public class OrderCustom extends Orders{
   //添加用户信息
   private String username;
   private String sex;
   private String address;
   public String getUsername() {
     return username;
   }
   public void setUsername(String username) {
     this.username = username;
   }
   public String getSex() {
     return sex;
   }
   public void setSex(String sex) {
     this.sex = sex;
   }
   public String getAddress() {
     return address;
   }
   public void setAddress(String address) {
     this.address = address;
   }
 }

 <select id="findOrderUser" resultType="com.luchao.mybatis.first.po.OrderCustom">
     select
     orders.*,
     user.username,
     user.sex,
     user.address
     from orders,user
     where
     orders.user_id = user.id
 </select>

//查询订单和用户信息
 public List<OrderCustom> findOrderUser() throws Exception;

 public void findOrdersUser() throws Exception {
     // 获取sqlSession对象
     SqlSession sqlSession = sqlSessionFactory.openSession();
     // 创建OrderMapper对象，MyBatis自动生成mapper代理
     OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class);
     // 调用orderMapper的方法，查询订单和用户信息
     List<OrderCustom> orderCustoms = orderMapper.findOrderUser();
     System.out.println(orderCustoms.size());
 }

public class Orders {
   private Integer id;
   private Integer userId;
   private String number;
   private Date createtime;
   private String note;
   //用户信息
   private User user;
   //订单条目
   private List<Orderdetail> orderdetails;
   public Integer getId() {
     return id;
   }
   public void setId(Integer id) {
     this.id = id;
   }
   public Integer getUserId() {
     return userId;
   }
   public void setUserId(Integer userId) {
     this.userId = userId;
   }
   public String getNumber() {
     return number;
   }
   public void setNumber(String number) {
     this.number = number == null ? null : number.trim();
   }
   public Date getCreatetime() {
     return createtime;
   }
   public void setCreatetime(Date createtime) {
     this.createtime = createtime;
   }
   public String getNote() {
     return note;
   }
   public void setNote(String note) {
     this.note = note == null ? null : note.trim();
   }
   public User getUser() {
     return user;
   }
   public void setUser(User user) {
     this.user = user;
   }
   public List<Orderdetail> getOrderdetails() {
     return orderdetails;
   }
   public void setOrderdetails(List<Orderdetail> orderdetails) {
     this.orderdetails = orderdetails;
   }  
 }

 <!-- 订单查询关联用户的resultMap,将整个查询结果映射到orders中 -->
   <resultMap type="com.luchao.mybatis.first.po.Orders" id="ordersUserResultMap">
     <id column="id" property="id" />
     <result column="user_id" property="userId" />
     <result column="number" property="number" />
     <result column="createtime" property="createtime" />
     <result column="note" property="note" />
     <!-- 配置映射的关联的用户信息 -->
     <!-- association：用于映射关联查询单个对象的信息 property：要将关联查询的用户信息映射到Orders中哪个属性 -->
     <association property="user" javaType="com.luchao.mybatis.first.po.User">
       <!-- id：关联查询用户的唯 一标识 column：指定唯 一标识用户信息的列 javaType：映射到user的哪个属性 -->
       <id column="user_id" property="id" />
       <result column="username" property="username" />
       <result column="sex" property="sex" />
       <result column="address" property="address" />
     </association>
   </resultMap>
 <select id="findOrderUserMap" resultMap="ordersUserResultMap">
     select
     orders.*,
     user.username,
     user.sex,
     user.address
     from orders,user
     where
     orders.user_id = user.id
   </select>

 //查询订单和用户信息通过resultMap
 public List<Orders> findOrderUserMap() throws Exception;

public void findOrdersUserMap() throws Exception {
     // 获取sqlSession对象
     SqlSession sqlSession = sqlSessionFactory.openSession();
     // 创建OrderMapper对象，MyBatis自动生成mapper代理
     OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class);
     // 调用orderMapper的方法，查询订单和用户信息
     List<Orders> orders = orderMapper.findOrderUserMap();
     System.out.println(orders.size());
 }

