Support multiple/reusable top level validate methods

[jackqu7]

perhaps with hooks/decorator interface?

[krak3n]

Here is a complex validation example:

Password:

• Password Confirm if Password provided
• Password and Password Confirm must match if password provided
• Old password must be provided and valid if password provided

Email:

• Email Confirm Required if Email Provided
• Email and Email Confirm must match if Email Provided

If fields at validation were aware of the marshal data then this is fairly trivial to implement and can easily be reused with a single callable.

class RequiredIf(object):

    def __init__(self, field):
        self.field = field

    def __call__(self, value, data):
        if self.field in data:
            if value is None:
                raise ValidationError('This is required')

class FooSerializer(SQASerializer):
    __model__ = Foo

    foo = Field(t.String, required=False)
    bar = Field(t.String, required=False, extra_validators=[
        RequiredIf('foo')
    ])

Obviously this is quite a philosophical change for Kim, no field should ever be "aware" of another. Personally, I don't see a problem with a fields validators being "aware" of the data provided when marshalling for validation concerns.

I don't feel a top level validator in the serializer is the best place for this, mainly due to bug #29 but also it makes reuse quite tricky, yes you could have a common callable multiple serializers could use through inheritance, mixins etc, but personally I do not feel this is particularly elegant in this situation. A top level validation method should be a last resort for some really bespoke validation requirements imo.

Thanks,

Chris