validations.py

from tastypie.validation import FormValidation

class InstanceFormValidation(FormValidation):

    def is_valid(self, bundle, request=None):
        
        errors = {}
        data = bundle.data
        instance = bundle.obj

        if data is None:
            data = {}

        form = self.form_class(data, instance=instance)
        
        if not form.is_valid():
            errors.update(form.errors)

        return errors

class InstanceCleanedDataFormValidation(FormValidation):

    def is_valid(self, bundle, request=None):
        
        errors = {}
        data = bundle.data
        instance = bundle.obj

        if data is None:
            data = {}

        form = self.form_class(data, instance=instance)
        
        if form.is_valid():
            bundle.data = form.cleaned_data
        else:
            errors.update(form.errors)

        return errors