DynamoDB ordered list

Question

I'm trying to store a List as a DynamoDB attribute but I need to be able to retrieve the list order. At the moment the only solution I have come up with is to create a custom hash map by appending a key to the value and converting the complete value to a String and then store that as a list.

eg. key = position1, value = value1, String to be stored in the DB = "position1#value1"

To use the list I then need to filter out, organise, substring and reconvert to the original type. It seems like a long way round but at the moment its the only solution I can come up with.

Does anybody have any better solutions or ideas?

Answer 1

I don't believe it is possible to store an ordered list as an attribute, as DynamoDB only supports single-valued and (unordered) set attributes. However, the performance overhead of storing a string of comma-separated values (or some other separator scheme) is probably pretty minimal given the fact that all the attributes for row must together be under 64KB.

(source: http://docs.amazonwebservices.com/amazondynamodb/latest/developerguide/DataModel.html)

Answer 2

The List type in the newly added Document Types should help.

Document Data Types

DynamoDB supports List and Map data types, which can be nested to represent complex data structures.

• A List type contains an ordered collection of values.
• A Map type contains an unordered collection of name-value pairs.

Lists and maps are ideal for storing JSON documents. The List data type is similar to a JSON array, and the Map data type is similar to a JSON object. There are no restrictions on the data types that can be stored in List or Map elements, and the elements do not have to be of the same type.

Answer 3

Add a range attribute to your primary keys.

Composite Primary Key for Range Queries

A composite primary key enables you to specify two attributes in a table that collectively form a unique primary index. All items in the table must have both attributes. One serves as a “hash partition attribute” and the other as a “range attribute.” For example, you might have a “Status Updates” table with a composite primary key composed of “UserID” (hash attribute, used to partition the workload across multiple servers) and a “Time” (range attribute). You could then run a query to fetch either: 1) a particular item uniquely identified by the combination of UserID and Time values; 2) all of the items for a particular hash “bucket” – in this case UserID; or 3) all of the items for a particular UserID within a particular time range. Range queries against “Time” are only supported when the UserID hash bucket is specified.