JPA级联删除 JPA级联删除|JPA

级联删除用于指定如果删除父实体, 那么其所有相关实体也将被删除。以下语法用于执行级联删除操作：-

@OneToOne(cascade=CascadeType.REMOVE)

级联删除示例在此示例中, 我们将创建两个相互关联的实体类, 但是要建立它们之间的依赖关系, 我们将执行级联操作。
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s_id, s_name, s_age属性和标有级联规范的Subject类型的对象。

StudentEntity.java

package com.srcmini.jpa.student; import javax.persistence.*; import com.srcmini.jpa.subject.Subject; @Entity@Table(name="student")public class StudentEntity { @Id private int s_id; private String s_name; private int s_age; @OneToOne(cascade={CascadeType.REMOVE}) private Subject sub; public Subject getSub() {return sub; } public void setSub(Subject sub) {this.sub = sub; } public StudentEntity(int s_id, String s_name, int s_age , Subject sub) {super(); this.s_id = s_id; this.s_name = s_name; this.s_age = s_age; this.sub=sub; } 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; } }

在com.srcmini.jpa.subject包下创建另一个名为Subject.java的实体类。

Subject.java

package com.srcmini.jpa.subject; import javax.persistence.*; @Entity@Table(name="subject")public class Subject { private String name; private int marks; @Id private int s_id; public Subject(String name, int marks, int s_id) {super(); this.name = name; this.marks = marks; this.s_id=s_id; } public Subject() {super(); } public String getName() {return name; } public void setName(String name) {this.name = name; } public int getMarks() {return marks; } public void setMarks(int marks) {this.marks = marks; } public int getS_id() {return s_id; } public void setS_id(int s_id) {this.s_id = s_id; } }

现在, 在Persistence.xml文件中映射实体类和其他数据库配置。

Persistence.xml

< persistence> < persistence-unit name="Student_details"> < class> com.srcmini.jpa.student.StudentEntity< /class> < class> com.srcmini.jpa.subject.Subject< /class> < properties> < 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="javax.persistence.jdbc.driver" value="http://www.srcmini.com/com.mysql.jdbc.Driver"/> < 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.cascade包下创建一个名为StudentCascade.java的持久性类, 以将实体对象与数据持久化。

【JPA级联删除】StudentCascade.java

package com.srcmini.jpa.cascade; import javax.persistence.*; import com.srcmini.jpa.student.*; public class StudentCascade {public static void main( String[ ] args ) {EntityManagerFactory emf = Persistence.createEntityManagerFactory( "Student_details" ); EntityManager em = emf.createEntityManager( ); em.getTransaction().begin(); StudentEntity s=em.find(StudentEntity.class, 101); em.remove(s); em.getTransaction().commit(); em.close( ); emf.close( ); } }

输出：
程序执行后, 将在MySQL工作台下生成以下表格。