Truncate the syncqueue table before we add the unique constraint.

kolibri/core/device/migrations/0019_syncqueue_and_status.py

@@ -4,7 +4,7 @@
 
 import django.db.models.deletion
 import morango.models.fields.uuids
-from django.conf import settings
+from django.db import connection
 from django.db import migrations
 from django.db import models
 
@@ -20,6 +20,14 @@ class Migration(migrations.Migration):
             model_name="usersyncstatus",
             name="queued",
         ),
+        migrations.RunSQL(
+            [
+                "DELETE FROM device_syncqueue;"
+                if "sqlite" in connection.vendor
+                else "TRUNCATE TABLE device_syncqueue;"
+            ],
+            hints={"is_syncqueue": True},
+        ),
         migrations.AddField(
             model_name="syncqueue",
             name="attempts",

kolibri/core/device/models.py

@@ -483,9 +483,8 @@ def allow_relation(self, obj1, obj2, **hints):
 
     def allow_migrate(self, db, app_label, model_name=None, **hints):
         """Ensure that the SyncQueue models get created on the right database."""
-        if (
-            app_label == SyncQueue._meta.app_label
-            and model_name == SyncQueue._meta.model_name
+        if app_label == SyncQueue._meta.app_label and (
+            model_name == SyncQueue._meta.model_name or hints.get("is_syncqueue")
         ):
             # The SyncQueue model should be migrated only on the SYNC_QUEUE database.
             return db == SYNC_QUEUE