使用JPQL，我们可以执行任何类型的数据库操作。 在这里，我们将使用简单的例子来执行JPQL的一些高级操作。
假设当前student表有如下数据 -
DROP TABLE IF EXISTS `student`; CREATE TABLE `student` ( `S_ID` int(11) NOT NULL, `S_NAME` varchar(255) DEFAULT NULL, `S_AGE` int(11) DEFAULT NULL, PRIMARY KEY (`S_ID`) ) ENGINE=MyISAM DEFAULT CHARSET=utf8; -- ---------------------------- -- Records of student -- ---------------------------- INSERT INTO `student` VALUES ('101', 'Gaurav', '24'); INSERT INTO `student` VALUES ('102', 'Rahul', '22'); INSERT INTO `student` VALUES ('103', 'Chris', '20'); INSERT INTO `student` VALUES ('104', 'Ronit', '26'); INSERT INTO `student` VALUES ('105', 'Roy', '21'); JPQL高级查询示例
在这个例子中，我们将采用一个基本的实体类(StudentEntity.java)并对其执行不同的操作。
在com.yiibai.jpa包下创建一个名为StudentEntity.java的实体类。
文件:StudentEntity.java -
package com.yiibai.jpa;
import javax.persistence.*; @Entity @Table(name = "student") public class StudentEntity { @Id private int s_id; private String s_name; private int s_age; public StudentEntity(int s_id, String s_name, int s_age) { super(); this.s_id = s_id; this.s_name = s_name; this.s_age = s_age; } public StudentEntity() { super(); } public int getS_id() { return s_id; } public void setS_id(int s_id) { this.s_id = s_id; } public String getS_name() { return s_name; } public void setS_name(String s_name) { this.s_name = s_name; } public int getS_age() { return s_age; } public void setS_age(int s_age) { this.s_age = s_age; } } 现在，将实体类和其他数据库配置映射到Persistence.xml文件中。
文件:persistence.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> 现在，我们可以在StudentEntity.java类中执行以下操作。
1. JPQL筛选器
在这里，我们将在student表上执行一些过滤操作。
文件:Filter.java -
package com.yiibai.jpa.jpql; import com.yiibai.jpa.StudentEntity; import javax.persistence.*; import java.util.*; public class Filter { public static void main(String args[]) { 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"