JPA允许我们通过更新实体来更改数据库中的记录。

JPA实体更新示例

在这里，我们将演示如何根据主键更新学生的年龄。

完整的项目代码如下所示 -

这个例子包含以下步骤 -

第1步: 在com.zyiz.jpa.student包下创建一个名为StudentEntity.java的实体类，它包含属性:s_id，s_name和s_age。

文件:StudentEntity.java 的代码如下 -

package com.zyiz.jpa.student;

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;
    }

}

第2步: 将实体类和其他数据库配置映射到persistence.xml文件中。

文件:persistence.xml 的代码如下 -

<?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.student.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com.zyiz.jpa.student包下创建一个名为UpdateStudent.java的持久化类，以便将实体对象与数据保持一致。

文件:UpdateStudent.java 的代码如下 -

package com.zyiz.jpa.student;

import javax.persistence.*;

import com.zyiz.jpa.student.*;

public class UpdateStudent {

    public static void main(String args[]) {
        EntityManagerFactory emf = Persistence.createEntityManagerFactory("Student_details");
        EntityManager em = emf.createEntityManager();

        StudentEntity s = em.find(StudentEntity.class, 1001);
        System.out.println("Before Updation");
        System.out.println("Student id = " + s.getS_id());
        System.out.println("Student Name = " + s.getS_name());
        System.out.println("Student Age = " + s.getS_age());

        s.setS_age(30);

        System.out.println("After Updation");
        System.out.println("Student id = " + s.getS_id());
        System.out.println("Student Name = " + s.getS_name());
        System.out.println("Student Age = " + s.getS_age());

    }

}

执行上面示例代码，得到以下结果 -

Before Updation
Student id = 1001
Student Name = Maxsu
Student Age = 26
After Updation
Student id = 1001
Student Name = Maxsu
Student Age = 30