What is the best practice for querying an AWS Amplify GraphQL/DynamoDB database for changes since your last query?

Question

I have an iOS AWS Amplify Project using GraphQL API and DynamoDB to store data. This is a chat app.

Initially when a user signs in he will get all messages for a conversation. If then he comes back to the app a few days later I want to update any new messages in each conversation.

At the moment I am using the Date of the last message as a predicate for future queries. However I was wondering if there is a better or more standard way of querying a table for changes since the last time you queried?

I am not using DataStore. I am managing my own local storage.

let keys = Message.keys
let predicate = keys.conversationID == conversationID && keys.createdAt > lastQueryDate
Amplify.API.query(request: .paginatedList(Message.self, where: predicate, limit: 100)) { [weak self]
    DispatchQueue.main.async {
        switch event {
        case .success(let result):
            switch result {
            case .success(let messages):
                // handle data
            case .failure(let error):
                print("Got failed result with \(error.errorDescription)")
            }
        case .failure(let error):
            print("Got failed event with error \(error)")
        }
    }
}

score 0 · Answer 1 · answered Oct 30 '21 at 10:38

Querying based on the date of the last message is perfectly acceptable & standard.

DynamoDB itself doesn't provide a way to get "new" items (messages in this case) like you would be able to do using SQS for example - there's no way to "acknowledge" an item.

For pagination, you could use markers like ExclusiveStartKey however you already have a date field to filter by so there is absolutely no need to do so.

You're following best practices already by modeling your data correctly.

What is the best practice for querying an AWS Amplify GraphQL/DynamoDB database for changes since your last query?

1 Answers1