JPA: How to get entity based on field value other than ID?

Question

In JPA (Hibernate), when we automatically generate the ID field, it is assumed that the user has no knowledge about this key. So, when obtaining the entity, user would query

Answer 1

Using CrudRepository and JPA query works for me:

import org.springframework.data.jpa.repository.Query;
import org.springframework.data.repository.CrudRepository;
import org.springframework.data.repository.query.Param;

public interface TokenCrudRepository extends CrudRepository {

 /**
 * Finds a token by using the user as a search criteria.
 * @param user
 * @return  A token element matching with the given user.
 */
    @Query("SELECT t FROM Token t WHERE LOWER(t.user) = LOWER(:user)")
    public Token find(@Param("user") String user);

}

and you invoke the find custom method like this:

public void destroyCurrentToken(String user){
    AbstractApplicationContext context = getContext();

    repository = context.getBean(TokenCrudRepository.class);

    Token token = ((TokenCrudRepository) repository).find(user);

    int idToken = token.getId();

    repository.delete(idToken);

    context.close();
}