Could not safely identify store assignment for repository candidate interface

The error message “could not safely identify store assignment for repository candidate interface” indicates that there is an issue with the assignment of a store for a repository candidate interface.

In most cases, this error occurs when a candidate interface does not have a specific store assigned to it, or when the assignment is ambiguous. To resolve this issue, you need to ensure that the store assignment is clear and unambiguous.

Here’s an example to help illustrate the problem:

public interface UserRepository {
    // interface methods
}

public class JpaUserRepository implements UserRepository {
    // implement interface methods using JPA
}

public class MongoUserRepository implements UserRepository {
    // implement interface methods using MongoDB
}

public class UserService {
    private UserRepository userRepository;

    public UserService(UserRepository userRepository) {
        this.userRepository = userRepository;
    }
}

public class Main {
    public static void main(String[] args) {
        // Ambiguous store assignment
        UserRepository userRepository = new ???; // Which implementation to choose?

        UserService userService = new UserService(userRepository);
    }
}
    

In the example above, we have a UserRepository interface that is implemented by two different classes: JpaUserRepository and MongoUserRepository. The UserService class depends on a UserRepository instance to perform its operations. However, when creating a UserRepository instance in the Main class, it is unclear which implementation to choose, leading to the error message mentioned in the query.

To resolve this ambiguity, you need to be explicit about the store assignment. For example, you can use a dependency injection framework like Spring to configure and manage your repository instances. By specifying the desired implementation, the framework can provide the appropriate UserRepository instance to the UserService class.