service-guard

To validate microservice preconditions before a database mutation, implement an in-process service guard that reads the database and throws an error prior to executing any state changes. This ensures domain integrity by checking preconditions inside the same unit of work.

A service-layer guard in domain-driven design is a precondition check that reads the database within the same unit of work to verify an aggregate's state. It throws an error before any mutation occurs, preserving domain integrity by preventing invalid state transitions.

To add error handling for service preconditions, define a corresponding error constant and implement a guard that queries your repository. The guard reads the service's own aggregate within the transaction and throws the error before the mutation step begins.

No, you cannot use this service guard to check aggregates outside its own microservice. The guard runs inside the same unit of work and is restricted to only reading the service's own aggregate to validate preconditions before throwing.

To test service-layer guards for microservices, write tests that verify the guard queries the repository correctly and throws the defined error constant when preconditions fail. Testing must confirm the guard executes before the mutation step within the unit of work.

You need a database read for microservice error handling when validating preconditions before a mutation. By reading the service's own aggregate inside the same unit of work, the guard checks current state and throws to prevent invalid data changes.