JPA 级联删除

2024 年 8 月 29 日 | 阅读 3 分钟

级联删除用于指定如果删除父实体，则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： -

级联删除示例

在此示例中，我们将创建两个彼此相关的实体类，但为了建立它们之间的依赖关系，我们将执行级联操作。

此示例包含以下步骤： -

创建一个名为 StudentEntity.java 的实体类，该类位于 com.javatpoint.jpa.student 包下，包含属性 s_id、s_name、s_age 以及一个使用级联规范标记的 Subject 类型的对象。

StudentEntity.java

package com.javatpoint.jpa.student;
import javax.persistence.*;
import com.javatpoint.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;
	}
	
}

创建另一个名为 Subject.java 的实体类，该类位于 com.javatpoint.jpa.subject 包下。

Subject.java

package com.javatpoint.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.javatpoint.jpa.student.StudentEntity</class>
    <class>com.javatpoint.jpa.subject.Subject</class>
      <properties>
         <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="javax.persistence.jdbc.driver" value="com.mysql.jdbc.Driver"/>
         <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 StudentCascade.java 的持久化类，该类位于 com.javatpoint.jpa.cascade 包下，用于持久化具有数据的实体对象。

StudentCascade.java

package com.javatpoint.jpa.cascade;
import javax.persistence.*;
import com.javatpoint.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 workbench 下生成以下表。