How to append unique ID to a json array - OctoberCMS / Laravel - php

Question

OctoberCMS BackendForm-Widget "Repeater" stores my data as an array in the database which looks like so:
{
"topic":"title",
"topic_description":"description",
}
{
"topic":"title",
"topic_description":"description",
}
I need to add a unique ID to each array so the json looks like this:
{
"topic_id":"1",
"topic":"title",
"topic_description":"description",
}
{
"topic_id":"2",
"topic":"title",
"topic_description":"description",
}
I have added this formBeforeSave function to my controller:
public function formBeforeSave($model)
{
$model->topics = array_map(array($model, 'topics'), function ($topic) {
$topic['id'] = uniqid();
});
}
But when trying to save the form OctoberCMS throws this error:
“array_map(): Argument #2 should be an array”
Adding this to the controller instead:
public function formBeforeSave($model)
{
$model->topics = array_map($model->topics, function ($topic) {
$topic['id'] = uniqid();
});
}
Throws the error:
array_map() expects parameter 1 to be a valid callback, array must have exactly two members
Has anyone experienced this and found a solution he/she could share please?

Answer 1

Each topic has a (unique) key already. So you could just copy this key as additional value while walking through the array:
// mocking test-data:
// $model->topics = [["topic"=>"title"], ["bar"=>"foo"]];
array_walk($model->topics, function(&$topic, $key) {
$topic['topic_id'] = $key;
});

Answer 2

As per the docs first argument should be callback, replace your code with following and try if it works.
public function formBeforeSave($model)
{
$model->topics = array_map(function ($topic) {
$topic['id'] = uniqid();
return $topic;
}, $model->topics);
}
Reference: http://php.net/manual/en/function.array-map.php

Answer 3

Applaus goes to LukeTower who pointed me to the right direction on Github.
The solution is putting the logic in the beforeSave() method on the model:
public function beforeSave()
{
$this->_FieldName_ = array_map(function ($miau) {
$miau['id'] = uniqid();
return $miau;
}, $this->_FieldName_);
}