JPA(Java Persistence API)学习十六（JPQL基本操作）

1.概述

JPQL允许我们创建静态和动态查询。现在，我们将在下表中使用这两种查询来执行一些基本的JPQL操作。

2.JPQL动态查询示例

第一步：创建实体类StudentEntity

import javax.persistence.*;

@Entity
@Table(name = "student")
public class StudentEntity {

   @Id
   private int s_id;
   private String s_name;
   private int s_age;
}

第二步：配置xml

<?xml version="1.0" encoding="UTF-8"?>
   <persistence version="2.1"
   xmlns="http://xmlns.jcp.org/xml/ns/persistence"
   xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
   xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/persistence
http://xmlns.jcp.org/xml/ns/persistence/persistence_2_1.xsd">
   <persistence-unit name="Student_details">
   <class>com.yiibai.jpa.StudentEntity</class>
<properties>
   <property name="javax.persistence.jdbc.driver"
value="com.mysql.jdbc.Driver" />
   <property name="javax.persistence.jdbc.url"
value="jdbc:mysql://localhost:3306/testdb?serverTimezone=UTC" />
   <property name="javax.persistence.jdbc.user" value="root" />
   <property name="javax.persistence.jdbc.password"
value="123456" />
   <property name="eclipselink.logging.level" value="SEVERE" />
   <property name="eclipselink.ddl-generation"
value="create-or-extend-tables" />
</properties>
</persistence-unit>
   </persistence>

第三步：执行

EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

EntityManager em = emf.createEntityManager();
em.getTransaction().begin();

Query query = em.createQuery("Select s.s_name from StudentEntity s");
@SuppressWarnings("unchecked")
   List<String> list = query.getResultList();
   System.out.println("Student Name :");
   for (String s : list) {

System.out.println(s);

}

2.JPQL静态查询示例

使用createNamedQuery()方法从数据库中获取单个列的值。

第一步：创建StudentEntity.java，加上静态查询@NamedQuery

import javax.persistence.*;

@Entity
@Table(name = "student")
@NamedQuery(name = "find name", query = "Select s from StudentEntity s")
public class StudentEntity {

   @Id
   private int s_id;
   private String s_name;
   private int s_age;
   }

第二步：执行（这里是默认已经配置了外部元数据）

EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

EntityManager em = emf.createEntityManager();
em.getTransaction().begin();

Query query = em.createNamedQuery("find name");
@SuppressWarnings("unchecked")
   List<StudentEntity> list = query.getResultList();
   System.out.println("Student Name :");
   for (StudentEntity s : list) {

System.out.println(s.getS_name());

}

em.close();
emf.close();

3.JPQL批量查詢

第一步：创建一个名为StudentEntity.java的实体类

第二步：创建xml文件

第三步：执行

EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

EntityManager em = emf.createEntityManager();
em.getTransaction().begin();

Query query = em.createQuery("Select s from StudentEntity s ");

@SuppressWarnings("unchecked")
List<StudentEntity> list = (List<StudentEntity>) query.getResultList();

System.out.print("s_id");
System.out.print("\t s_name");
System.out.println("\t s_age");

for (StudentEntity s : list) {
   System.out.print(s.getS_id());
   System.out.print("\t" + s.getS_name());
   System.out.print("\t" + s.getS_age());
   System.out.println();
   }
em.getTransaction().commit();
em.close();
emf.close();

4.JPQL更新记录

EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

EntityManager em = emf.createEntityManager();
em.getTransaction().begin();

Query query = em.createQuery("update StudentEntity SET s_age=25 where s_id>103");
query.executeUpdate();

   em.getTransaction().commit();
   em.close();
   emf.close();

5.JPQL删除记录

EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

EntityManager em = emf.createEntityManager();
em.getTransaction().begin();

Query query = em.createQuery("delete from StudentEntity where s_id=102");

query.executeUpdate();

    em.getTransaction().commit();
    em.close();
    emf.close();

6.JPQL高级查询

EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

EntityManager em = emf.createEntityManager();
em.getTransaction().begin();

Query q1 = em.createQuery("Select s from StudentEntity s where s.s_age between 22 and 28");

@SuppressWarnings("unchecked")
List<StudentEntity> l1 = (List<StudentEntity>) q1.getResultList();

    System.out.println("Between Clause");
    System.out.print("s_id");
    System.out.print("\t s_name");
    System.out.println("\t s_age");

    for (StudentEntity s : l1) {
        System.out.print(s.getS_id());
        System.out.print("\t" + s.getS_name());
        System.out.println("\t" + s.getS_age());
    }

Query q2 = em.createQuery("Select s from StudentEntity s where s.s_age IN(20,22,23)");

@SuppressWarnings("unchecked")
List<StudentEntity> l2 = (List<StudentEntity>) q2.getResultList();

    System.out.println("IN Clause");
    System.out.print("s_id");
    System.out.print("\t s_name");
    System.out.println("\t s_age");

    for (StudentEntity s : l2) {
        System.out.print(s.getS_id());
        System.out.print("\t" + s.getS_name());
        System.out.println("\t" + s.getS_age());
    }

Query q3 = em.createQuery("Select s from StudentEntity s where s.s_name like '%a%'");

@SuppressWarnings("unchecked")
List<StudentEntity> l3 = (List<StudentEntity>) q3.getResultList();

    System.out.println("Like Clause");
    System.out.print("s_id");
    System.out.print("\t s_name");
    System.out.println("\t s_age");

    for (StudentEntity s : l3) {
        System.out.print(s.getS_id());
        System.out.print("\t" + s.getS_name());
        System.out.println("\t" + s.getS_age());
    }

    em.getTransaction().commit();
    em.close();
    emf.close();

7.JPQL聚合

EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

EntityManager em = emf.createEntityManager();
em.getTransaction().begin();

Query q1 = em.createQuery("Select count(s) from StudentEntity s");
System.out.println("Number of Student : " + q1.getSingleResult());

Query q2 = em.createQuery("Select MAX(s.s_age) from StudentEntity s");
System.out.println("Maximum age : " + q2.getSingleResult());

    Query q3 = em.createQuery("Select MIN(s.s_age) from StudentEntity s");
    System.out.println("Minimum age : " + q3.getSingleResult());
    em.getTransaction().commit();
    em.close();
    emf.close();

8.JPQL排序

EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");

EntityManager em = emf.createEntityManager();
em.getTransaction().begin();

Query q1 = em.createQuery("Select s from StudentEntity s order by s.s_age desc");

@SuppressWarnings("unchecked")
List<StudentEntity> l1 = (List<StudentEntity>) q1.getResultList();

    System.out.print("s_id");
    System.out.print("\t s_name");
    System.out.println("\t s_age");

    for (StudentEntity s : l1) {
        System.out.print(s.getS_id());
        System.out.print("\t" + s.getS_name());
        System.out.println("\t" + s.getS_age());
    }

    em.getTransaction().commit();
    em.close();
    emf.close();

学习来源：https://www.yiibai.com/jpa/jpa-jpql-bulk-data-operations.html#article-start

posted @ 2020-09-09 16:16 小窝蜗阅读(307) 评论(0) 收藏举报

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JPA(Java Persistence API)学习十六（JPQL基本操作）

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