hibernate cascade=CascadeType.All

 因为时间关系，我在这里测试的环境是一对多的关系里面用到的注解方式的级联，网上也有很多贴子，我也看过了，但是呢，我还是自己总结一下吧，这觉得级联是单向的，不是双向的，意思就是说，我们在设置两个类的对象之间关系的时候，总是在一方设置的很具体，在另外一方设置一个mappedBy即可，但是如果想要两边都能删除的时候，或者在生成的时候，必须在两边都设置cascade=CascadeType.All才有效果，下面是测试代码，测试样例是参考马士兵的视频做的，

package com.jll.model;



import java.util.HashSet;

import java.util.Set;



import javax.persistence.CascadeType;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.OneToMany;

import javax.persistence.Table;



@Entity

@Table(name="t_group")

public class Group {

    private int id;

    private String name;

    private Set<User> users = new HashSet<User>();



    @Id

    @GeneratedValue

    public int getId() {

        return id;

    }



    public String getName() {

        return name;

    }



    @OneToMany(mappedBy="group",cascade=CascadeType.ALL)

    public Set<User> getUsers() {

        return users;

    }



    public void setId(int id) {

        this.id = id;

    }



    public void setName(String name) {

        this.name = name;

    }



    public void setUsers(Set<User> users) {

        this.users = users;

    }



}

现在这里有cascade=CascadeType.ALL。在相关联的类的另一边同样也有，

package com.jll.model;



import javax.persistence.CascadeType;

import javax.persistence.Entity;

import javax.persistence.GeneratedValue;

import javax.persistence.Id;

import javax.persistence.JoinColumn;

import javax.persistence.ManyToOne;

import javax.persistence.Table;



@Entity

@Table(name = "t_user")

public class User {

    private int id;

    private String name;

    private Group group;



    @ManyToOne(cascade=CascadeType.ALL)

    @JoinColumn(name="groupId")

    public Group getGroup() {

        return group;

    }



    @Id

    @GeneratedValue

    public int getId() {

        return id;

    }



    public String getName() {

        return name;

    }



    public void setGroup(Group group) {

        this.group = group;

    }



    public void setId(int id) {

        this.id = id;

    }



    public void setName(String name) {

        this.name = name;

    }

    

    public String toString(){

        return this.getName()+"---"+this.getId()+"---"+this.getGroup().getId();

    }



}

测试代码：

package com.jll.model;



import java.util.HashSet;

import java.util.Iterator;

import java.util.Set;



import org.hibernate.Session;

import org.hibernate.SessionFactory;

import org.hibernate.boot.registry.StandardServiceRegistryBuilder;

import org.hibernate.cfg.Configuration;

import org.hibernate.tool.hbm2ddl.SchemaExport;

import org.junit.AfterClass;

import org.junit.BeforeClass;

import org.junit.Ignore;

import org.junit.Test;



public class TestCoreAPI {

    

    private static SessionFactory sf=null;

    private static Configuration configuration = new Configuration().configure();

    

    @BeforeClass

    public static void beforeClass(){

        StandardServiceRegistryBuilder builder = new StandardServiceRegistryBuilder().

        applySettings(configuration.getProperties());

        sf = configuration.buildSessionFactory(builder.build());

    }

    

    @AfterClass

    public static void afterClass(){

        sf.close();

    }

@Test

    public void testRelationShip(){

        SchemaExport se = new SchemaExport(configuration);

        se.create(true, true);

        Session session  = sf.getCurrentSession();

        Group g = new Group();

        g.setName("group1");

        User u1 = new User();

        User u2 = new User();

        /*u1.setGroup(g);

        u2.setGroup(g);*/

        u1.setName("u1");

        u2.setName("u2");

        Set<User> users = new HashSet<User>();

        users.add(u1);

        users.add(u2);

        g.setUsers(users);

        session.beginTransaction();

        session.save(g);

        session.getTransaction().commit();

    }

生成的SQL语句如下：

alter table t_user 

        drop 

        foreign key FK_7ktm6l2qkykpqrf6oq01ys8wy



    drop table if exists t_group



    drop table if exists t_user



    create table t_group (

        id integer not null auto_increment,

        name varchar(255),

        primary key (id)

    )



    create table t_user (

        id integer not null auto_increment,

        name varchar(255),

        groupId integer,

        primary key (id)

    )



    alter table t_user 

        add constraint FK_7ktm6l2qkykpqrf6oq01ys8wy 

        foreign key (groupId) 

        references t_group (id)

Hibernate: 

    insert 

    into

        t_group

        (name) 

    values

        (?)

Hibernate: 

    insert 

    into

        t_user

        (groupId, name) 

    values

        (?, ?)

Hibernate: 

    insert 

    into

        t_user

        (groupId, name) 

    values

        (?, ?)

如果Group类没有加上级联的话，生成的语句如下：

alter table t_user 

        drop 

        foreign key FK_7ktm6l2qkykpqrf6oq01ys8wy



    drop table if exists t_group



    drop table if exists t_user



    create table t_group (

        id integer not null auto_increment,

        name varchar(255),

        primary key (id)

    )



    create table t_user (

        id integer not null auto_increment,

        name varchar(255),

        groupId integer,

        primary key (id)

    )



    alter table t_user 

        add constraint FK_7ktm6l2qkykpqrf6oq01ys8wy 

        foreign key (groupId) 

        references t_group (id)

Hibernate: 

    insert 

    into

        t_group

        (name) 

    values

        (?)

这里只插入了一次，而上面的那个插入了三次，所以我猜测级联是单向的，不是双向的，如果想要两边都可以进行crud，则被关联的类都要加上cascade=CascadeType.ALL,我也进行了删除测试，删除的时候必须先查出来，然后才能进行级联删除，得出来的结论也是与上面的实验一样，在这里就不贴代码了。