java mybatis lambdaQuery 关联表查询 mybatis关联查询映射

xml

<?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">

<!-- namespace命名空间等于mapper接口地址 -->
<mapper namespace="com.mybatis.mapper.OrdersMapperCustom">

    <!-- type：结果映射到com.mybatis.po.Orders中 -->
    <resultMap type="com.mybatis.po.Orders" id="OrdersUserResultMap">
        <!-- 配置映射关系 -->
        <!-- 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：查询结果列
            property：对象属性
          -->
        <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 多对1
        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.mybatis.po.User">
            <id column="user_id" property="id"/>
            <result column="username" property="username"/>
            <result column="sex" property="sex"/>
            <result column="address" property="address"/>
        </association>
    </resultMap>

    <!-- 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 type="com.mybatis.po.Orders" id="OrdersAndOrderDetailResultMap" extends="OrdersUserResultMap">
        <!-- 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 1对多
        property：将关联查询到多条记录映射到cn.itcast.mybatis.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.mybatis.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.mybatis.po.Orderdetail的哪个属性
              -->
            <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>

    <!-- 查询用户及购买的商品 -->
    <resultMap type="com.mybatis.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.mybatis.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.mybatis.po.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"/>

                    <!-- 商品信息 一个订单明细对应一个商品 -->
                <association property="items" javaType="com.mybatis.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>

    <!-- 查询订单与关联的用户信息 多对1-->
    <select id="findOrdersUser" resultType="com.mybatis.po.OrdersCustom">
        SELECT
        orders.*,
        USER.username,
        USER.sex,
        USER.address
        FROM
        orders,
        USER
        WHERE orders.user_id = user.id
    </select>

    <!-- 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>

    <!-- 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>

    <!-- 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>

    <!-- 延迟加载的resultMap -->
    <resultMap type="com.mybatis.po.Orders" id="OrdersUserLazyLoadingResultMap">
            <!--对订单信息进行映射配置  -->
            <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"/>
            <!-- 实现对用户信息进行延迟加载
            select：指定延迟加载需要执行的statement的id（是根据user_id查询用户信息的statement）
            要使用userMapper.xml中findUserById完成根据用户id(user_id)用户信息的查询，如果findUserById不在本mapper中需要前边加namespace
            column：订单信息中关联用户信息查询的列，是user_id
            关联查询的sql理解为：
            SELECT orders.*,
    (SELECT username FROM USER WHERE orders.user_id = user.id)username,
    (SELECT sex FROM USER WHERE orders.user_id = user.id)sex
     FROM orders
             -->
            <association property="user"  javaType="com.mybatis.po.User"
             select="com.mybatis.mapper.UserMapper.findUserById" column="user_id">
            <!-- 实现对用户信息进行延迟加载 -->
            </association>
    </resultMap>

    <!-- 查询订单关联查询用户，用户信息需要延迟加载 -->
    <select id="findOrdersUserLazyLoading" resultMap="OrdersUserLazyLoadingResultMap">
        SELECT * FROM orders
    </select>
</mapper>

mapper

OrdersMapperCustom.java

package com.mybatis.mapper;

import java.util.List;

import com.mybatis.po.Orders;
import com.mybatis.po.OrdersCustom;
import com.mybatis.po.User;

public interface OrdersMapperCustom {
    //查询订单关联查询用户信息
    public List<OrdersCustom> findOrdersUser()throws Exception;
    //查询订单关联查询用户使用resultMap
    public List<Orders> findOrdersUserResultMap()throws Exception;
    //查询订单(关联用户)及订单明细
    public List<Orders>  findOrdersAndOrderDetailResultMap()throws Exception;
    //查询用户购买商品信息
    public List<User>  findUserAndItemsResultMap()throws Exception;
    //查询订单关联查询用户，用户信息是延迟加载
    public List<Orders> findOrdersUserLazyLoading()throws Exception;
}

po

OrdersCustom.java

package com.mybatis.po;

//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{

    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;
    }
}

Orders.java

package com.mybatis.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;

    //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 == 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;
    }
}

Orderdetail.java

package com.mybatis.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;
    }
}

Items.java

package com.mybatis.po;

import java.util.Date;

public class Items {
    private Integer id;
    private String name;
    private Float price;
    private String pic;
    private Date createtime;
    private String 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 == null ? null : name.trim();
    }

    public Float getPrice() {
        return price;
    }

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

    public String getPic() {
        return pic;
    }

    public void setPic(String pic) {
        this.pic = pic == null ? null : pic.trim();
    }

    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 == null ? null : detail.trim();
    }

}

User.java

package com.mybatis.po;

import java.io.Serializable;
import java.util.Date;
import java.util.List;

public class User implements Serializable {

    //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

    //用户创建的订单列表
    private List<Orders> 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;
    }

    public List<Orders> getOrdersList() {
        return ordersList;
    }
    public void setOrdersList(List<Orders> ordersList) {
        this.ordersList = ordersList;
    }
}