": [
{
"username": "test user",
"email": "foo#bar.com"
},
{
"username": "test2 user",
"email": "test2#bar.com"
}
]
}