 <!-- 订单及订单明细和用户信息的map 使用继承不用在配置订单和用户信息 -->
   <resultMap type="com.luchao.mybatis.first.po.Orders" id="ordersOrderdetailResultMap"
     extends="ordersUserResultMap">
     <collection property="orderdetails"
       ofType="com.luchao.mybatis.first.po.Orderdetail">
       <result column="orderdetail_id" property="id" />
       <result column="items_id" property="itemsId" />
       <result column="items_num" property="itemsNum" />
       <result column="orders_id" property="ordersId" />
     </collection>
   </resultMap>
 <select id="findOrderAndOrderdetailMap" resultMap="ordersOrderdetailResultMap">
     select
     orders.*,
     user.username,
     user.sex,
     user.address,
     orderdetail.id orderdetail_id,
     orderdetail.items_id,
     orderdetail.items_num,
     orderdetail.orders_id
     from
     orders,user,orderdetail
     where orders.user_id = user.id and
     orderdetail.orders_id = orders.id
   </select>

public void findOrderAndOrderdetailMap() throws Exception {
     // 获取sqlSession对象
     SqlSession sqlSession = sqlSessionFactory.openSession();
     // 创建OrderMapper对象，MyBatis自动生成mapper代理
     OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class);
     // 调用orderMapper的方法，查询订单和用户信息
     List<Orders> orders = orderMapper.findOrderAndOrderdetailMap();
     System.out.println(orders.get().getOrderdetails().size());
     System.out.println(orders.size());
   }

public class Orderdetail {
   private Integer id;
   private Integer ordersId;
   private Integer itemsId;
   private Integer itemsNum;
   //商品信息
   private Items items;
   public Integer getId() {
     return id;
   }
   public void setId(Integer id) {
     this.id = id;
   }
   public Integer getOrdersId() {
     return ordersId;
   }
   public void setOrdersId(Integer ordersId) {
     this.ordersId = ordersId;
   }
   public Integer getItemsId() {
     return itemsId;
   }
   public void setItemsId(Integer itemsId) {
     this.itemsId = itemsId;
   }
   public Integer getItemsNum() {
     return itemsNum;
   }
   public void setItemsNum(Integer itemsNum) {
     this.itemsNum = itemsNum;
   }
   public Items getItems() {
     return items;
   }
   public void setItems(Items items) {
     this.items = items;
   }
   @Override
   public String toString() {
     return "Orderdetail [id=" + id + ", ordersId=" + ordersId
         + ", itemsId=" + itemsId + ", itemsNum=" + itemsNum + "]";
   } 
 }

<!-- 查询用户及购买的商品 -->
   <resultMap type="com.luchao.mybatis.first.po.User" id="ordersItemsResultMap">
     <!-- 用户信息 -->
     <id column="user_id" property="id" />
     <result column="username" property="username" />
     <result column="sex" property="sex" />
     <result column="address" property="address" />
     <!-- 订单信息 一个用户对应多个订单，使用collection映射 -->
     <collection property="ordersList" ofType="com.luchao.mybatis.first.po.Orders">
       <id column="id" property="id" />
       <result column="user_id" property="userId" />
       <result column="number" property="number" />
       <result column="createtime" property="createtime" />
       <result column="note" property="note" />
       <!-- 订单明细 一个订单包括 多个明细 -->
       <collection property="orderdetails"
         ofType="com.luchao.mybatis.first.po.Orderdetail">
         <id column="id" property="id" />
         <result column="items_id" property="itemsId" />
         <result column="items_num" property="itemsNum" />
         <result column="orders_id" property="ordersId" />
         <!-- 商品信息 一个订单明细对应一个商品 -->
         <association property="items"
           javaType="com.luchao.mybatis.first.po.Items">
           <id column="items_id" property="id" />
           <result column="items_name" property="name" />
           <result column="items_detail" property="detail" />
           <result column="items_price" property="price" />
         </association>
       </collection>
     </collection>
   </resultMap>
 <select id="findOrderAndItemMap" resultMap="ordersItemsResultMap">
     select
     orders.*,
     user.username,
     user.sex,
     user.address,
     orderdetail.id orderdetail_id,
     orderdetail.items_id,
     orderdetail.items_num,
     orderdetail.orders_id,
     items.id items_id,
     items.name items_name,
     items.detail items_detail,
     items.price items_price
     from orders,user,orderdetail,items
     where orders.user_id =
     user.id and orderdetail.orders_id = orders.id AND orderdetail.items_id
     = items.id
   </select>

 //查询订单、订单明细和用户信息通过resultMap
 public List<User> findOrderAndItemMap() throws Exception;

public void findOrderAndItemMap() throws Exception {
     // 获取sqlSession对象
     SqlSession sqlSession = sqlSessionFactory.openSession();
     // 创建OrderMapper对象，MyBatis自动生成mapper代理
     OrderMapper orderMapper = sqlSession.getMapper(OrderMapper.class);
     // 调用orderMapper的方法，查询订单和用户信息
     List<User> users = orderMapper.findOrderAndItemMap();
     System.out.println(users.get().getOrdersList().get()
         .getOrderdetails().get().getId());
     // System.out.println(orders.size());
 }