Raise a ValidationError on bad JSON in Field.to_python

Author: Tim Heap

postgres_composite_types/__init__.py

@@ -40,6 +40,7 @@
 import sys
 from collections import OrderedDict
 
+from django.core.exceptions import ValidationError
 from django.db import migrations, models
 from django.db.backends.postgresql.base import \
     DatabaseWrapper as PostgresDatabaseWrapper
@@ -112,6 +113,10 @@ class BaseField(models.Field):
 
     Meta = None
 
+    default_error_messages = {
+        'bad_json': "to_python() received a string that was not valid JSON",
+    }
+
     def db_type(self, connection):
         LOGGER.debug("db_type")
 
@@ -144,7 +149,13 @@ def to_python(self, value):
         # is called with a string, assume it was produced by value_to_string
         # and decode it
         if isinstance(value, str):
-            value = json.loads(value)
+            try:
+                value = json.loads(value)
+            except ValueError:
+                raise ValidationError(
+                    self.error_messages['bad_json'],
+                    code='bad_json',
+                )
             return self.Meta.model(**{
                 name: field.to_python(value.get(name))
                 for name, field in self.Meta.fields

tests/test_field.py

@@ -1,9 +1,11 @@
 """Tests for composite field."""
 
 import datetime
+import json
 from unittest import mock
 
 from django.core import serializers
+from django.core.exceptions import ValidationError
 from django.db import connection
 from django.db.migrations.executor import MigrationExecutor
 from django.test import TestCase, TransactionTestCase
@@ -164,6 +166,35 @@ def test_serialize(self):
         self.assertEqual(old.bounding_box,
                          new.bounding_box)
 
+    def test_to_python(self):
+        """
+        Test the Field.to_python() method interprets strings as JSON data.
+        """
+        start = datetime.datetime.now()
+        end = datetime.datetime.now() + datetime.timedelta(days=1)
+
+        field = NamedDateRange._meta.get_field('date_range')
+        out = field.to_python(json.dumps({
+            "start": start.isoformat(),
+            "end": end.isoformat(),
+        }))
+
+        self.assertEqual(out, DateRange(start=start, end=end))
+
+    def test_to_python_bad_json(self):
+        """
+        Test the Field.to_python() handles bad JSON data by raising
+        a ValidationError
+        """
+        field = NamedDateRange._meta.get_field('date_range')
+
+        with self.assertRaises(ValidationError) as context:
+            field.to_python("bogus JSON")
+
+        exception = context.exception
+        self.assertEqual(exception.code, 'bad_json')
+
+
 
 class TestOptionalFields(TestCase):
     """