How to use PHP json_encode to format array data with [] - php

Question

Goal:
Use json_encode to format array data into a specified format
This is the needed format for the data after running through PHP json_encode:
NEEDED FORMAT
{
"top_level_data": [
{
"extension": {},
"sub_level_data1": 0
}
]
}
When I use this PHP:
$data = array('top_level_data' => array('extension' => array(),
'sub_level_data1' => 0
)
)
$data = json_encode($data);
I get this incorrect Output:
{
"top_level_data":{
"extension":[],
"sub_level_data1": 0
}
}
Question:
How can I modify my php to include the {} and the [] in the correct places as the Needed Format?

Answer 1

It's not clear how you're generating $data; if it's by the assignment you show then you can just add an extra layer of array at top_level_data, and cast the extension value to an object:
$data = array('top_level_data' => array(
array('extension' => (object)array(),
'sub_level_data1' => 0
)
)
);
If however you get the $data from another source, you can modify it like this:
$data['top_level_data']['extension'] = (object)$data['top_level_data']['extension'];
$data['top_level_data'] = array($data['top_level_data']);
Both methods yield this JSON:
{
"top_level_data": [
{
"extension": {},
"sub_level_data1": 0
}
]
}
Demo on 3v4l.org

Answer 2

json_encode will encode sequence array with []. The sequence array should has index from 0 to n. For other array, associative array and object will encoded with {}. Use the JSON_FORCE_OBJECT parameter of json_encode all the array will be encoded with {}.
Example:
echo json_encode(range(1,3)); // [1,2,3]
echo json_encode(array(2=>2)); // {"2":2}
echo json_encode(range(1,3),JSON_FORCE_OBJECT); // {"0":1,"1":2,"2":3}
echo json_encode((object)range(1,3)); // {"0":1,"1":2,"2":3}