mybatis的一对多和多对多查询

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.csdn.net/preferG/article/details/78335382

一对多和多对多的关系

我是以你平时买东西为例子的，一个用户对应多个订单，一个订单对应多个订单明细，一个订单明细对应一个商品，根据这些关系来进行实例演示。

实例演示

1. 一对多（一个订单对应多个订单明细） 
   1）定义一个用户实体类User.java

package com;

import java.util.Date;
import java.util.List;
public class User {
    private Integer id;
    // 姓名
    private String username;
    // 性别
    private String sex;
    // 地址
    private String address;
    // 生日
    private Date birthday;
    // 用户创建的订单列表
    private List<Orders> ordersList;
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    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;
    }
    public Date getBirthday() {
        return birthday;
    }
    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
    public List<Orders> getOrdersList() {
        return ordersList;
    }
    public void setOrdersList(List<Orders> ordersList) {
        this.ordersList = ordersList;
    }
    @Override
    public String toString() {
        return "User [id=" + id + ", username=" + username + ", sex=" + sex
                + ", address=" + address + ", birthday=" + birthday + "]";
    }

}

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10
• 11
• 12
• 13
• 14
• 15
• 16
• 17
• 18
• 19
• 20
• 21
• 22
• 23
• 24
• 25
• 26
• 27
• 28
• 29
• 30
• 31
• 32
• 33
• 34
• 35
• 36
• 37
• 38
• 39
• 40
• 41
• 42
• 43
• 44
• 45
• 46
• 47
• 48
• 49
• 50
• 51
• 52
• 53
• 54
• 55
• 56
• 57
• 58
• 59

2)定义一个订单实体类Order.java

package com;

import java.util.Date;
import java.util.List;

public class Orders {
    /** 主键订单Id */
    private Integer id;
    /** 下单用户id */
    private Integer userid;
    /** 订单号 */
    private String number;
    /** 创建订单时间 */
    private Date createTime;
    /** 备注 */
    private String note;
    // 用户信息
    private User user;
    // 订单明细
    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;
    }
    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;
    }
    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;
    }
    @Override
    public String toString() {
        return "Orders [id=" + id + ", userid=" + userid + ", number=" + number
                + ", createTime=" + createTime + ", note=" + note + ", user="
                + user + "]";
    }
}

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10
• 11
• 12
• 13
• 14
• 15
• 16
• 17
• 18
• 19
• 20
• 21
• 22
• 23
• 24
• 25
• 26
• 27
• 28
• 29
• 30
• 31
• 32
• 33
• 34
• 35
• 36
• 37
• 38
• 39
• 40
• 41
• 42
• 43
• 44
• 45
• 46
• 47
• 48
• 49
• 50
• 51
• 52
• 53
• 54
• 55
• 56
• 57
• 58
• 59
• 60
• 61
• 62
• 63
• 64
• 65
• 66
• 67
• 68
• 69
• 70

3)订单明细实体类 OrderDetail.java

package com;

public class OrderDetail {
    /** 主鍵，明细表Id */
    private Integer id;
    /** 訂單Id */
    private Integer ordersId;
    /** 商品id */
    private Integer itemsId;
    /** 商品购买数量 */
    private Integer itemsNum;
    // 明细对应的商品信息
    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 + "]";
    }

}

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10
• 11
• 12
• 13
• 14
• 15
• 16
• 17
• 18
• 19
• 20
• 21
• 22
• 23
• 24
• 25
• 26
• 27
• 28
• 29
• 30
• 31
• 32
• 33
• 34
• 35
• 36
• 37
• 38
• 39
• 40
• 41
• 42
• 43
• 44
• 45
• 46
• 47
• 48
• 49
• 50

4)商品实体类

package com;

import java.util.Date;

public class Items {
     /** 商品表主键Id */
    private Integer id;
    /** 商品名称 */
    private String itemsName;
    /** 商品定价 */
    private float price;
    /** 商品描述 */
    private String detail;
    /** 商品图片 */
    private String picture;
    /** 生产日期 */
    private Date createTime;
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getItemsName() {
        return itemsName;
    }
    public void setItemsName(String itemsName) {
        this.itemsName = itemsName;
    }
    public float getPrice() {
        return price;
    }
    public void setPrice(float price) {
        this.price = price;
    }
    public String getDetail() {
        return detail;
    }
    public void setDetail(String detail) {
        this.detail = detail;
    }
    public String getPicture() {
        return picture;
    }
    public void setPicture(String picture) {
        this.picture = picture;
    }
    public Date getCreateTime() {
        return createTime;
    }
    public void setCreateTime(Date createTime) {
        this.createTime = createTime;
    }
    @Override
    public String toString() {
        return "Items [id=" + id + ", itemsName=" + itemsName + ", price="
                + price + ", detail=" + detail + ", picture=" + picture
                + ", createTime=" + createTime + "]";
    }
}

