JPA 原生SQ查询

参考文章

https://blog.csdn.net/coding_1994/article/details/84575943

https://blog.csdn.net/m0_37776094/article/details/78419669

import org.springframework.stereotype.Service;

import javax.persistence.EntityManager;
import javax.persistence.EntityManagerFactory;
import javax.persistence.PersistenceUnit;
import javax.persistence.Query;
import java.util.List;

@Service
public class GetCodeService {
    private EntityManagerFactory emf;

    @PersistenceUnit//使用这个标记来注入EntityManagerFactory
    public void setEntityManagerFactory(EntityManagerFactory emf) {
        this.emf = emf;
    }

    /**
     * @param
     * @return
     */
    public String getCode(Integer type) {

        EntityManager em = emf.createEntityManager();
        em.getTransaction().begin();
        Query query = null;
        //定义SQL，可以多个表关联查询
        String sql = "SELECT getCode(?1)";

        //创建原生SQL查询QUERY实例
        query =  em.createNativeQuery(sql);
        query.setParameter(1,type);

        //执行查询，sql语句执行的查询结果只有一列时就会出现该问题！
        // 当有多个列时用数组取没有问题，如果只有一列会默认为string或者其他类型！
        List<String> result = query.getResultList();

        em.close();

        return  result.get(0).toString();
    }
}