【JPA更新实体】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。
本示例包含以下步骤：-
- 在com.srcmini.jpa.student包下创建一个名为StudentEntity.java的实体类, 该实体类包含属性s_id, s_name和s_age。
package com.srcmini.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, 在Persistence.xml文件中映射实体类和其他数据库配置。
<
persistence>
<
persistence-unit name="Student_details">
<
class>
com.srcmini.jpa.student.StudentEntity<
/class>
<
properties>
<
property name="javax.persistence.jdbc.driver" value="http://www.srcmini.com/com.mysql.jdbc.Driver"/>
<
property name="javax.persistence.jdbc.url" value="http://www.srcmini.com/jdbc:mysql://localhost:3306/studentdata"/>
<
property name="javax.persistence.jdbc.user" value="http://www.srcmini.com/root"/>
<
property name="javax.persistence.jdbc.password" value=""/>
<
property name="eclipselink.logging.level" value="http://www.srcmini.com/SEVERE"/>
<
property name="eclipselink.ddl-generation" value="http://www.srcmini.com/create-or-extend-tables"/>
<
/properties>
<
/persistence-unit>
<
/persistence>
- 在com.srcmini.jpa.update包下创建一个名为UpdateStudent.java的持久性类, 以将实体对象与数据持久化。
package com.srcmini.jpa.update;
import javax.persistence.*;
import com.srcmini.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：
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