CEL + Dapr - How do I access a property of a ServiceBusMessage as a filter in a YAML file

Question

I've been trying to use Dapr to route messages that are sent to a ServiceBusTopic to an API endpoints, but I can't seem to find the correct CommonExpressionLanguage syntax.

For example, if my message was something like:

{
  "key_for_filtering": "filter_value",
  "key_one": "value_one",
  "key_two": "value_two",
}

And my YAML file looked like:

apiVersion: dapr.io/v2alpha1
kind: Subscription
metadata:
  name: foo-bar-topic-subscription
spec:
  metadata:
    rawPayload: "true"
  pubsubname: servicebus-topic-pubsub
  topic: foo-sbt
  routes:
    rules:
    - match: key_for_filtering== 1
      path: /api/v1/upsert-account-settings
    - match: key_for_filtering== 2
      path: /api/v1/update-cosmos-transactions
    - match: key_for_filtering== 4
      path: /api/v1/update-external-credentials
scopes:
- foo-baz-scope

And I wished to route requests based on the key_for_filtering key, what do I have to use in order to properly route my messages as requests?

I have tried using self keyword, according to a Kubernetes doc about CommonExpressionLanguage but it did not work, I've been trying to find the correct syntax but can't seem to get it right.

I've also tried to use self.metadata and pass the values as metadata but couldn't find the solution this way.

Is this self and self.metadata syntax correct?

Answer 1

Looking at the YAML, maybe you need to check the configuration. If ‘key_for_filtering’ is expected to contain a string, then it should compare it to string values so make sure the data type matches.

match: event['key_for_filtering'] == 'filter_value1' path: /api/v1/upsert-account-settings

match: event['key_for_filtering'] == 'filter_value2' path: /api/v1/update-cosmos-transactions

match: event['key_for_filtering'] == 'filter_value3' path: /api/v1/update-external-credentials

Here , ‘event’ is the message sent to your ServiceBusTopic and make sure that the values on 'filter_value1', 'filter_value2' and 'filter_value3' match the string value of ‘key_for_filtering’.

For more info you may check these references.[1][2]

[1] https://docs.dapr.io/

[2] https://github.com/google/cel-spec