Improve DDB transaction validation (#5521)

moto/dynamodb/exceptions.py

@@ -323,3 +323,12 @@ class InvalidConversion(JsonRESTError):
     def __init__(self):
         er = "SerializationException"
         super().__init__(er, "NUMBER_VALUE cannot be converted to String")
+
+
+class TransactWriteSingleOpException(MockValidationException):
+    there_can_be_only_one = (
+        "TransactItems can only contain one of Check, Put, Update or Delete"
+    )
+
+    def __init__(self):
+        super().__init__(self.there_can_be_only_one)

moto/dynamodb/models/__init__.py

@@ -32,6 +32,7 @@ from moto.dynamodb.exceptions import (
     StreamAlreadyEnabledException,
     MockValidationException,
     InvalidConversion,
+    TransactWriteSingleOpException,
 )
 from moto.dynamodb.models.utilities import bytesize
 from moto.dynamodb.models.dynamo_type import DynamoType
@@ -1656,6 +1657,11 @@ class DynamoDBBackend(BaseBackend):
 
         errors = []  # [(Code, Message, Item), ..]
         for item in transact_items:
+            # check transact writes are not performing multiple operations
+            # in the same item
+            if len(list(item.keys())) > 1:
+                raise TransactWriteSingleOpException
+
             try:
                 if "ConditionCheck" in item:
                     item = item["ConditionCheck"]
@@ -1682,6 +1688,7 @@ class DynamoDBBackend(BaseBackend):
                     item = item["Put"]
                     attrs = item["Item"]
                     table_name = item["TableName"]
+                    check_unicity(table_name, item)
                     condition_expression = item.get("ConditionExpression", None)
                     expression_attribute_names = item.get(
                         "ExpressionAttributeNames", None

tests/test_dynamodb/exceptions/test_dynamodb_exceptions.py

@@ -761,3 +761,42 @@ def test_query_begins_with_without_brackets():
         'Invalid KeyConditionExpression: Syntax error; token: "sk"'
     )
     err["Code"].should.equal("ValidationException")
+
+
+@mock_dynamodb
+def test_transact_write_items_multiple_operations_fail():
+
+    # Setup
+    table_schema = {
+        "KeySchema": [{"AttributeName": "id", "KeyType": "HASH"}],
+        "AttributeDefinitions": [{"AttributeName": "id", "AttributeType": "S"}],
+    }
+    dynamodb = boto3.client("dynamodb", region_name="us-east-1")
+    table_name = "test-table"
+    dynamodb.create_table(
+        TableName=table_name, BillingMode="PAY_PER_REQUEST", **table_schema
+    )
+
+    # Execute
+    with pytest.raises(ClientError) as exc:
+        dynamodb.transact_write_items(
+            TransactItems=[
+                {
+                    "Put": {
+                        "Item": {"id": {"S": "test"}},
+                        "TableName": table_name,
+                    },
+                    "Delete": {
+                        "Key": {"id": {"S": "test"}},
+                        "TableName": table_name,
+                    },
+                }
+            ]
+        )
+    # Verify
+    err = exc.value.response["Error"]
+    assert err["Code"] == "ValidationException"
+    assert (
+        err["Message"]
+        == "TransactItems can only contain one of Check, Put, Update or Delete"
+    )