Use more obvious way to set current school on new objects.

biscuit/core/migrations/0011_default_school.py

+# Generated by Django 2.2.3 on 2019-07-30 21:02
+
+import biscuit.core.util.core_helpers
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('core', '0010_user_one_to_one'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='group',
+            name='school',
+            field=models.ForeignKey(default=biscuit.core.util.core_helpers.get_current_school, on_delete=django.db.models.deletion.CASCADE, to='core.School'),
+        ),
+        migrations.AlterField(
+            model_name='person',
+            name='school',
+            field=models.ForeignKey(default=biscuit.core.util.core_helpers.get_current_school, on_delete=django.db.models.deletion.CASCADE, to='core.School'),
+        ),
+    ]

biscuit/core/mixins.py

@@ -13,12 +13,6 @@ class SchoolRelatedManager(models.Manager):
         else:
             return qs.none()
 
-    def create(self, *args, **kwargs):
-        if 'school' not in kwargs:
-            kwargs['school'] = get_current_school()
-
-        return super().create(*args, **kwargs)
-
 
 class SchoolRelated(models.Model):
     class Meta:
@@ -26,4 +20,5 @@ class SchoolRelated(models.Model):
 
     objects = SchoolRelatedManager()
 
-    school = models.ForeignKey('core.School', on_delete=models.CASCADE)
+    school = models.ForeignKey(
+        'core.School', on_delete=models.CASCADE, default=get_current_school)