Mybatis学习（5）高级映射

需求：

一、一对一查询

查询订单信息，关联查询创建订单的用户信息；

orders--->user：一个订单只由一个用户创建，一对一

orders表 和 user表：

1）使用resultType方法：

思路: 查询订单的同时，关联查询用户信息；创建Order的扩展类，包含订单信息、用户信息；

pojo -- Orders：

package com.cy.po;

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

public class Orders {
    private Integer id;

    private Integer userId;

    private String number;

    private Date createtime;

    private String note;

    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();
    }
}

pojo-- User：

package com.cy.po;

import java.util.Date;

public class User {
    //属性名和数据库表的字段对应
        private int id;
        private String username;// 用户姓名
        private String sex;// 性别
        private Date birthday;// 生日
        private String address;// 地址
        public int getId() {
            return id;
        }
        public void setId(int 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 Date getBirthday() {
            return birthday;
        }
        public void setBirthday(Date birthday) {
            this.birthday = birthday;
        }
        public String getAddress() {
            return address;
        }
        public void setAddress(String address) {
            this.address = address;
        }
        @Override
        public String toString() {
            return "------->> User [id=" + id + ", username=" + username + ", sex=" + sex
                    + ", birthday=" + birthday + ", address=" + address + "]";
        }
}

pojo -- Order扩展类 OrdersCustom：

package com.cy.po;

/**
 * 
 * <p>Description: 订单的扩展类</p>
 */
//通过此类映射订单和用户查询的结果，让此类继承包括 字段较多的pojo类
public class OrdersCustom extends Orders{
    
    //添加用户属性
    /*USER.username,
      USER.sex,
      USER.address */
    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;
    }
    
}

Mapper.xml:

<mapper namespace="com.cy.mapper.OrdersMapperCustom">

    <!-- 查询订单关联查询用户信息 -->
    <select id="findOrdersUser" resultType="com.cy.po.OrdersCustom">
        SELECT orders.*,USER.username,USER.sex,USER.address
        FROM orders,USER
        WHERE orders.user_id = user.id
    </select>
    
</mapper>

Mapper接口：

/**
 * 
 * <p>Title: OrdersMapperCustom</p>
 * <p>Description: 订单mapper</p>
 */
public interface OrdersMapperCustom {
    
    //查询订单关联查询用户信息
    public List<OrdersCustom> findOrdersUser()throws Exception;
    
}

测试代码：

public class OrdersMapperCustomTest {
    private SqlSessionFactory sqlSessionFactory;
    
    @Before
    public void setUp() throws Exception {
        String resource = "SqlMapConfig.xml";
        InputStream inputStream = Resources.getResourceAsStream(resource);
        sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
    }

    @Test
    public void testFindOrdersUser() throws Exception {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        OrdersMapperCustom ordersMapperCustom = sqlSession.getMapper(OrdersMapperCustom.class);
        List<OrdersCustom> list = ordersMapperCustom.findOrdersUser();
        System.out.println(list.toString());
        sqlSession.close();
    }

}

 2）使用resultMap方法：

思路：使用resultMap将查询结果中的订单信息映射到Orders对象中，在orders类中添加User属性，将关联查询出来的用户信息映射到orders对象中的user属性中。

Orders中保存user：

package com.cy.po;

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

public class Orders {
    private Integer id;

    private Integer userId;

    private String number;

    private Date createtime;

    private String note;
    
    private User user;

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    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();
    }
}

Mapper.xml:

<mapper namespace="com.cy.mapper.OrdersMapperCustom">
    <!-- 订单查询关联用户的resultMap 将整个查询的结果映射到com.cy.po.Orders中-->
    <resultMap id="OrdersUserResultMap" type="com.cy.po.Orders">
        <!-- 配置映射的订单信息 -->
        <!-- id：指定查询列中的唯 一标识，订单信息的中的唯 一标识，如果有多个列组成唯一标识，配置多个id
            column：订单信息的唯一标识列
            property：订单信息的唯一标识 列所映射到Orders中哪个属性
          -->
        <id column="id" property="id"></id>
        <result column="user_id" property="userId"></result>
        <result column="number" property="number"></result>
        <result column="createtime" property="createtime"></result>
        <result column="note" property="note"></result>
        <!-- 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.cy.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  property：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>
    
