DynamoDB: Use ON CONFLICT DO NOTHING clause on INSERT CDC operations

... to mitigate errors when events are relayed redundantly from retries
after partially failed batches on the Lambda processor.

CHANGES.md

@@ -2,6 +2,10 @@
 
 ## Unreleased
 - DynamoDB/Testing: Use CrateDB nightly again
+- DynamoDB: Use `ON CONFLICT DO NOTHING` clause on CDC operations
+  of type `INSERT`, to mitigate errors when events are relayed
+  redundantly from retries after partially failed batches on the
+  Lambda processor.
 
 ## 2024/10/09 v0.0.21
 - MongoDB: Fixed BSON decoding of `{"$date": 1180690093000}` timestamps

src/commons_codec/transform/dynamodb.py

@@ -201,7 +201,8 @@ def to_sql(self, event: t.Dict[str, t.Any]) -> SQLOperation:
                 f") VALUES ("
                 f":pk, "
                 f":typed, "
-                f":untyped);"
+                f":untyped) "
+                f"ON CONFLICT DO NOTHING;"
             )
             parameters = record.to_dict()
 

tests/transform/test_dynamodb_cdc.py

@@ -200,7 +200,7 @@ def test_decode_cdc_unknown_event(dynamodb_cdc_translator_foo):
 
 def test_decode_cdc_insert_basic(dynamodb_cdc_translator_foo):
     assert dynamodb_cdc_translator_foo.to_sql(MSG_INSERT_BASIC) == SQLOperation(
-        statement="INSERT INTO foo (pk, data, aux) VALUES (:pk, :typed, :untyped);",
+        statement="INSERT INTO foo (pk, data, aux) VALUES (:pk, :typed, :untyped) ON CONFLICT DO NOTHING;",
         parameters={
             "pk": {
                 "id": "5F9E-Fsadd41C-4C92-A8C1-70BF3FFB9266",
@@ -221,7 +221,7 @@ def test_decode_cdc_insert_basic(dynamodb_cdc_translator_foo):
 
 def test_decode_cdc_insert_nested(dynamodb_cdc_translator_foo):
     assert dynamodb_cdc_translator_foo.to_sql(MSG_INSERT_NESTED) == SQLOperation(
-        statement="INSERT INTO foo (pk, data, aux) VALUES (:pk, :typed, :untyped);",
+        statement="INSERT INTO foo (pk, data, aux) VALUES (:pk, :typed, :untyped) ON CONFLICT DO NOTHING;",
         parameters={
             "pk": {
                 "id": "5F9E-Fsadd41C-4C92-A8C1-70BF3FFB9266",