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10
• 11
• 12
• 13
• 14
• 15
• 16
• 17
• 18
• 19
• 20
• 21
• 22
• 23
• 24
• 25
• 26
• 27
• 28
• 29
• 30
• 31
• 32
• 33
• 34
• 35
• 36
• 37
• 38
• 39
• 40
• 41
• 42
• 43
• 44
• 45
• 46
• 47
• 48
• 49
• 50
• 51
• 52
• 53
• 54
• 55
• 56
• 57
• 58
• 59
• 60
• 61

5）几个实体类写完了之后根据他们的关系来进行编写对应的mapper.xml文件了。 
一个订单对应多个订单明细对应的OrdersCustomMapper.xml

<mapper namespace="com.OrdersCustomMapper">
    <!-- 一对多查询，一个订单对应多个订单明细 -->
    <select id="findOrdersAndOrderDetailResultMap" resultMap="ordersAndOrderDetailResultMap">
        SELECT 
                  t1.*,
                  t2.username,
                  t2.sex,
                  t2.address,
                  t3.id orderdetail_id,
                  t3.items_id,
                  t3.items_num,
                  t3.orders_id
            FROM
                  orders t1,
                  t_user t2,
                  orderdetail t3
            WHERE t1.user_id = t2.id AND t3.orders_id=t1.id
    </select> 
    <resultMap type="com.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"/>
         <!-- 订单关联用户 -->
         <association property="user" javaType="com.User">
            <id column="user_id" property="id"/>
             <result column="username" property="username"/>
             <result column="sex" property="sex"/>
             <result column="address" property="address"/>
         </association>
    </resultMap> 
</mapper> 

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10
• 11
• 12
• 13
• 14
• 15
• 16
• 17
• 18
• 19
• 20
• 21
• 22
• 23
• 24
• 25
• 26
• 27
• 28
• 29
• 30
• 31
• 32
• 33

6)OrdersCustomMapper.xml文件完成之后编写OrdersCustomMapper.java文件(面向接口编程的，这个类的路径就是OrdersCustomMapper.xml中命名空间的名字，其中的方法就是OrdersCustomMapper.xml中的select的id对应的方法)

package com;

import java.util.List;

public interface OrdersCustomMapper {

    /**查询订单以及订单明细**/
    public List<OrdersCustom> findOrdersAndOrderDetailResultMap();
}

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9

7)测试类Test.java

package pojo;

import java.io.IOException;
import java.io.Reader;
import java.util.List;
import java.util.Map;

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 com.OrdersCustom;
import com.OrdersCustomMapper;
import com.Student;
import com.User;

public class Test {
    public static void main(String[] args) throws IOException {
        String resource = "sqlConfig.xml";
        Reader reader = Resources.getResourceAsReader(resource);
        SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader);
        SqlSession session = sqlMapper.openSession();
//      Student student = new Student();
//      session.insert("com.StudentMapper.insertStudent", student); //插入操作
//      session.select("com.StudentMapper.selectStudent",student); //查询操作
//      List<Student> students = session.selectList("com.StudentMapper.selectStudent");
//      session.commit();
//      System.out.println(students);
        //Map<String, Object> map = session.select("com.StudentMapper.selectUsers", null);
//      Map<String, Object> map = session.selectMap("com.StudentMapper.selectUsers","id");//resultMap方法查询
//      System.out.println("集合的长度="+map.size());
//      System.out.println(map);
        /**一对一查询，一个订单对应一个用户**/
        OrdersCustomMapper oc = session.getMapper(OrdersCustomMapper.class);
        List<OrdersCustom> list = oc.findOrdersUser();
        System.out.println(list);
        /**一对多查询，一个订单对应多个订单明细**/
        List<OrdersCustom> list2 = oc.findOrdersAndOrderDetailResultMap();
        System.out.println("list2="+list2);
        /**多对多查询，一个用户对应多个订单，一个订单对应多个订单明细，一个订单明细对应一个商品 **/
        List<User> list3 = oc.findUserAndItemsResultMap();
        System.out.println("list3="+list3);
    }
}

