Question

Some of my PHP domain objects have properties which should be set from outside the object, but only by certain client objects. How can I go about enforcing this?

I am using setters within the class, and provided I can find a way to discriminate between different callers, I’m sure I could do some checking in the setter. This seems a bit convoluted though. I get the feeling that I’d be violating an OO design principle (perhaps “tell, don’t ask”?).

I imagine this is a reasonably common scenario. What am I missing?

Answer 1

It strikes me as a bad design in this case. You’d violate the single-responsibility principle of the class. Instead, refactor your code into more than one class, but use composition to attach optional properties.

For example:

class MyDataObject {
    private $main_property;
    private $extended_property;

    /* ... getters/setters for $main_property. */
    public function set_extended_property(IExtendedProperty $property) {
        $this->extended_property = $property;
    }
}

Where IExtendedProperty is an interface for the custom property data.