Dynamodb batchgetItem API behavior for non existent keys - exception

Question

What is the behavior of DynamoDb BatchGetItem API if none of the keys exist in dynamodb?
Does it returns an empty list or throws an exception?
I am not sure about this after reading their doc: link
but I may be missing something.

Answer 1

BatchGetItem will not throw an exception. The results for those items will not be present in the Responses map in the response. This is also stated in the BatchGetItem documentation:
If a requested item does not exist, it is not returned in the result.
Requests for nonexistent items consume the minimum read capacity units
according to the type of read. For more information, see Capacity
Units Calculations in the Amazon DynamoDB Developer Guide.
This behavior is also easy to verify. This is for a Table with a hash key attribute named customer_id (the full example I am using is here):
dynamoDB.batchGetItem(new BatchGetItemSpec()
.withTableKeyAndAttributes(new TableKeysAndAttributes(EXAMPLE_TABLE_NAME)
.withHashOnlyKeys("customer_id", "ABCD", "EFGH")
.withConsistentRead(true)))
.getTableItems()
.entrySet()
.stream()
.forEach(System.out::println);
dynamoDB.batchGetItem(new BatchGetItemSpec()
.withTableKeyAndAttributes(new TableKeysAndAttributes(EXAMPLE_TABLE_NAME)
.withHashOnlyKeys("customer_id", "TTTT", "XYZ")
.withConsistentRead(true)))
.getTableItems()
.entrySet()
.stream()
.forEach(System.out::println);
Output:
example_table=[{ Item: {customer_email=jim#gmail.com, customer_name=Jim, customer_id=ABCD} }, { Item: {customer_email=garret#gmail.com, customer_name=Garret, customer_id=EFGH} }]
example_table=[]