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10
• 11
• 12
• 13
• 14
• 15
• 16
• 17
• 18
• 19
• 20
• 21
• 22
• 23
• 24
• 25
• 26
• 27
• 28
• 29
• 30
• 31
• 32
• 33
• 34
• 35
• 36
• 37
• 38
• 39
• 40
• 41
• 42
• 43
• 44
• 45
• 46

1. 多对多其实跟一对多差不多，只不过修改一下OrdersCustomMapper.xml中的内容即可修改如下

<?xml version="1.0" encoding="UTF-8" ?> 
       <!DOCTYPE mapper 
          PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
          "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.OrdersCustomMapper">
    <!-- 一对一查询 ，一个订单对应一个用户-->
    <select id="findOrdersUser" resultType="com.OrdersCustom" resultMap="OrdersUserResultMap">
    SELECT t1.*,
       t2.username,
       t2.sex,
       t2.address
    FROM
        orders t1,
        t_user t2
    WHERE t1.user_id=t2.id
    </select>
    <!-- 一对多查询，一个订单对应多个订单明细 -->
    <select id="findOrdersAndOrderDetailResultMap" resultMap="ordersAndOrderDetailResultMap">
        SELECT 
                  t1.*,
                  t2.username,
                  t2.sex,
                  t2.address,
                  t3.id orderdetail_id,
                  t3.items_id,
                  t3.items_num,
                  t3.orders_id
            FROM
                  orders t1,
                  t_user t2,
                  orderdetail t3
            WHERE t1.user_id = t2.id AND t3.orders_id=t1.id
    </select>
    <!-- 多对多查询，查询用户以及用户购买的商品信息，一个用户对应多个订单，一个订单对应多个订单明细，一个订单明细对应一个商品 -->
    <select id="findUserAndItemsResultMap" resultMap="userAndItemsResultMap">
        SELECT 
                   t1.*,
                   t2.username,
                   t2.sex,
                   t2.address,
                   t3.id orderdetail_id,
                   t3.items_id,
                   t3.items_num,
                   t3.orders_id,
                   t4.itemsname items_name,
                   t4.detail items_detail,
                   t4.price items_price
            FROM
                  orders t1,
                  t_user t2,
                  orderdetail t3,
                  items t4
            WHERE t1.user_id =  t2.id AND  t3.orders_id=t1.id AND t3.items_id = t4.id
    </select>
    <resultMap type="com.User" id="userAndItemsResultMap">
        <!-- 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"/>
        <!-- 一个用户对应多个订单 -->
        <collection property="ordersList" ofType="com.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"/>
                <!-- 一个订单对应多个订单明细 -->
                <collection property="orderdetails" ofType="com.OrderDetail">
                    <id column="orderdetail_id" property="id"/>
                    <result column="items_id"   property="itemsId"/>
                    <result column="items_num"  property="itemsNum"/>
                    <result column="orders_id"  property="ordersId"/>
                    <!-- 一个订单明细对应一个商品 -->
                    <association property="items" javaType="com.Items">
                        <id column="items_id" property="id"/>
                        <result column="items_name" property="itemsName"/>
                        <result column="items_detail" property="detail"/>
                        <result column="items_price" property="price"/>
                    </association>
                </collection>
         </collection>
    </resultMap>
    <resultMap type="com.Orders" id="ordersAndOrderDetailResultMap">
        <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"/>
         <!-- 订单关联用户 -->
         <association property="user" javaType="com.User">
            <id column="user_id" property="id"/>
             <result column="username" property="username"/>
             <result column="sex" property="sex"/>
             <result column="address" property="address"/>
         </association>
         <!-- 关联订单详细 -->
         <collection property="orderdetails" ofType="com.OrderDetail">
            <id 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>
    <resultMap type="com.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"/>
         <!-- 订单关联用户 -->
         <association property="user" javaType="com.User">
            <id column="user_id" property="id"/>
             <result column="username" property="username"/>
             <result column="sex" property="sex"/>
             <result column="address" property="address"/>
         </association>
    </resultMap>
</mapper> 

