hibernate课程 初探一对多映射2-5 创建持久化类并配置映射文件

学习点：

1　　一对多映射，一方 Grade.hbm.xml的写法：

<hibernate-mapping>
    <class name="com.ddwei.entity.Grade" table="grade">
        <id name="gid"   type="java.lang.Integer">
            <column name="GID" />
            <generator class="increment" />
        </id>
        <property name="gname" type="java.lang.String">
            <column name="GNAME" length="20" not-null="true"/>
        </property>

<!--    配置单向的一对多关系 -->
        <set name="students" table="student">
<!--         指定的外键列 -->
         <key column="gid">
         </key>
         <one-to-many class="com.ddwei.entity.Student"/>
        </set>
        </class>
</hibernate-mapping>

2    一对多映射，cfg.xml引入hbm路径方法

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE hibernate-configuration PUBLIC
        "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
        "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
<hibernate-configuration>
    <session-factory>
        <property name="connection.driver_class">com.mysql.jdbc.Driver</property>
        <property name="connection.url">jdbc:mysql://localhost:3306/bendi?useUnicode=true&CharacterEncoding=utf8</property>
        <property name="connection.username">root</property>
        <property name="connection.password">***</property>
        <property name="dialect">org.hibernate.dialect.MySQLDialect</property>

        <property name="show_sql">true</property>
        <property name="format_sql">true</property>
        <property name="hbm2ddl.auto">update</property>

        <mapping resource = "com/ddwei/entity/Grade.hbm.xml"/>
        <mapping resource = "com/ddwei/entity/Student.hbm.xml"/>
    </session-factory>
</hibernate-configuration>

3　　一对多映射，一方java类引入多方方式

package com.ddwei.entity;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.Set;

public class Grade {
    private int gid;
    private String gname;
    private String gdesc;

    //在一方定义多方的集合
    //一个班级有多个学生，且每个学生都是唯一的，所以用Set集合
    private Set<Student> student = new HashSet<Student>();

    public int getGid() {
        return gid;
    }

    public void setGid(int gid) {
        this.gid = gid;
    }

    public String getGname() {
        return gname;
    }

    public void setGname(String gname) {
        this.gname = gname;
    }

    public String getGdesc() {
        return gdesc;
    }

    public void setGdesc(String gdesc) {
        this.gdesc = gdesc;
    }

    public Set<Student> getStudent() {
        return student;
    }

    public void setStudent(Set<Student> student) {
        this.student = student;
    }

    public Grade(){
        super();
    }

    public Grade(int gid, String gname, String gdesc, Set<Student> student) {
        super();
        this.gid = gid;
        this.gname = gname;
        this.gdesc = gdesc;
        this.student = student;
    }

}