At what stage of development is transaction support implemented in this project?

Transaction support in a project is usually implemented at the database interaction layer, i.e., in the Data Access Object (DAO) or Repository layer. This ensures the atomicity of operations when executing multiple related queries.

In Java, using Spring, transactions are often managed with the @Transactional annotation at the service layer or on methods that combine multiple database operations. This provides automatic transaction start, commit, or rollback.

Example:

@Service
public class UserService {

    @Transactional
    public void updateUserAndLog(User user) {
        userRepository.save(user);
        auditService.logChange(user);
    }
}

Thus, transaction support is implemented during the development of business logic that interacts with the database.