Validate objects when initialized

[markpeek]

Opening for @MattJaccino based on questions in another issue.

Not specific to WAFv2, but one thing that did strike me as odd was that resource objects can be successfully initialized without all of the required properties being given. I thought I remembered it erroring out in situations like that, or am I missing something. ?

I thought with a property defined as

class SomeProperty(AWSProperty):
    props: PropsDictType = {
        "Prop1": (TYPE, True),
        "Prop2": (TYPE, False),
    }

if you tried to initialize without defining Prop1, it would throw some kind of exception. It seems like you can initialize resource objects without including all of the required properties, or with none at all.

Was this always the case, or did something change? If not, could that potentially be a feature request?

[markpeek]

This has always been the case due to the initial design of troposphere allowing for a more getter/setter interface:

>>> instance = ec2.Instance("myinstance")
>>> instance.ImageId = "ami-951945d0"
>>> instance.InstanceType = "t1.micro"
>>> t.add_resource(instance)

But this does bring up the point on whether validation could be done at object creation or when added to a template.

[MattJaccino]

Hi Mark,

I looked through the code and found there is a method of the BaseAWSObject called .validate(), but there is no code to run

    def validate(self) -> None:
        pass

but there is a different method called ._validate_props()

    def _validate_props(self) -> None:
        for k, (_, required) in self.props.items():
            if required and k not in self.properties:
                rtype = getattr(self, "resource_type", type(self))
                title = getattr(self, "title")
                msg = "Resource %s required in type %s" % (k, rtype)
                if title:
                    msg += " (title: %s)" % title
                raise ValueError(msg)

I see the validation bool defaults to True, so that those methods get run when converting to a dict, so maybe that .validate() method should call the validation methods for properties and title (if applicable), or maybe just for the properties.

I don't know, just an idea. Will work with the ._validate_props() method for now :)