> To handle [compound primary keys] in DynamoDB, you would need to create two items in a transaction where each operation asserts that there is not an existing item with the same primary key.
There are other approaches--in cases where I've needed compound keys I've had success using version-5 UUIDs as the primary key constructed from a concatenation of the compound key fields. The advantage is that Dynamo's default optimistic locking works as expected with no transaction needed. A potential disadvantage is if you frequently need to look records up by just one component you'd need a secondary index instead of the primary doing double duty.
There are other approaches--in cases where I've needed compound keys I've had success using version-5 UUIDs as the primary key constructed from a concatenation of the compound key fields. The advantage is that Dynamo's default optimistic locking works as expected with no transaction needed. A potential disadvantage is if you frequently need to look records up by just one component you'd need a secondary index instead of the primary doing double duty.