JPA EntityManager查询--使用原生sql查询

Posted 2022-12-02 dream_heheda

SQL查询多个字段

query.getResultList() 返回List类型，每个对象类型是Obejct类型的数组。List<Object[]>

import java.math.BigDecimal;
import java.util.List;
 
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;
 
public class JpaDemoTest 
    @PersistenceContext
    private EntityManager em;
 
    public void testJpaNativeQuery() 
 
        BigDecimal classNo = null;     
        BigDecimal studentNo = null;
        String remark = null;
     
        String sql = "select t.class_no ,t.student_no ,t.remark   from t_student t where t.class_no =:class_no ";
        Query query = em.createNativeQuery(sql);
        query.setParameter("class_no", 20);
        //返回Object[] 类型的List
        List objecArraytList = query.getResultList();
        for (int i = 0; i < objecArraytList.size(); i++) 
            //每个结果是Obect[] 类型
            Object[] obj = (Object[]) objecArraytList.get(i);
            classNo = (BigDecimal) obj[0];
            studentNo = (BigDecimal) obj[1];
            remark = (String) obj[2];
        
        System.out.println("classNo==" + classNo + ";studentNo==" + studentNo + ";remark==" + remark);
    
 

SQL查询一个字段

query.getResultList() 返回List类型，每个对象类型是Obejct。List<Object>

import java.math.BigDecimal;
import java.util.List;
 
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;
import javax.persistence.Query;
 
public class JpaDemoTest 
    @PersistenceContext
    private EntityManager em;
 
    public void testJpaNativeQuery() 
 
        BigDecimal classNo = null;     
     
        String sql = "select t.class_no  from t_student t where t.class_no =:class_no ";
        Query query = em.createNativeQuery(sql);
        query.setParameter("class_no", 20);
        //返回Object 类型的List
        List objecArraytList = query.getResultList();
        for (int i = 0; i < objecArraytList.size(); i++) 
            //每个结果是Obect类型
            classNo = (BigDecimal) objecArraytList.get(i);
        
        System.out.println("classNo==" + classNo );