Code concept of special classes

[safatshahin]

POC of special classes

[safatshahin]

This change creates a class for creating reference records and has the question manager handle the creation as a concept. If this change is good, I can start doing similar or related changes for special elements from questionlib and other parts of core_question.

[timhunt]

Safat, I think this is heading in the right direction, but there are serveral things that I would do differently.

1. I think question_references are sufficiently separate from questions, that I would have a manager class called question_refererence_manager to look after them. (We will probably need the name question_manager for something else later.)
2. public array $questionreference is a horrible way to store the data in the class. Why would you want to have to write $this->questionreference['usingcontextid'] instead of $this->usingcontextid? If you have separate fields, then each field can have the correct type specified, and a PHPdoc to explain what it means. For a key data object like the most important thing is for it to be easy for all developers to undersstand how this object represents the thing it represents.
3. I would put the crud operations on the manager class, rather than using something like the active record pattern on individual objects. (E.g. look at the file_storage API). This makes it pssible to have API methods like efficient bulk delete. Yes. No DB operations in the
4. I think for the references themselves, I think we need a class hierarchy like this:

class question_reference_location {
    public $usingcontext; // Make this the actual context object, I think.
    public $component;
    public $questionarea;
    public $itemid;
    public function __contruct($usingcontext, $component, $questionarea, $itemid) { ... }
    public function __toString() { ... } ... useful for debug display.
}
class question_reference extends question_reference_location {
    public $id;
    public $questionbankentryid;
    public $version;
    // Constructor, etc.
}
class question_set_reference extends question_reference_location {
    public $id;
    public $questionscontextid;
    public $filtercondition; // Should this be the JSON-decoded value?
    // Constructor, etc.
}

(https://github.com/moodleou/moodle-filter_embedquestion/blob/main/classes/embed_id.php is a similar class I created for something.)