Question: Can you store lists in DynamoDB?

Answer

Yes. DynamoDB supports a native List type, so you can store an array without converting it into a JSON string. Lists preserve order, allow duplicate values and can contain different supported data types, including maps and other lists.

With the JavaScript document client, an attribute such as tags: ["new", "sale"] becomes a List. In the low-level API, the same value is {"L":[{"S":"new"},{"S":"sale"}]}. An empty list is valid.

You can update a list element by its zero-based index or append with list_append. To append when the attribute might be missing, use an expression such as SET #items = list_append(if_not_exists(#items, :empty), :newItems). Supply an empty array and the new array through the document client's value placeholders.

Use a Set instead when membership must be unique and order is irrelevant. Sets must contain one supported scalar type and cannot be empty.

The list shares the item's 400 KB size budget. A continuously growing event history is usually better stored as separate items with a common partition key and distinct sort keys. See data types and sort keys.

Source: AWS list and set types.