Collection: lax the restrictions on mainItem.

django_etesync/migrations/0034_auto_20200415_1248.py

@@ -0,0 +1,19 @@
+# Generated by Django 3.0.3 on 2020-04-15 12:48
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('django_etesync', '0033_auto_20200317_2010'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='collection',
+            name='mainItem',
+            field=models.OneToOneField(null=True, on_delete=django.db.models.deletion.PROTECT, related_name='of_collection', to='django_etesync.CollectionItem'),
+        ),
+    ]

django_etesync/migrations/0035_auto_20200415_1259.py

@@ -0,0 +1,19 @@
+# Generated by Django 3.0.3 on 2020-04-15 12:59
+
+from django.db import migrations, models
+import django.db.models.deletion
+
+
+class Migration(migrations.Migration):
+
+    dependencies = [
+        ('django_etesync', '0034_auto_20200415_1248'),
+    ]
+
+    operations = [
+        migrations.AlterField(
+            model_name='collection',
+            name='mainItem',
+            field=models.OneToOneField(null=True, on_delete=django.db.models.deletion.SET_NULL, related_name='of_collection', to='django_etesync.CollectionItem'),
+        ),
+    ]

django_etesync/models.py

@@ -29,7 +29,7 @@ class Collection(models.Model):
                            max_length=44, validators=[UidValidator])
     version = models.PositiveSmallIntegerField()
     owner = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE)
-    mainItem = models.OneToOneField('CollectionItem', related_name='of_collection', on_delete=models.PROTECT)
+    mainItem = models.OneToOneField('CollectionItem', related_name='of_collection', null=True, on_delete=models.SET_NULL)
 
     class Meta:
         unique_together = ('uid', 'owner')