Forwarding events to message broker / outbox table

[tqwewe]

Firstly, thanks for this library. What you guys are doing is so valuable!

I've followed the book guide and implemented the bank service with postgres persistent data.. my next question is: How should events be forwarded to an event broker for other services to subscribe to?

I'm aware of the outbox pattern approach, is there any recommended way I can accomplish this? One simple way I can think of is have a Query which forwards events. impl Query<BankAccount> for EventForwarder.

Thanks!

[serverlesstechnology]

My apologies for the late response. You're quite correct, a new Query is the correct place to put this.

This might look something like:

struct KafkaEventForwarder {
    client: KafkaProducer
}

#[async_trait]
impl Query<BankAccount> for KafkaEventForwarder {
    async fn dispatch(&self, aggregate_id: &str, events: &[EventEnvelope<BankAccount>]) {
        for event in events {
            let payload = serde_json::to_vec(&event.payload).expect("unable to serialized payload");
            let record = KafkaRecord::new()
                .with_key(aggregate_id)
                .with_payload(&payload);
            self.client.send(record).await;
        }
    }
}

[CumpsD]

A small follow-up question to this. I adopted this pattern to send the message to SNS, on the receiving end it looks like this:

{
  "Type" : "Notification",
  "MessageId" : "f5458878-95d1-5aad-82d9-d3d5edf775d9",
  "SequenceNumber" : "10000000000000027000",
  "TopicArn" : "arn:aws:sns:eu-central-1:xxx:dev-events.fifo",
  "Message" : "{\"CustomerDepositedMoney\":{\"amount\":1000.0,\"balance\":9000.0}}",
  "Timestamp" : "2022-09-27T22:15:02.834Z",
  "UnsubscribeURL" : "https://sns.eu-central-1.amazonaws.com/?Action=Unsubscribe&SubscriptionArn=arn:aws:sns:eu-central-1:xxx:dev-events.fifo:aab561d9-73b3-4cdf-b527-9cbfa357eb47"
}

I'm using this as a playground for the events:

#[derive(Debug, Clone, Serialize, Deserialize, PartialEq)]
pub enum BankAccountEvent {
    AccountOpened {
        account_id: String,
    },
    CustomerDepositedMoney {
        amount: f64,
        balance: f64,
    },
    CustomerWithdrewCash {
        amount: f64,
        balance: f64,
    },
    CustomerWroteCheck {
        check_number: String,
        amount: f64,
        balance: f64,
    },
}

But how do I convert the incoming JSON {"CustomerDepositedMoney":{"amount":1000.0,"balance":9000.0}} back into an event?

[CumpsD]

To answer my own question: Seems serde can do this out of the box :)

[davegarred]

@CumpsD that's correct! I'm leaning on serde to do a lot of the heavy lifting throughout this crate.