Mybatis一对一和一对多配置

作者：夕下奕林

• 问题描述

现在有三张数据表，表名为orders,orderdetail,items，分别表示订单，订单详情，商品。

其中一个订单包含多个订单详情，表示订单中的不同个具体的商品，订单详情唯一对应一件商品。所以orderdetail中的外键order_id为orders的主键，orderdetail中的外键items_id为items的主键。

• 数据库结构

  DROP TABLE IF EXISTS `items`;
  /*!40101 SET @saved_cs_client     = @@character_set_client */;
  /*!40101 SET character_set_client = utf8 */;
  CREATE TABLE `items` (
    `id` int(11) NOT NULL auto_increment,
    `name` varchar(32) NOT NULL COMMENT '商品名称',
    `price` float(10,1) NOT NULL COMMENT '商品定价',
    `detail` text COMMENT '商品描述',
    `pic` varchar(64) default NULL COMMENT '商品图片',
    `createtime` datetime NOT NULL COMMENT '生产日期',
    PRIMARY KEY  (`id`)
  ) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;
  /*!40101 SET character_set_client = @saved_cs_client */;
  
  --
  -- Table structure for table `orderdetail`
  --
  
  DROP TABLE IF EXISTS `orderdetail`;
  /*!40101 SET @saved_cs_client     = @@character_set_client */;
  /*!40101 SET character_set_client = utf8 */;
  CREATE TABLE `orderdetail` (
    `id` int(11) NOT NULL auto_increment,
    `orders_id` int(11) NOT NULL COMMENT '订单id',
    `items_id` int(11) NOT NULL COMMENT '商品id',
    `items_num` int(11) default NULL COMMENT '商品购买数量',
    PRIMARY KEY  (`id`),
    KEY `FK_orderdetail_1` (`orders_id`),
    KEY `FK_orderdetail_2` (`items_id`),
    CONSTRAINT `FK_orderdetail_1` FOREIGN KEY (`orders_id`) REFERENCES `orders` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION,
    CONSTRAINT `FK_orderdetail_2` FOREIGN KEY (`items_id`) REFERENCES `items` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION
  ) ENGINE=InnoDB AUTO_INCREMENT=5 DEFAULT CHARSET=utf8;
  /*!40101 SET character_set_client = @saved_cs_client */;
  
  --
  -- Table structure for table `orders`
  --
  
  DROP TABLE IF EXISTS `orders`;
  /*!40101 SET @saved_cs_client     = @@character_set_client */;
  /*!40101 SET character_set_client = utf8 */;
  CREATE TABLE `orders` (
    `id` int(11) NOT NULL auto_increment,
    `user_id` int(11) NOT NULL COMMENT '下单用户id',
    `number` varchar(32) NOT NULL COMMENT '订单号',
    `createtime` datetime NOT NULL COMMENT '创建订单时间',
    `note` varchar(100) default NULL COMMENT '备注',
    PRIMARY KEY  (`id`),
    KEY `FK_orders_1` (`user_id`),
    CONSTRAINT `FK_orders_id` FOREIGN KEY (`user_id`) REFERENCES `user` (`id`) ON DELETE NO ACTION ON UPDATE NO ACTION
  ) ENGINE=InnoDB AUTO_INCREMENT=6 DEFAULT CHARSET=utf8;

根据表创建pojo类：

Items.Java

package cn.elinzhou.mybatisTest.pojo;

import java.util.Date;

/**
 * Description: Items
 * Author: Elin Zhou
 * Create: 2015-06-30 00:57
 */
public class Items {
    private Integer id;
    private String name;
    private Double price;
    private String detail;
    private String pic;
    private Date createtime;

    public Date getCreatetime() {
        return createtime;
    }

    public void setCreatetime(Date createtime) {
        this.createtime = createtime;
    }

    public String getDetail() {
        return detail;
    }

    public void setDetail(String detail) {
        this.detail = detail;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getPic() {
        return pic;
    }

    public void setPic(String pic) {
        this.pic = pic;
    }

    public Double getPrice() {
        return price;
    }

    public void setPrice(Double price) {
        this.price = price;
    }

    @Override
    public String toString() {
        return "Items{" +
                "createtime=" + createtime +
                ", id=" + id +
                ", name='" + name + '\'' +
                ", price=" + price +
                ", detail='" + detail + '\'' +
                ", pic='" + pic + '\'' +
                '}';
    }
}

Order.java

package cn.elinzhou.mybatisTest.pojo;

import java.util.Date;

