api: add better validation to EventGraceidField

gracedb/api/v1/events/fields.py

 from __future__ import absolute_import
 import logging
 
+from django.utils import six
+from django.utils.translation import ugettext_lazy as _
+
 from rest_framework import serializers
 
 from events.models import Event
@@ -11,10 +14,47 @@ logger = logging.getLogger(__name__)
 
 
 class EventGraceidField(GenericField, serializers.RelatedField):
+    default_error_messages = {
+        'invalid': _('Event graceid must be a string.'),
+        'bad_graceid': _('Not a valid graceid.'),
+    }
+    trim_whitespace = True
     to_repr = 'graceid'
-    lookup_field = 'id'
+    lookup_field = 'pk'
     model = Event
     queryset = Event.objects.all()
 
+    def _validate_graceid(self, data):
+        # data should be a string at this point
+        prefix = data[0]
+        suffix = data[1:]
+        if not prefix in 'GEHMT':
+            self.fail('bad_graceid')
+        try:
+            suffix = int(suffix)
+        except ValueError:
+            self.fail('bad_graceid')
+
+    def to_internal_value(self, data):
+        # Add string validation
+        if not isinstance(data, six.string_types):
+            self.fail('invalid')
+        value = six.text_type(data)
+        if self.trim_whitespace:
+            value = value.strip()
+
+        # Convert to uppercase (allows g1234 to work)
+        value = value.upper()
+
+        # Graceid validation
+        self._validate_graceid(value)
+
+        return super(EventGraceidField, self).to_internal_value(value)
+
     def get_model_dict(self, data):
         return {self.lookup_field: data[1:]}
+
+    def get_does_not_exist_error(self, graceid):
+        err_msg = "Event with graceid {graceid} does not exist.".format(
+            graceid=graceid)
+        return err_msg

gracedb/api/v1/fields.py

@@ -121,10 +121,14 @@ class GenericField(fields.Field):
         try:
             return self.model.objects.get(**model_dict)
         except self.model.DoesNotExist:
-            error_msg = '{model} with {lf}={data} does not exist' \
-                .format(model=self.model.__name__, lf=model_dict.keys()[0],
-                data=model_dict.values()[0])
-            raise exceptions.ValidationError(error_msg)
+            if hasattr(self, 'get_does_not_exist_error'):
+                err_msg = self.get_does_not_exist_error(data)
+            else:
+                err_msg = '{model} with {lf}={data} does not exist'.format(
+                    model=self.model.__name__, lf=model_dict.keys()[0],
+                    data=model_dict.values()[0]
+                )
+            raise exceptions.ValidationError(err_msg)
 
     def get_model_dict(self, data):
         return {self.lookup_field: data}