Unable to use validators with PatchJSONParameters

I am not able to use the validates decorator using PatchJSONParameters.

For example, using the following code raise a ValueError (field does not exist) while there are fields in PATH_CHOICES.

@validates('name')
def validate_name(self, data):
    if len(data)<3:
        raise ValidationError('Too short!')

I am not even sure that this is an issue as I don’t know how I am supposed to do it. I can see there is already some code to map validators with patched fields in PatchJSONParameters.__init__:

self.fields['op'].validators = \
    self.fields['op'].validators + [validate.OneOf(self.OPERATION_CHOICES)]
self.fields['path'].validators = \
    self.fields['path'].validators + [validate.OneOf(self.PATH_CHOICES)]

[DurandA]

Thank you @frol for your support and detailed answers. 😃 You should get paid for this! The article from William Durand is indeed excellent reading. I think that the workaround is good enough.

I wish that your patches (especially marshmallow integration) will be merged into Flask-RESTPlus one day.

[frol]

@DurandA Please, read this short article on the PATCH matter: http://williamdurand.fr/2014/02/14/please-do-not-patch-like-an-idiot/. After you read it, you should understand that the classes inherited from PatchJSONParameters have only 3 (three) constant fields: op, path, and value. Thus, there won’t be any name field. You may try to use @validates_schema (it should work in theory, but I haven’t tried it myself):

@validates_schema
def validate_name(self, data):
   if data['op'] == 'replace' and data['path'] == '/name' and len(data['value']) < 3:
        raise ValidationError('Too short!', 'name')

NOTE: This is just a workaround since there must be a nicer way to implement this.