Single table design of a chat app on DynamoDB, checking if on the right direction

Question

I am all new to NoSQL and specifically DynamoDB single table design. Have been going through a lot of videos and articles on the internet regarding the single-table design and finally I have put together a small design for a chat application which I am planning to build in the future.

The access patterns I have so far thought about are -

1. Get user details by User Id.
2. Get list of conversations the user is part of.
3. Get list of messages the user has created
4. Get all members of a conversation
5. Get all messages of a conversation

Also want to access messages of a conversation by a date range, so far I haven't figured out that one.

As per the below design, if I were to pull all messages of a conversation, is that going to pull the actual message in the message attribute which is in the message partition?

Here is the snip of the model I have created with some sample data on. Please let me know if I am in the right direction.

Answer 1

As per the below design, if I were to pull all messages of a conversation, is that going to pull the actual message in the message attribute which is in the message partition?

No, it will only return the IDs of a message as the actual content is in a separate partition.

I'd propose a different model - it consists of a table with a Global Secondary Indexe (GSI1). The layout is like this:

Base Table:

• Partition Key: PK
• Sort Key: SK

Global Secondary Index GSI1:

• Partition Key: GSI1PK
• Sort Key: GSI1SK

Base Table

GSI 1

Access Patterns

1.) Get user details by User Id.

GetItem on Base Table with Partition Key = PK = U#<id> and Sort Key SK = USER

2.) Get list of conversations the user is part of.

Query on Base Table with Partition Key = PK = U#<id> and Sort Key SK = starts_with(CONV#)

3.) Get list of messages the user has created

Query on GSI1 with Partition Key GSI1PK = U#<id>

4.) Get all members of a conversation

Query on Base Table with Partition Key = PK = CONV#<id> and Sort Key SK starts_with(U#)

5.) Get all messages of a conversation

Query on Base Table with Partition Key PK = CONV#<id> and Sort Key SK starts_with(MSG#)

6.) Also want to access messages of a conversation by a date range, so far I haven't figured out that one.

DynamoDB does Byte-Order Sorting in a partition - if you format all dates according to ISO 8601 in the UTC timezone, you can make the range query, e.g.:

Query on Base Table with Partition Key PK = CONV#<id> and Sort Key SK between(MSG#2021-09-20, MSG#2021-09-30)