Mybatis一對一和一對多配置

• 問題描述

如今有三張數據表，表名爲orders,orderdetail,items，分別表示訂單，訂單詳情，商品。

其中一個訂單包含多個訂單詳情，表示訂單中的不一樣個具體的商品，訂單詳情惟一對應一件商品。因此orderdetail中的外鍵order_id爲orders的主鍵，orderdetail中的外鍵items_id爲items的主鍵。

• 數據庫結構

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 '商品名稱', `price` float(10,1) NOT NULL COMMENT '商品訂價', `detail` text COMMENT '商品描述', `pic` varchar(64) default NULL COMMENT '商品圖片', `createtime` datetime NOT NULL COMMENT '生產日期', 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 '訂單id', `items_id` int(11) NOT NULL COMMENT '商品id', `items_num` int(11) default NULL COMMENT '商品購買數量', 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 '下單用戶id', `number` varchar(32) NOT NULL COMMENT '訂單號', `createtime` datetime NOT NULL COMMENT '建立訂單時間', `note` varchar(100) default NULL COMMENT '備註', 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;

• POJO

根據表建立pojo類：

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因爲對應這數據庫字段，因此不方便修改，爲了方便拓展，添加兩個類OrderCustom和OrderDetailCustom，用來包含所須要的POJO對象

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繼承自Order，添加了一個List
OrderDetailCustom繼承自OrderDetail,添加了一個Items

• Mapper接口

本案例只實現訂單的獲取功能，因此在OrderMapper中只定義個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

這裏須要用到兩個標籤，< collection >和< association >

< collection >用來表示一對多關係，如訂單包含多個訂單詳情就能夠用這個標籤，主要用到兩個屬性：
property：屬性名，能夠理解爲在該類型在父類型中的屬性名
ofType：該屬性所對應的POJO類型

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

< association >用來表示一對一關係，如訂單詳情對應一件商品，主要用到兩個屬性
property：屬性名，能夠理解爲在該類型在父類型中的屬性名
javaType：該屬性所對應的POJO類型

特別注意，collection和association中描述POJO類型的屬性名是不一樣的，collection是ofType，association是javaType

sql

爲了方便重用，定了了三個sql標籤，用來表示從三張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標籤

<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就要勇當以前說過的collection和association標籤，其他的部分與普通的resultMap的方式同樣

<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"/>

    <!--訂單詳情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之間的關係，也至關於數據表之間的關係，只要定義好了主鍵和外鍵，mybatis會自動進行關聯。

• 測試代碼

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 {
        // 經過配置文件獲取數據庫鏈接信息
        Reader reader = Resources.getResourceAsReader("cn/elinzhou/mybatisTest/config/mybatis.xml");
        // 經過配置信息構建一個SqlSessionFactory
                SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(reader);
        // 經過sqlSessionFactory打開一個數據庫會話
        sqlSession = sqlSessionFactory.openSession();
    }

    @Test
    public void testFindOrders() throws Exception {
        OrdersMapper orderMapper = sqlSession.getMapper(OrdersMapper.class);
        List<OrdersCustrom> list = orderMapper.findOrders();

        System.out.println(list);
    }
}