membershipworks: Avoid duplicating Transactions with NULL sid field

Treat NULL in Transaction.sid as non-distinct in the UNIQUE constraint

membershipworks/migrations/0006_remove_transaction_unique_sid_timestamp_and_more.py

@@ -0,0 +1,44 @@
+# Generated by Django 5.1.4 on 2024-12-06 19:44
+
+import itertools
+
+from django.db import migrations, models
+
+
+def remove_duplicates(apps, schema_editor):
+    Transaction = apps.get_model("membershipworks", "Transaction")
+    for _, group in itertools.groupby(
+        Transaction.objects.filter(sid=None), key=lambda t: t.timestamp
+    ):
+        dupes = list(group)
+        first_in_group = dupes.pop()
+        for t in dupes:
+            if any(
+                getattr(t, field.name) != getattr(first_in_group, field.name)
+                for field in Transaction._meta.get_fields()
+                if field.name != "id"
+            ):
+                raise Exception("Transaction doesn't match!")
+            t.delete()
+
+
+class Migration(migrations.Migration):
+    dependencies = [
+        ("membershipworks", "0005_historicalmember_nfc_card_number_and_more"),
+    ]
+
+    operations = [
+        migrations.RunPython(remove_duplicates, atomic=True),
+        migrations.RemoveConstraint(
+            model_name="transaction",
+            name="unique_sid_timestamp",
+        ),
+        migrations.AddConstraint(
+            model_name="transaction",
+            constraint=models.UniqueConstraint(
+                fields=("sid", "timestamp"),
+                name="unique_sid_timestamp",
+                nulls_distinct=False,
+            ),
+        ),
+    ]

membershipworks/models.py

@@ -377,7 +377,11 @@ class Transaction(BaseModel):
     class Meta:
         db_table = "transactions"
         constraints = [
-            models.UniqueConstraint("sid", "timestamp", name="unique_sid_timestamp")
+            models.UniqueConstraint(
+                fields=["sid", "timestamp"],
+                name="unique_sid_timestamp",
+                nulls_distinct=False,
+            )
         ]
 
     def __str__(self):