在上一节中，我们只提取了单列的值。 现在，我们将学习如何处理批量数据并执行相应的操作。

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批量数据示例

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.zyiz.jpa包下创建一个名为StudentEntity.java的实体类。

文件:StudentEntity.java -

package com.zyiz.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.zyiz.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>

在 StudentEntity.java 类上执行以下操作。

1. JPQL提取记录

在这里，我们将从数据库中提取所有记录。

文件:FetchData.java -

package com.zyiz.jpa.jpql;

import com.zyiz.jpa.StudentEntity;
import javax.persistence.*;
import java.util.*;

public class FetchData {

    public static void main(String args[]) {

        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();
    }
}

执行上面示例代码，得到以下结果 -

s_id     s_name     s_age
   Gaurav    24
   Rahul    22
   Chris    20
   Ronit    26
   Roy    21

2. JPQL更新记录

在这里，我们将更新数据库中的记录。

文件:UpdateData.java -

package com.zyiz.jpa.jpql;

import javax.persistence.*;

public class UpdataData {

    public static void main(String args[]) {

        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();
    }
}

执行上面示例代码后，在MySQL工作台下生成以下student表。 要查看数据，请在MySQL中运行select * from student。

mysql> select * from student;
+------+--------+-------+
| S_ID | S_NAME | S_AGE |
+------+--------+-------+
|  101 | Gaurav |    24 |
|  102 | Rahul  |    22 |
|  103 | Chris  |    20 |
|  104 | Ronit  |    25 |
|  105 | Roy    |    25 |
+------+--------+-------+
rows in set

3. JPQL删除记录

在这里，我们将从数据库中删除特定的记录。

文件:DeleteData.java -

package com.zyiz.jpa.jpql;

import javax.persistence.*;

public class DeleteData {

    public static void main(String args[]) {

        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();
    }
}

执行上面示例代码后，在MySQL工作台下生成以下student表。 要查看数据，请在MySQL中运行select * from student。如下结果 -

mysql> select * from student;
+------+--------+-------+
| S_ID | S_NAME | S_AGE |
+------+--------+-------+
|  101 | Gaurav |    24 |
|  103 | Chris  |    20 |
|  104 | Ronit  |    25 |
|  105 | Roy    |    25 |
+------+--------+-------+
rows in set