How to access a property of an object without knowing its name?

Question

PHP

Hello, such json comes from the database. The problem is that the names phone_lg, phone_samsung will always be different - how to access them in a loop without knowing them.

[{
  "id_predmet": "24",
  "json_param": {
    "phone_lg": {
      "price": "200",
      "old_price": "300"
    }
  }
}, {
  "id_predmet": "25",
  "json_param": {
    "phone_samsung": {
      "price": "400",
      "old_price": "500"
    }
  }
}]

$predmet = json_decode(JSON_WHAT_ABOVE); //take data from the database
foreach($predmet as $inv_field => $inv_val) {
echo $inv_val->json_param->phone_samsung->price;
}
If output directly ($inv_val->json_param->phone_samsung->price) - everything works. But I don't know the property names phone_lg, phone_samsung, etc. How to display data from an object if the names of their properties are not known?
I put a second loop inside foreach - the name displays and I can use it,
foreach($inv_val->json_param as $inv_field2 => $inv_val2) {
echo $inv_field2;
}
but there should be an easier way like: $inv_val->json_param->unknown->price. Tell me please

Answer 1

For example, you can collect unknown keys in a separate array and then take these values ​​from it:

$predmet = json_decode($json, true);

$keys = array_map(function ($n) {
    return array_keys($n['json_param'])[0];
}, $predmet);

$i = 0;
foreach ($predmet as $inv_val) {
    echo $inv_val['json_param'][$keys[$i]]['price'];
    $i++;
}

Answer 2

You can do this:

foreach($predmet as $inv_field => $inv_val) {
    $price = current((array) $inv_val->json_param)->price;
}

But it's really a crutch. At least it would be more correct to unify the keys and store the type of phone in another field instead of the key.