Predict and diagnose API failures

  • 5 minutes

These two short activities check your model of the failure patterns in this module before the knowledge check. Decide each answer before you read it.

Predict the outcome of a concurrency conflict

Two fulfillment coordinators open the same equipment request at the same moment. Both clients retrieve the record with the ETag W/"12345". Coordinator A saves first, sending a PATCH with If-Match: W/"12345", and the update succeeds.

  • Coordinator B then saves, sending a PATCH with the same If-Match: W/"12345" header. What does the Web API return?
  • Coordinator B's app uses the SDK for .NET instead, with ConcurrencyBehavior.IfRowVersionMatches on the UpdateRequest. What happens?
  • What should Coordinator B's code do next?
  • Coordinator B's app sends its PATCH with no If-Match header at all. What happens to Coordinator A's change?

Check your predictions:

  • 412 Precondition Failed. The record changed after B retrieved it, so the ETag no longer matches.
  • The SDK throws a fault with the code ConcurrencyVersionMismatch.
  • Re-retrieve the current record and decide how to reconcile the two changes. Retrying the same write fails the same way.
  • B's update succeeds and silently overwrites A's change, because nothing told Dataverse to check the version.

Diagnose an authentication failure

The external inventory service authenticates as a confidential client. For each symptom, decide which layer is rejecting the call, Microsoft Entra ID or Dataverse, and what you check first.

  • Token acquisition fails because the service requests a user_impersonation scope.
  • The service gets a token, but every call to Dataverse fails as if it has no access to any data.
  • The service can read device records, but every write to device fails.
  • Calls work for an hour, then fail every time the service resends the token it already has.

Check your diagnoses:

  • Entra ID. A service with no signed-in user requests the <environment-url>/.default scope, not the delegated user_impersonation scope.
  • Dataverse. Check that an application user exists for the app registration and has a security role assigned.
  • Dataverse. The application user's security role doesn't grant write access to device.
  • Token lifetime. The token expired. Re-acquire a fresh token before expiry instead of resending the stale one.

If any answer surprised you, reread the section it comes from before the knowledge check.