一对多和多对多的关系

我是以你平时买东西为例子的，一个用户对应多个订单，一个订单对应多个订单明细，一个订单明细对应一个商品，根据这些关系来进行实例演示。

实例演示

1. 一对多（一个订单对应多个订单明细） 
   1）定义一个用户实体类User.java

package com;

import java.util.Date;
import java.util.List;
public class User {
    private Integer id;
    // 姓名
    private String username;
    // 性别
    private String sex;
    // 地址
    private String address;
    // 生日
    private Date birthday;
    // 用户创建的订单列表
    private List<Orders> ordersList;
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    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;
    }
    public Date getBirthday() {
        return birthday;
    }
    public void setBirthday(Date birthday) {
        this.birthday = birthday;
    }
    public List<Orders> getOrdersList() {
        return ordersList;
    }
    public void setOrdersList(List<Orders> ordersList) {
        this.ordersList = ordersList;
    }
    @Override
    public String toString() {
        return "User [id=" + id + ", username=" + username + ", sex=" + sex
                + ", address=" + address + ", birthday=" + birthday + "]";
    }

}

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10
• 11
• 12
• 13
• 14
• 15
• 16
• 17
• 18
• 19
• 20
• 21
• 22
• 23
• 24
• 25
• 26
• 27
• 28
• 29
• 30
• 31
• 32
• 33
• 34
• 35
• 36
• 37
• 38
• 39
• 40
• 41
• 42
• 43
• 44
• 45
• 46
• 47
• 48
• 49
• 50
• 51
• 52
• 53
• 54
• 55
• 56
• 57
• 58
• 59

2)定义一个订单实体类Order.java

package com;

import java.util.Date;
import java.util.List;

public class Orders {
    /** 主键订单Id */
    private Integer id;
    /** 下单用户id */
    private Integer userid;
    /** 订单号 */
    private String number;
    /** 创建订单时间 */
    private Date createTime;
    /** 备注 */
    private String note;
    // 用户信息
    private User user;
    // 订单明细
    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;
    }
    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;
    }
    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;
    }
    @Override
    public String toString() {
        return "Orders [id=" + id + ", userid=" + userid + ", number=" + number
                + ", createTime=" + createTime + ", note=" + note + ", user="
                + user + "]";
    }
}

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10
• 11
• 12
• 13
• 14
• 15
• 16
• 17
• 18
• 19
• 20
• 21
• 22
• 23
• 24
• 25
• 26
• 27
• 28
• 29
• 30
• 31
• 32
• 33
• 34
• 35
• 36
• 37
• 38
• 39
• 40
• 41
• 42
• 43
• 44
• 45
• 46
• 47
• 48
• 49
• 50
• 51
• 52
• 53
• 54
• 55
• 56
• 57
• 58
• 59
• 60
• 61
• 62
• 63
• 64
• 65
• 66
• 67
• 68
• 69
• 70

3)订单明细实体类 OrderDetail.java

package com;

public class OrderDetail {
    /** 主鍵，明细表Id */
    private Integer id;
    /** 訂單Id */
    private Integer ordersId;
    /** 商品id */
    private Integer itemsId;
    /** 商品购买数量 */
    private Integer itemsNum;
    // 明细对应的商品信息
    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 + "]";
    }

}

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10
• 11
• 12
• 13
• 14
• 15
• 16
• 17
• 18
• 19
• 20
• 21
• 22
• 23
• 24
• 25
• 26
• 27
• 28
• 29
• 30
• 31
• 32
• 33
• 34
• 35
• 36
• 37
• 38
• 39
• 40
• 41
• 42
• 43
• 44
• 45
• 46
• 47
• 48
• 49
• 50

4)商品实体类

package com;

import java.util.Date;

public class Items {
     /** 商品表主键Id */
    private Integer id;
    /** 商品名称 */
    private String itemsName;
    /** 商品定价 */
    private float price;
    /** 商品描述 */
    private String detail;
    /** 商品图片 */
    private String picture;
    /** 生产日期 */
    private Date createTime;
    public Integer getId() {
        return id;
    }
    public void setId(Integer id) {
        this.id = id;
    }
    public String getItemsName() {
        return itemsName;
    }
    public void setItemsName(String itemsName) {
        this.itemsName = itemsName;
    }
    public float getPrice() {
        return price;
    }
    public void setPrice(float price) {
        this.price = price;
    }
    public String getDetail() {
        return detail;
    }
    public void setDetail(String detail) {
        this.detail = detail;
    }
    public String getPicture() {
        return picture;
    }
    public void setPicture(String picture) {
        this.picture = picture;
    }
    public Date getCreateTime() {
        return createTime;
    }
    public void setCreateTime(Date createTime) {
        this.createTime = createTime;
    }
    @Override
    public String toString() {
        return "Items [id=" + id + ", itemsName=" + itemsName + ", price="
                + price + ", detail=" + detail + ", picture=" + picture
                + ", createTime=" + createTime + "]";
    }
}