    <!-- 查询订单关联查询用户信息，使用resultmap -->
    <select id="findOrdersUserResultMap" resultMap="OrdersUserResultMap">
        SELECT
        orders.*,
        USER.username,
        USER.sex,
        USER.address
        FROM
        orders,
        USER
        WHERE orders.user_id = user.id
    </select>
    
</mapper>

mapper接口：

//查询订单关联查询用户使用resultMap
public List<Orders> findOrdersUserResultMap()throws Exception;

测试代码：

@Test
    public void testFindOrdersUserResultMap() throws Exception {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        OrdersMapperCustom ordersMapperCustom = sqlSession.getMapper(OrdersMapperCustom.class);
        
        List<Orders> orders = ordersMapperCustom.findOrdersUserResultMap();
        System.out.println(orders);
        sqlSession.close();
    }

使用resultType和resultMap实现一对一查询的总结：

resultType：使用resultType实现较为简单，如果pojo中没有包括查询出来的列名，需要增加列名对应的属性，即可完成映射。

resultMap：需要单独定义resultMap，如果对查询结果有特殊的要求，使用resultMap可以完成将关联查询映射pojo的属性中。

resultMap可以实现延迟加载，resultType无法实现延迟加载。

二、一对多查询

需求：查询订单及订单明细的信息。

在orders.java类中添加List<orderDetail> orderDetails属性：

package com.cy.po;

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

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;
    
    private List<Orderdetail> orderdetails;
    
    public List<Orderdetail> getOrderdetails() {
        return orderdetails;
    }

    public void setOrderdetails(List<Orderdetail> orderdetails) {
        this.orderdetails = orderdetails;
    }

    public User getUser() {
        return user;
    }

    public void setUser(User user) {
        this.user = user;
    }

    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();
    }
}

package com.cy.po;

public class Orderdetail {
    private Integer id;

    private Integer ordersId;

    private Integer itemsId;

    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 + "]";
    }
    
}

mapper.xml:

<mapper namespace="com.cy.mapper.OrdersMapperCustom">
    <!-- 订单及订单明细的resultMap 使用extends继承，不用在中配置订单信息和用户信息的映射 -->
    <resultMap id="OrdersAndOrderDetailResultMap" type="com.cy.po.Orders" extends="OrdersUserResultMap" >
        <!-- 订单信息 --><!-- 用户信息 --><!-- 使用extends继承，不用在中配置订单信息和用户信息的映射 -->
        
        <!-- 订单明细信息 一个订单关联查询出了多条明细，要使用collection进行映射
        collection：对关联查询到多条记录映射到集合对象中
        property：将关联查询到多条记录映射到com.cy.po.Orders哪个属性
        ofType：指定映射到list集合属性中pojo的类型
         -->
        <collection property="orderdetails" ofType="com.cy.po.Orderdetail">
            <!-- id：订单明细唯一标识 property:要将订单明细的唯 一标识映射到com.cy.po.Orderdetail的哪个属性 -->
            <id column="orderdetail_id" property="id"></id>
            <result column="items_id" property="itemsId"/>
            <result column="items_num" property="itemsNum"/>
            <result column="orders_id" property="ordersId"/>
        </collection>
    </resultMap>
    <!-- 查询订单关联查询用户及订单明细，使用resultmap -->
    <select id="findOrdersAndOrderDetailResultMap" resultMap="OrdersAndOrderDetailResultMap">
        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>
    
</mapper>

mapper接口：

//查询订单(关联用户)及订单明细
public List<Orders> findOrdersAndOrderDetailResultMap() throws Exception;