/**
 * Description: Orders
 * Author: Elin Zhou
 * Create: 2015-06-30 00:06
 */
public class Orders {
//    id | user_id | number  | createtime          | note |
    private Integer id;
    private Integer user_id;
    private String number;
    private Date createtime;
    private String note;

    public Date getCreatetime() {
        return createtime;
    }

    public void setCreatetime(Date createtime) {
        this.createtime = createtime;
    }

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getNote() {
        return note;
    }

    public void setNote(String note) {
        this.note = note;
    }

    public String getNumber() {
        return number;
    }

    public void setNumber(String number) {
        this.number = number;
    }

    public Integer getUser_id() {
        return user_id;
    }

    public void setUser_id(Integer user_id) {
        this.user_id = user_id;
    }

    @Override
    public String toString() {
        return "Orders{" +
                "createtime=" + createtime +
                ", id=" + id +
                ", user_id=" + user_id +
                ", number='" + number + '\'' +
                ", note='" + note + '\'' +
                '}';
    }
}

OrderDetail.java

package cn.elinzhou.mybatisTest.pojo;

/**
 * Description: OrderDetail
 * Author: Elin Zhou
 * Create: 2015-06-30 00:08
 */
public class OrderDetail {
//    id | orders_id | items_id | items_num
    private Integer id;
    private Integer orders_id;
    private Integer items_id;
    private Integer items_num;
    public Integer getId() {

        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Integer getItems_id() {
        return items_id;
    }

    public void setItems_id(Integer items_id) {
        this.items_id = items_id;
    }

    public Integer getItems_num() {
        return items_num;
    }

    public void setItems_num(Integer items_num) {
        this.items_num = items_num;
    }

    public Integer getOrders_id() {
        return orders_id;
    }

    public void setOrders_id(Integer orders_id) {
        this.orders_id = orders_id;
    }

    @Override
    public String toString() {
        return "OrderDetail{" +
                "id=" + id +
                ", orders_id=" + orders_id +
                ", items_id=" + items_id +
                ", items_num=" + items_num +
                '}';
    }
}

POJO由于对应这数据库字段，所以不方便修改，为了方便拓展，添加两个类OrderCustom和OrderDetailCustom，用来包含所需要的POJO对象

OrderCustom.java

package cn.elinzhou.mybatisTest.pojo;

/**
 * Description: OrderDetailCustom
 * Author: Elin Zhou
 * Create: 2015-06-30 00:56
 */
public class OrderDetailCustom extends OrderDetail {
    private Items items;

    public Items getItems() {
        return items;
    }

    public void setItems(Items items) {
        this.items = items;
    }

    @Override
    public String toString() {
        return "OrderDetailCustom{" +
                "items=" + items +
                '}';
    }
}

OrderDetailCustom.java

package cn.elinzhou.mybatisTest.pojo;

import java.util.List;

/**
 * Description: OrdersCustrom
 * Author: Elin Zhou
 * Create: 2015-06-30 00:35
 */
public class OrdersCustrom extends Orders {
    private List<OrderDetailCustom> orderDetails;

    public List<OrderDetailCustom> getOrderDetails() {
        return orderDetails;
    }

    public void setOrderDetails(List<OrderDetailCustom> orderDetails) {
        this.orderDetails = orderDetails;
    }

    @Override
    public String toString() {
        return "OrdersCustrom{" +
                "orderDetails=" + orderDetails +
                '}';
    }
}

OrderCustom继承自Order，添加了一个List 
OrderDetailCustom继承自OrderDetail,添加了一个Items

• Mapper接口

本案例只实现订单的获取功能，所以在OrderMapper中只定义个findOrders方法

OrderMapper.java

package cn.elinzhou.mybatisTest.mapper;

import cn.elinzhou.mybatisTest.pojo.OrdersCustrom;

import java.util.List;

/**
 * Description: OrdersMapper
 * Author: Elin Zhou
 * Create: 2015-06-30 00:32
 */
public interface OrdersMapper {
    List<OrdersCustrom> findOrders() throws Exception;
}

• OrderMapper.xml

这里需要用到两个标签，< collection >和< association >

< collection >用来表示一对多关系，如订单包含多个订单详情就可以用这个标签，主要用到两个属性： 
property：属性名，可以理解为在该类型在父类型中的属性名 
ofType：该属性所对应的POJO类型

<collection property="orderDetails" ofType="cn.elinzhou.mybatisTest.pojo.OrderDetailCustom">

