Django 2.0 support (#9)

* Travis config: Add Django 2.0

* Django 2.0: Add on_delete to ForeignKey fields

* Travis: Skip Python 3.2 and 3.3 for Django 2.0 too

* Accommodate Model.from_db_value() signature change in Django 2.0

This avoids a RemovedInDjango30Warning in Django 2.0.

Author: PiDelport

.travis.yml

@@ -14,6 +14,7 @@ python:
 
 env:
   - DJANGO="https://github.com/django/django/archive/master.tar.gz"
+  - DJANGO="django>=2.0,<2.1"
   - DJANGO="django>=1.10,<1.11"
   - DJANGO="django>=1.9,<1.10"
   - DJANGO="django>=1.8,<1.9"
@@ -52,6 +53,12 @@ matrix:
     # Django 1.11 requires Python 2.7, 3.4, or 3.5.
     # The Django 1.11.x series is the last to support Python 2.
     # The next major release, Django 2.0, will only support Python 3.5+
+    - python: "2.7"
+      env: DJANGO="django>=2.0,<2.1"
+    - python: "3.2"
+      env: DJANGO="django>=2.0,<2.1"
+    - python: "3.3"
+      env: DJANGO="django>=2.0,<2.1"
     - python: "3.2"
       env: DJANGO="https://github.com/django/django/archive/master.tar.gz"
     - python: "3.3"

tests/models.py

@@ -162,7 +162,8 @@ def get_other_model_timezone(obj):
 class ModelWithForeignKeyToTimeZone(models.Model):
     other_model = models.ForeignKey(
         to='tests.TZWithGoodStringDefault',
-        related_name='fk_to_tz'
+        related_name='fk_to_tz',
+        on_delete=models.CASCADE,
     )
     timestamp = LinkedTZDateTimeField(
         default=settings.TEST_DATETIME,
@@ -189,7 +190,8 @@ class ModelWithLocalTZCharField(models.Model):
 class TZTimeFramedModel(models.Model):
     other_model = models.ForeignKey(
         to='tests.TZWithGoodStringDefault',
-        related_name='fk_to_tz_too'
+        related_name='fk_to_tz_too',
+        on_delete=models.CASCADE,
     )
     start = LinkedTZDateTimeField(
         default=settings.TEST_DATETIME,

timezone_utils/fields.py

@@ -8,6 +8,7 @@
 import warnings
 
 # Django
+import django
 from django.core import checks
 from django.core.exceptions import ValidationError
 from django.db.models.fields import DateTimeField, CharField
@@ -83,15 +84,26 @@ def get_prep_value(self, value):
 
         return value
 
-    def from_db_value(self, value, expression, connection, context):    # noqa
-        """
-        Converts a value as returned by the database to a Python object. It is
-        the reverse of get_prep_value(). - New in Django 1.8
-        """
-        if value:
-            value = self.to_python(value)
-
-        return value
+    # Django 2.0 updates the signature of from_db_value.
+    # https://docs.djangoproject.com/en/2.0/releases/2.0/#context-argument-of-field-from-db-value-and-expression-convert-value
+    if django.VERSION < (2,):
+        def from_db_value(self, value, expression, connection, context):    # noqa
+            """
+            Converts a value as returned by the database to a Python object. It is
+            the reverse of get_prep_value(). - New in Django 1.8
+            """
+            if value:
+                value = self.to_python(value)
+            return value
+    else:
+        def from_db_value(self, value, expression, connection):
+            """
+            Converts a value as returned by the database to a Python object. It is
+            the reverse of get_prep_value(). - New in Django 1.8
+            """
+            if value:
+                value = self.to_python(value)
+            return value
 
     def to_python(self, value):
         """Returns a datetime.tzinfo instance for the value."""