conditional repository injection - Spring Boot

Another attempt to solve this problem.

Based on the property, the autowired customRepository will be an instance of SimpleMongoRepository or SimpleCouchRepository.

    public interface CustomRepository extends CrudRepository<User, Long> {
        User findByLastName(String lastName); //custom methods
    }

    @Qualifier("specificRepo")
    @ConditionalOnProperty("mongo.url")
    public interface UserRepositoryMongo extends MongoRepository<User, Long>, CustomRepository{
    }

    @Qualifier("specificRepo")   
    @ConditionalOnProperty("couch.url")
    public interface UserRepositoryCouch extends  CouchbasePagingAndSortingRepository<User, Long>, CustomRepository{
    }

    public class UserService {

        @Autowired
        @Qualifier("specificRepo")
        private CustomRepository repository;
    }

We can use either ConditionalOnProperty or ConditionalOnExpression to switch between two different repository implementation.

1. If we want to control the autowiring with simple property presence/absence or property value, then ConditionalOnProperty can be used.

2. If complex evaluation is required, then we can use ConditionalOnExpression.

ConditionalOnProperty (presence/absence of a property)

@Qualifier("specificRepo")
@ConditionalOnProperty("mongo.url")
public interface UserRepositoryMongo extends MongoRepository<User, Long>{
}

@Qualifier("specificRepo")   
@ConditionalOnProperty("couch.url")
public interface UserRepositoryCouch extends  CouchbasePagingAndSortingRepository<User, Long>{
}

ConditionalOnProperty (based on value)

@ConditionalOnProperty("repo.url", havingValue="mongo", matchIfMissing = true) //this will be default implementation if no value is matching
public interface UserRepositoryMongo extends MongoRepository<User, Long> {
}

@ConditionalOnProperty("repo.url", havingValue="couch")
public interface UserRepositoryCouch extends  CouchbasePagingAndSortingRepository<User, Long> {
}

ConditionalOnExpression

@ConditionalOnExpression("#{'${repository.url}'.contains('couch')}")
public interface UserRepositoryCouch extends  CouchbasePagingAndSortingRepository<User, Long> {
}

UPDATE

Use CrudRepository/Repository type to inject based on your requirement.

public class DemoService {

    @Autowired
    @Qualifier("specificRepo")
    private CrudRepository repository;
}

Based on bean created, either UserRepositoryMongo or UserRepositoryCouch will be autowired. Make sure only one bean is instantiated to avoid ambiguity error.