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hibernate入门使用系列 7-- annotation关系映射篇(中)

这次说说OneToMany和ManyToOne

我们的场景是 1个父亲n多个孩子

先来看看这中做法:

TestFather.java

package net.paoding.forum.domain;

import java.util.ArrayList;
import java.util.List;

import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.OneToMany;

@Entity
public class TestFather
{
    String          id;
    String          name;
    List children = new ArrayList();

    /**
     * @return the id
     */
    @Id
    public String getId()
    {
        return id;
    }

    /**
     * @param id the id to set
     */
    public void setId(String id)
    {
        this.id = id;
    }

    /**
     * @return the name
     */
    public String getName()
    {
        return name;
    }

    /**
     * @param name the name to set
     */
    public void setName(String name)
    {
        this.name = name;
    }

    /**
     * @return the children
     */
    @OneToMany
    public List getChildren()
    {
        return children;
    }

    /**
     * @param children the children to set
     */
    public void setChildren(List children)
    {
        this.children = children;
    }
}

TestChild.java

package net.paoding.forum.domain;

import javax.persistence.Entity;
import javax.persistence.Id;

@Entity
public class TestChild
{
    String     id;
    String     name;

    /**
     * @return the id
     */
    @Id
    public String getId()
    {
        return id;
    }

    /**
     * @param id the id to set
     */
    public void setId(String id)
    {
        this.id = id;
    }

    /**
     * @return the name
     */
    public String getName()
    {
        return name;
    }

    /**
     * @param name the name to set
     */
    public void setName(String name)
    {
        this.name = name;
    }
}

这样子,好像就可以了。那么是的么?我们来看看hib产生的sql

drop table test_child cascade constraints;
drop table test_father cascade constraints;
drop table test_father_children cascade constraints;

create table test_child (
    id varchar2(255 char) not null,
    name varchar2(255 char),
    primary key (id)
);

create table test_father (
    id varchar2(255 char) not null,
    name varchar2(255 char),
    primary key (id)
);

create table test_father_children (
    null_id varchar2(255 char) not null,
    children_id varchar2(255 char) not null,
    unique (children_id)
);


alter table test_father_children 
    add constraint FK2E6E87D5901B7DBB 
    foreign key (null_id) 
    references test_father;

alter table test_father_children 
    add constraint FK2E6E87D58CD0E56B 
    foreign key (children_id) 
    references test_child;

alter table test_user 
    add constraint FKB9A96B58A237D846 
    foreign key (card_id) 
    references test_card;

oh! My God !它居然又帮我们多创建了一个table。作为关联。太笨了。

很明显,这不是我们所需要的。

那我们该如何呢?见下篇