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。