EntityGetter

package metubeV2.repository.util;

import javax.persistence.EntityManager;
import javax.persistence.NoResultException;
import javax.persistence.criteria.CriteriaBuilder;
import javax.persistence.criteria.CriteriaQuery;
import javax.persistence.criteria.Root;
import java.util.Optional;

/**
 * Created by IntelliJ IDEA.
 * User: LAPD
 * Date: 7.2.2019 г.
 * Time: 10:07 ч.
 */
public class EntityGetter<T> {

     public static<T> Optional<?> getEntityByParameter(String name,
                                                   String parameterName,
                                                   EntityManager entityManager,
                                                   Class<T> aClass) {
        CriteriaBuilder criteriaBuilder = entityManager
                .getCriteriaBuilder();
        CriteriaQuery<T> criteriaQuery = (CriteriaQuery<T>) criteriaBuilder
                .createQuery(aClass.getClass());
        Root<T> root = (Root<T>) criteriaQuery.from(aClass.getClass());

        criteriaQuery.select(root)
                .where(criteriaBuilder
                        .equal(root.get(parameterName), name));

        try {
            return Optional.ofNullable(entityManager
                    .createQuery(criteriaQuery)
                    .getSingleResult());

        } catch (NoResultException ignored) {
            return Optional.empty();
        }
    }

}