更新实体

2024 年 8 月 29 日 | 阅读 2 分钟

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，我们将根据主键更新学生的年龄。

此示例包含以下步骤： -

创建一个名为 StudentEntity.java 的实体类，放在 com.javatpoint.jpa.student 包下，它包含属性 s_id、s_name 和 s_age。

StudentEntity.java

package com.javatpoint.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;
	}
	
}

现在，将实体类和其他数据库配置映射到 Persistence.xml 文件中。

Persistence.xml

<persistence>
<persistence-unit name="Student_details">
	
	<class>com.javatpoint.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://:3306/studentdata"/>
<property name="javax.persistence.jdbc.user" value="root"/>
<property name="javax.persistence.jdbc.password" value=""/>
<property name="eclipselink.logging.level" value="SEVERE"/>
<property name="eclipselink.ddl-generation" value="create-or-extend-tables"/>
</properties>

	</persistence-unit>
</persistence>

创建一个名为 UpdateStudent.java 的持久化类，放在 com.javatpoint.jpa.update 包下，用于持久化带有数据的实体对象。

UpdateStudent.java

package com.javatpoint.jpa.update;
import javax.persistence.*;

import com.javatpoint.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,102);
		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());
		
		
	}

}

输出