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10
• 11
• 12
• 13
• 14
• 15
• 16
• 17
• 18
• 19
• 20
• 21
• 22
• 23
• 24
• 25
• 26
• 27
• 28
• 29
• 30
• 31
• 32
• 33
• 34
• 35
• 36
• 37
• 38
• 39
• 40
• 41
• 42
• 43
• 44
• 45
• 46
• 47
• 48
• 49
• 50
• 51
• 52
• 53
• 54
• 55
• 56
• 57
• 58
• 59
• 60
• 61

5）几个实体类写完了之后根据他们的关系来进行编写对应的mapper.xml文件了。 
一个订单对应多个订单明细对应的OrdersCustomMapper.xml

<mapper namespace="com.OrdersCustomMapper">
    <!-- 一对多查询，一个订单对应多个订单明细 -->
    <select id="findOrdersAndOrderDetailResultMap" resultMap="ordersAndOrderDetailResultMap">
        SELECT 
                  t1.*,
                  t2.username,
                  t2.sex,
                  t2.address,
                  t3.id orderdetail_id,
                  t3.items_id,
                  t3.items_num,
                  t3.orders_id
            FROM
                  orders t1,
                  t_user t2,
                  orderdetail t3
            WHERE t1.user_id = t2.id AND t3.orders_id=t1.id
    </select> 
    <resultMap type="com.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"/>
         <!-- 订单关联用户 -->
         <association property="user" javaType="com.User">
            <id column="user_id" property="id"/>
             <result column="username" property="username"/>
             <result column="sex" property="sex"/>
             <result column="address" property="address"/>
         </association>
    </resultMap> 
</mapper> 

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10
• 11
• 12
• 13
• 14
• 15
• 16
• 17
• 18
• 19
• 20
• 21
• 22
• 23
• 24
• 25
• 26
• 27
• 28
• 29
• 30
• 31
• 32
• 33

6)OrdersCustomMapper.xml文件完成之后编写OrdersCustomMapper.java文件(面向接口编程的，这个类的路径就是OrdersCustomMapper.xml中命名空间的名字，其中的方法就是OrdersCustomMapper.xml中的select的id对应的方法)

package com;

import java.util.List;

public interface OrdersCustomMapper {

    /**查询订单以及订单明细**/
    public List<OrdersCustom> findOrdersAndOrderDetailResultMap();
}

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9

7)测试类Test.java

package pojo;

import java.io.IOException;
import java.io.Reader;
import java.util.List;
import java.util.Map;

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 com.OrdersCustom;
import com.OrdersCustomMapper;
import com.Student;
import com.User;

public class Test {
    public static void main(String[] args) throws IOException {
        String resource = "sqlConfig.xml";
        Reader reader = Resources.getResourceAsReader(resource);
        SqlSessionFactory sqlMapper = new SqlSessionFactoryBuilder().build(reader);
        SqlSession session = sqlMapper.openSession();
//      Student student = new Student();
//      session.insert("com.StudentMapper.insertStudent", student); //插入操作
//      session.select("com.StudentMapper.selectStudent",student); //查询操作
//      List<Student> students = session.selectList("com.StudentMapper.selectStudent");
//      session.commit();
//      System.out.println(students);
        //Map<String, Object> map = session.select("com.StudentMapper.selectUsers", null);
//      Map<String, Object> map = session.selectMap("com.StudentMapper.selectUsers","id");//resultMap方法查询
//      System.out.println("集合的长度="+map.size());
//      System.out.println(map);
        /**一对一查询，一个订单对应一个用户**/
        OrdersCustomMapper oc = session.getMapper(OrdersCustomMapper.class);
        List<OrdersCustom> list = oc.findOrdersUser();
        System.out.println(list);
        /**一对多查询，一个订单对应多个订单明细**/
        List<OrdersCustom> list2 = oc.findOrdersAndOrderDetailResultMap();
        System.out.println("list2="+list2);
        /**多对多查询，一个用户对应多个订单，一个订单对应多个订单明细，一个订单明细对应一个商品 **/
        List<User> list3 = oc.findUserAndItemsResultMap();
        System.out.println("list3="+list3);
    }
}