测试代码：

@Test
    public void FindOrdersAndOrderDetailResultMap() throws Exception {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        OrdersMapperCustom ordersMapperCustom = sqlSession.getMapper(OrdersMapperCustom.class);
        
        List<Orders> orders = ordersMapperCustom.findOrdersAndOrderDetailResultMap();
        System.out.println(orders);
        sqlSession.close();
    }

三、多对多查询

需求：查询用户及用户购买商品信息

思路：

将用户信息映射到user中。

在user类中添加订单列表属性List<Orders> orderslist，将用户创建的订单映射到orderslist

在Orders中添加订单明细列表属性List<OrderDetail>orderdetials，将订单的明细映射到orderdetials

在OrderDetail中添加Items属性，将订单明细所对应的商品映射到Items

在上面代码基础上，User类中添加List<Orders> orderslist:

package com.cy.po;

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

public class User {
    //属性名和数据库表的字段对应
        private int id;
        private String username;// 用户姓名
        private String sex;// 性别
        private Date birthday;// 生日
        private String address;// 地址
        
        private List<Orders> orderslist;
        
        public List<Orders> getOrderslist() {
            return orderslist;
        }
        public void setOrderslist(List<Orders> orderslist) {
            this.orderslist = orderslist;
        }
        public int getId() {
            return id;
        }
        public void setId(int 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 Date getBirthday() {
            return birthday;
        }
        public void setBirthday(Date birthday) {
            this.birthday = birthday;
        }
        public String getAddress() {
            return address;
        }
        public void setAddress(String address) {
            this.address = address;
        }
        @Override
        public String toString() {
            return "------->> User [id=" + id + ", username=" + username + ", sex=" + sex
                    + ", birthday=" + birthday + ", address=" + address + "]";
        }
}

mapper.xml:

<mapper namespace="com.cy.mapper.OrdersMapperCustom">
    <!-- 查询用户及购买的商品 -->
    <resultMap type="com.cy.po.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"/>
        
        <!-- 订单信息 一个用户对应多个订单，使用collection映射-->
        <collection property="orderslist" ofType="com.cy.po.Orders">
            <id column="id" property="id"></id>
            <result column="user_id" property="userId"></result>
            <result column="number" property="number"></result>
            <result column="createtime" property="createtime"></result>
            <result column="note" property="note"></result>
            <!-- 订单明细 一个订单包括 多个明细-->
            <collection property="orderdetails" ofType="com.cy.po.Orderdetail">
                <id column="orderdetail_id" property="id"></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.cy.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>
    <!-- 查询用户及购买的商品信息，使用resultmap -->
    <select id="findUserAndItemsResultMap" resultMap="UserAndItemsResultMap">
        SELECT 
          orders.*,
          USER.username,
          USER.sex,
          USER.address,
          orderdetail.id orderdetail_id,
          orderdetail.items_id,
          orderdetail.items_num,
          orderdetail.orders_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>
    
</mapper>

上面，其实思路就是用户中保存List<Orders>,然后Order中有多个订单明细List<Orderdetail>;一个订单明细对应一个商品，private Item;

顺着写来来就是了，不难。

mapper接口：

//查询用户购买商品信息
public List<User> findUserAndItemsResultMap() throws Exception;

测试代码：

@Test
    public void FindUserAndItemsResultMap() throws Exception {
        SqlSession sqlSession = sqlSessionFactory.openSession();
        OrdersMapperCustom ordersMapperCustom = sqlSession.getMapper(OrdersMapperCustom.class);
        
        List<User> users = ordersMapperCustom.findUserAndItemsResultMap();
        System.out.println(users);
        sqlSession.close();
    }

多对多查询总结：

将查询用户购买的商品信息明细清单，（用户名、用户地址、购买商品名称、购买商品时间、购买商品数量）

针对上边的需求就使用resultType将查询到的记录映射到一个扩展的pojo中，很简单实现明细清单的功能。