0

I need some guidance in implementing mail notifications for new chat messages. The mail notification would inform the user of all the chats that had new messages in the previous hour.

To get it done, I'll need to query all chats in a table within a time interval. First thing that came to mind was adding new global index where a hash would be a boolean for whether the chat has unread messages, and range would be timestamp for the latest message within that chat.

But I have learned that boolean hash keys are quite the anti-pattern, as they would squeeze the documents in a single partition.

Is there a different model that would allow us to query all items in a table within a numeric range?

Improve this question
2
  • are you tried FilterExpression in scan? Commented Jan 17, 2019 at 10:13
  • @IftekharDani I wanna query the table, not scan it. Commented Jan 17, 2019 at 10:14

1 Answer 1

Reset to default
1

I’m assuming that you want to query unread messages for a given user, since (again) I’m assuming that the read/unread status of a given notification should not change for one user if another user reads a notification for the same thing.

Going on that assumption, you should use a sparse index with the userId (or equivalent) as the hashkey and unreadNotificationTime as the sort key. When you insert a new notification into your table, set the value of unreadNotificationTime to the time stamp for the notification. When the user has read the notification, delete the unreadNotificationTime attribute from the item.

Why does this work?

DynamoDB only requires that an item has the key attributes of the base table, and any other attributes are optional. The way indexes work in DynamoDB is that an item from the base table will only appear in an index of the item has all of the key attributes of that particular index.

By setting a value for unreadNotificationTime when you store a notification, all newly created notifications will automatically be populated to the unread messages index. By deleting the unreadNotificationTime when a message is read, you the notification from that index. With this schema, there’s no need for any filtering or scan operations. Your index will only contain notifications that are unread, grouped by userId, and sorted by date.

Improve this answer
Sign up to request clarification or add additional context in comments.

Comments

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.