Add startup check and support postgres (#10)

* Add startup check, support postgres

* Fix the version

oscar_odin/apps.py

@@ -18,3 +18,6 @@ def ready(self):
 
         # Register the Django model field resolver
         registration.register_field_resolver(ModelFieldResolver, Model)
+
+        # pylint: disable=W0611
+        from .checks import odin_startup_check

oscar_odin/checks.py

@@ -0,0 +1,23 @@
+from django import VERSION
+from django.core.checks import Error, register, Tags
+from django.conf import settings
+
+
+# pylint: disable=unused-argument
+@register(Tags.compatibility)
+def odin_startup_check(app_configs, **kwargs):
+    errors = []
+
+    django_major_version = VERSION[0]
+
+    if django_major_version < 4:
+        for _, database in settings.DATABASES.items():
+            if database["ENGINE"] == "django.db.backends.sqlite3":
+                errors.append(
+                    Error(
+                        "django-oscar-odin does not support sqlite3 with Django < 4. Please use engines that have can_return_rows_from_bulk_insert set to True (like Postgres) or upgrade your Django version to 4 or higher.",
+                        id="django-oscar-odin.E001",
+                    )
+                )
+
+    return errors

oscar_odin/utils.py

@@ -36,10 +36,12 @@ def in_bulk(self, instances, field_names):
     that ID. If `id_list` isn't provided, evaluate the entire QuerySet.
     """
 
-    batch_size = (
-        math.floor(connections[self.db].features.max_query_params / len(field_names))
-        - 1
-    )
+    max_query_params = connections[self.db].features.max_query_params
+
+    if max_query_params is not None:
+        batch_size = math.floor(max_query_params / len(field_names)) - 1
+    else:
+        batch_size = None
 
     if batch_size and batch_size < len(instances):
         qs = ()