• 1
• 2
• 3
• 4
• 5
• 6
• 7
• 8
• 9
• 10
• 11
• 12
• 13
• 14
• 15
• 16
• 17
• 18
• 19
• 20
• 21
• 22
• 23
• 24
• 25
• 26
• 27
• 28
• 29
• 30
• 31
• 32
• 33
• 34
• 35
• 36
• 37
• 38
• 39
• 40
• 41
• 42
• 43
• 44
• 45
• 46

1. 多对多其实跟一对多差不多，只不过修改一下OrdersCustomMapper.xml中的内容即可修改如下

<?xml version="1.0" encoding="UTF-8" ?> 
       <!DOCTYPE mapper 
          PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
          "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.OrdersCustomMapper">
    <!-- 一对一查询 ，一个订单对应一个用户-->
    <select id="findOrdersUser" resultType="com.OrdersCustom" resultMap="OrdersUserResultMap">
    SELECT t1.*,
       t2.username,
       t2.sex,
       t2.address
    FROM
        orders t1,
        t_user t2
    WHERE t1.user_id=t2.id
    </select>
    <!-- 一对多查询，一个订单对应多个订单明细 -->
    <select id="findOrdersAndOrderDetailResultMap" resultMap="ordersAndOrderDetailResultMap">
        SELECT 
                  t1.*,
                  t2.username,
                  t2.sex,
                  t2.address,
                  t3.id orderdetail_id,
                  t3.items_id,
                  t3.items_num,
                  t3.orders_id
            FROM
                  orders t1,
                  t_user t2,
                  orderdetail t3
            WHERE t1.user_id = t2.id AND t3.orders_id=t1.id
    </select>
    <!-- 多对多查询，查询用户以及用户购买的商品信息，一个用户对应多个订单，一个订单对应多个订单明细，一个订单明细对应一个商品 -->
    <select id="findUserAndItemsResultMap" resultMap="userAndItemsResultMap">
        SELECT 
                   t1.*,
                   t2.username,
                   t2.sex,
                   t2.address,
                   t3.id orderdetail_id,
                   t3.items_id,
                   t3.items_num,
                   t3.orders_id,
                   t4.itemsname items_name,
                   t4.detail items_detail,
                   t4.price items_price
            FROM
                  orders t1,
                  t_user t2,
                  orderdetail t3,
                  items t4
            WHERE t1.user_id =  t2.id AND  t3.orders_id=t1.id AND t3.items_id = t4.id
    </select>
    <resultMap type="com.User" id="userAndItemsResultMap">
        <!-- 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"/>
        <!-- 一个用户对应多个订单 -->
        <collection property="ordersList" ofType="com.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"/>
                <!-- 一个订单对应多个订单明细 -->
                <collection property="orderdetails" ofType="com.OrderDetail">
                    <id column="orderdetail_id" property="id"/>
                    <result column="items_id"   property="itemsId"/>
                    <result column="items_num"  property="itemsNum"/>
                    <result column="orders_id"  property="ordersId"/>
                    <!-- 一个订单明细对应一个商品 -->
                    <association property="items" javaType="com.Items">
                        <id column="items_id" property="id"/>
                        <result column="items_name" property="itemsName"/>
                        <result column="items_detail" property="detail"/>
                        <result column="items_price" property="price"/>
                    </association>
                </collection>
         </collection>
    </resultMap>
    <resultMap type="com.Orders" id="ordersAndOrderDetailResultMap">
        <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"/>
         <!-- 订单关联用户 -->
         <association property="user" javaType="com.User">
            <id column="user_id" property="id"/>
             <result column="username" property="username"/>
             <result column="sex" property="sex"/>
             <result column="address" property="address"/>
         </association>
         <!-- 关联订单详细 -->
         <collection property="orderdetails" ofType="com.OrderDetail">
            <id 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>
    <resultMap type="com.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"/>
         <!-- 订单关联用户 -->
         <association property="user" javaType="com.User">
            <id column="user_id" property="id"/>
             <result column="username" property="username"/>
             <result column="sex" property="sex"/>
             <result column="address" property="address"/>
         </association>
    </resultMap>
</mapper>