DynamoDB: fix: support top level lists for Dynamo Item to_json (#7380)

moto/dynamodb/models/dynamo_type.py

@@ -316,14 +316,20 @@ class Item(BaseModel):
         return sum(bytesize(key) + value.size() for key, value in self.attrs.items())
 
     def to_json(self) -> Dict[str, Any]:
-        attributes = {}
+        attributes: Dict[str, Any] = {}
         for attribute_key, attribute in self.attrs.items():
             if isinstance(attribute.value, dict):
-                attr_value = {
+                attr_dict_value = {
                     key: value.to_regular_json()
                     for key, value in attribute.value.items()
                 }
-                attributes[attribute_key] = {attribute.type: attr_value}
+                attributes[attribute_key] = {attribute.type: attr_dict_value}
+            elif isinstance(attribute.value, list):
+                attr_list_value = [
+                    value.to_regular_json() if isinstance(value, DynamoType) else value
+                    for value in attribute.value
+                ]
+                attributes[attribute_key] = {attribute.type: attr_list_value}
             else:
                 attributes[attribute_key] = {attribute.type: attribute.value}
 

moto/dynamodb/responses.py

@@ -964,12 +964,11 @@ class DynamoHandler(BaseResponse):
                 if len(changed) != len(original):
                     return changed
                 else:
-                    return [
+                    any_element_has_changed = any(
-                        self._build_updated_new_attributes(
+                        changed[index] != original[index]
-                            original[index], changed[index]
-                        )
                         for index in range(len(changed))
-                    ]
+                    )
+                    return changed if any_element_has_changed else original
             else:
                 return changed
 

tests/test_dynamodb/test_dynamodb_condition_expressions.py

@@ -3,6 +3,7 @@ from decimal import Decimal
 
 import boto3
 import pytest
+from botocore.exceptions import ClientError
 
 from moto import mock_aws
 
@@ -421,3 +422,153 @@ def test_condition_expression_with_reserved_keyword_as_attr_name():
 
