JPA EntityManager查询--使用原生sql 并且把查询结果转为实体对象

这篇文章主要记录 使用原生sql查询 并且把查询结果转为实体对象, 注意：这儿使用的数据库 是oracle数据库

这儿记录了三种查询：精确查询，模糊查询，分页查询。

1.把原生sql查询的结果转为实体类对象用的是 Query query = em.createNativeQuery(sql, Student.class);

 2.实体类 要使用@Entity 和 @Id 注解，否则会报错

新建实体类

import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class Student {
	@Id
	private Long classNo;
	private Long studentNo;
	private String remark;
	//省略了getter setter方法
	@Override
	public String toString() {
		return "RiskUnit [classNo=" + classNo + ", studentNo=" + studentNo + ", remark=" + remark + "]";
	}	 
}

1. 精确查询   where t.class_no = :class_no

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() {

		// sql
		String sql = "select t.class_no  classNo ,t.student_no studentNo ,t.remark remark  from t_student t where t.class_no = :class_no ";
		// 执行查询 并把结果专为实体类
		Query query = em.createNativeQuery(sql, Student.class);
		// 参数值
		query.setParameter("class_no", 400002);
		// 获取查询结果
		List students = query.getResultList();
		System.out.println("students===" + students.toString());
	}
}

2. 模糊查询    where t.class_no like '%'||:class_no||'%' "

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() {

		// sql
		String sql = "select t.class_no  classNo ,t.student_no studentNo ,t.remark remark  from t_student t where t.class_no like '%'||:class_no||'%' ";
		// 执行查询 并把结果专为实体类
		Query query = em.createNativeQuery(sql, Student.class);
		// 参数值
		query.setParameter("class_no", 400002);
		// 获取查询结果
		List students = query.getResultList();
		System.out.println("students===" + students.toString());
	}
}

3. 原生sql查询并分页  这里参考oracle sql 3.oracle sql 分页实现

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() {
		Integer pageNo = 2;
		Integer pageSize = 10;
		String sql = "select t.class_no  classNo ,t.student_no studentNo ,t.remark remark  from t_student t where t.class_no like '%' || :class_no || '%' order by t.class_no ";
		sql = " select * from ( select a.*, rownum as a_rownum from (" + sql + ") a where rownum <= "
				+ (pageNo + 1) * pageSize + ") b where b.a_rownum > " + pageNo * pageSize;
		Query query = em.createNativeQuery(sql, Student.class);
		query.setParameter("class_no", 40000);
		List students = query.getResultList();
 		System.out.println("student===" + students.toString()); 
	}
}

4. 有几种可能hibernate或者sql的报错：

1.Caused by: java.sql.SQLSyntaxErrorException: ORA-01747: invalid user.table.column, table.column, or column specification

 查询sql的字段名与数据库关键字冲突了，仔细查看sql 是因为where t.like 写错了

2.javax.persistence.PersistenceException: org.hibernate.MappingException: Unknown entity: com.mx.JpaDemo.entity.RiskUnit
需要在实体类RiskUnit上加上@Entity注解 

3.Caused by: org.hibernate.AnnotationException: No identifier specified for entity: com.mx.JpaDemo.entity.RiskUnit

需要在实体类加上@Id注解