< association >用来表示一对一关系，如订单详情对应一件商品，主要用到两个属性 
property：属性名，可以理解为在该类型在父类型中的属性名 
javaType：该属性所对应的POJO类型

特别注意，collection和association中描述POJO类型的属性名是不同的，collection是ofType，association是javaType

sql

为了方便重用，定了了三个sql标签，用来表示从三张表中索要查找的字段

<!--orders字段-->
<sql id="orders_column_tablename">
    orders.id orders_id,orders.user_id orders_user_id,
    orders.number orders_number,orders.createtime orders_createtime,orders.note orders_note
</sql>
<!--orderdetail字段-->
<sql id="orderdetail_column_tablename">
    orderdetail.id orderdetail_id,orderdetail.orders_id orderdetail_orders_id,
    orderdetail.items_id orderdetail_items_id,orderdetail.items_num orderdetail_items_num
</sql>
<!--items字段-->
<sql id="items_column_tablename">
    items.id items_id,items.name items_name,items.price items_price,
    items.detail items_detail,items.pic items_pic,items.createtime items_createtime
</sql>

select标签

<select id="findOrders" resultMap="OrderResultMap">
    SELECT
    <include refid="orders_column_tablename"/>,
    <include refid="orderdetail_column_tablename"/>,
    <include refid="items_column_tablename"/>
    FROM
    orders INNER JOIN orderdetail ON orders.id = orderdetail.orders_id
    INNER JOIN items ON orderdetail.items_id = items.id
</select>

OrderResultMap就要勇当之前说过的collection和association标签，其余的部分与普通的resultMap的方式一样

<resultMap id="OrderResultMap" type="cn.elinzhou.mybatisTest.pojo.OrdersCustrom">
    <id column="orders_id" property="id"/>
    <result column="orders_user_id" property="user_id"/>
    <result column="orders_number" property="number"/>
    <result column="orders_createtime" property="createtime"/>
    <result column="orders_note" property="note"/>

    <!--订单详情list-->
    <collection property="orderDetails" ofType="cn.elinzhou.mybatisTest.pojo.OrderDetailCustom">
        <id column="orderdetail_id" property="id"/>
        <result column="orderdetail_orders_id" property="orders_id"/>
        <result column="orderdetail_items_id" property="items_id"/>
        <result column="orderdetail_items_num" property="items_num"/>

        <!--商品信息-->
        <association property="items" javaType="cn.elinzhou.mybatisTest.pojo.Items">
            <id column="items_id" property="id"/>
            <result column="items_name" property="name"/>
            <result column="items_price" property="price"/>
            <result column="items_detail" property="detail"/>
            <result column="items_pic" property="pic"/>
            <result column="items_createtime" property="createtime"/>
        </association>
    </collection>
</resultMap>

POJO之间的关系，也相当于数据表之间的关系，只要定义好了主键和外键，mybatis会自动进行关联。如果没有定义外键需要在collection或者associatio中指明column_id

• 测试代码

  package cn.elinzhou.mybatisTest.test;
  
  import cn.elinzhou.mybatisTest.mapper.OrdersMapper;
  import cn.elinzhou.mybatisTest.pojo.Orders;
  import cn.elinzhou.mybatisTest.pojo.OrdersCustrom;
  import org.apache.ibatis.io.Resources;
  import org.apache.ibatis.session.SqlSession;
  import org.apache.ibatis.session.SqlSessionFactory;
  import org.apache.ibatis.session.SqlSessionFactoryBuilder;
  import org.junit.Before;
  import org.junit.Test;
  
  import java.io.Reader;
  import java.util.List;
  
  /**
   * Created by elin on 15-6-30.
   */
  public class OrderMapperTest {
  
      SqlSession sqlSession = null;
  
      @Before
      public void setUp() throws Exception {
          // 通过配置文件获取数据库连接信息
          Reader reader = Resources.getResourceAsReader("cn/elinzhou/mybatisTest/config/mybatis.xml");
          // 通过配置信息构建一个SqlSessionFactory
                  SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
          // 通过sqlSessionFactory打开一个数据库会话
          sqlSession = sqlSessionFactory.openSession();
      }
  
      @Test
      public void testFindOrders() throws Exception {
          OrdersMapper orderMapper = sqlSession.getMapper(OrdersMapper.class);
          List<OrdersCustrom> list = orderMapper.findOrders();
  
          System.out.println(list);
      }
  }