     item = table.get_item(Key={"id": "key-0"})["Item"]
     assert item == {"id": "key-0", "first": {}}
+
+
+@mock_aws
+def test_condition_check_failure_exception_is_raised_when_values_are_returned_for_an_item_with_a_top_level_list():
+    # This explicitly tests for a failure in handling JSONification of DynamoType
+    # when lists are at the top level of an item.
+    # This exception should not be raised:
+    # TypeError: Object of type DynamoType is not JSON serializable
+
+    dynamodb_client = boto3.client("dynamodb", region_name="us-east-1")
+    dynamodb_client.create_table(
+        TableName="example_table",
+        KeySchema=[{"AttributeName": "id", "KeyType": "HASH"}],
+        AttributeDefinitions=[
+            {"AttributeName": "id", "AttributeType": "S"},
+        ],
+        BillingMode="PAY_PER_REQUEST",
+    )
+    record = {
+        "id": {"S": "example_id"},
+        "some_list": {"L": [{"M": {"hello": {"S": "h"}}}]},
+    }
+    dynamodb_client.put_item(
+        TableName="example_table",
+        Item=record,
+    )
+
+    with pytest.raises(ClientError) as error:
+        dynamodb_client.update_item(
+            TableName="example_table",
+            Key={"id": {"S": "example_id"}},
+            UpdateExpression="set some_list=list_append(some_list, :w)",
+            ExpressionAttributeValues={
+                ":w": {"L": [{"M": {"world": {"S": "w"}}}]},
+                ":id": {"S": "incorrect id"},
+            },
+            ConditionExpression="id = :id",
+            ReturnValuesOnConditionCheckFailure="ALL_OLD",
+        )
+
+    assert error.type.__name__ == "ConditionalCheckFailedException"
+    assert error.value.response["Error"] == {
+        "Message": "The conditional request failed",
+        "Code": "ConditionalCheckFailedException",
+    }
+    assert error.value.response["Item"] == {
+        "id": {"S": "example_id"},
+        "some_list": {"L": [{"M": {"hello": {"S": "h"}}}]},
+    }
+
+
+@mock_aws
+def test_condition_check_failure_exception_is_raised_when_values_are_returned_for_an_item_with_a_top_level_string_set():
+    # This explicitly tests for a failure in handling JSONification of DynamoType
+    # when string sets are at the top level of an item.
+    # These exception should not be raised:
+    # TypeError: Object of type DynamoType is not JSON serializable
+    # AttributeError: 'str' object has no attribute 'to_regular_json'
+
+    dynamodb_client = boto3.client("dynamodb", region_name="us-east-1")
+    dynamodb_client.create_table(
+        TableName="example_table",
+        KeySchema=[{"AttributeName": "id", "KeyType": "HASH"}],
+        AttributeDefinitions=[
+            {"AttributeName": "id", "AttributeType": "S"},
+        ],
+        BillingMode="PAY_PER_REQUEST",
+    )
+    record = {
+        "id": {"S": "example_id"},
+        "some_list": {"SS": ["hello"]},
+    }
+    dynamodb_client.put_item(
+        TableName="example_table",
+        Item=record,
+    )
+
+    with pytest.raises(ClientError) as error:
+        dynamodb_client.update_item(
+            TableName="example_table",
+            Key={"id": {"S": "example_id"}},
+            UpdateExpression="set some_list=list_append(some_list, :w)",
+            ExpressionAttributeValues={
+                ":w": {"SS": ["world"]},
+                ":id": {"S": "incorrect id"},
+            },
+            ConditionExpression="id = :id",
+            ReturnValuesOnConditionCheckFailure="ALL_OLD",
+        )
+
+    assert error.type.__name__ == "ConditionalCheckFailedException"
+    assert error.value.response["Error"] == {
+        "Message": "The conditional request failed",
+        "Code": "ConditionalCheckFailedException",
+    }
+    assert error.value.response["Item"] == {
+        "id": {"S": "example_id"},
+        "some_list": {"SS": ["hello"]},
+    }
+
+
+@mock_aws
+def test_condition_check_failure_exception_is_raised_when_values_are_returned_for_an_item_with_a_list_in_a_map():
+    # This explicitly tests for a failure in handling JSONification of DynamoType
+    # when lists are inside a map
+
+    dynamodb_client = boto3.client("dynamodb", region_name="us-east-1")
+    dynamodb_client.create_table(
+        TableName="example_table",
+        KeySchema=[{"AttributeName": "id", "KeyType": "HASH"}],
+        AttributeDefinitions=[
+            {"AttributeName": "id", "AttributeType": "S"},
+        ],
+        BillingMode="PAY_PER_REQUEST",
+    )
+    record = {
+        "id": {"S": "example_id"},
+        "some_list_in_a_map": {
+            "M": {"some_list": {"L": [{"M": {"hello": {"S": "h"}}}]}}
+        },
+    }
+    dynamodb_client.put_item(
+        TableName="example_table",
+        Item=record,
+    )
+
+    with pytest.raises(ClientError) as error:
+        dynamodb_client.update_item(
+            TableName="example_table",
+            Key={"id": {"S": "example_id"}},
+            UpdateExpression="set some_list_in_a_map.some_list=list_append(some_list_in_a_map.some_list, :w)",
+            ExpressionAttributeValues={
+                ":w": {"L": [{"M": {"world": {"S": "w"}}}]},
+                ":id": {"S": "incorrect id"},
+            },
+            ConditionExpression="id = :id",
+            ReturnValuesOnConditionCheckFailure="ALL_OLD",
+        )
+
+    assert error.type.__name__ == "ConditionalCheckFailedException"
+    assert error.value.response["Error"] == {
+        "Message": "The conditional request failed",
+        "Code": "ConditionalCheckFailedException",
+    }
+    assert error.value.response["Item"] == {
+        "id": {"S": "example_id"},
+        "some_list_in_a_map": {
+            "M": {"some_list": {"L": [{"M": {"hello": {"S": "h"}}}]}}
+        },
+    }