mybatis系列-tkmybatis-05-使用xml方式扩展接口，进行多表关联查询

本文主要是介绍mybatis系列-tkmybatis-05-使用xml方式扩展接口，进行多表关联查询，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

tkMybatis是对Mybatis功能的扩展，在Mybatis中，可以通过xml方式扩展接口（先在*mapper接口类中定义新的接口方法，然后在*mapper.xml文件写实现SQL）。在tkMybatis中，并没有改变Mybatis的作用机制，在常规Mybatis扫描xml文件和mapper文件创建sqlSessionFactory和各种Mapper代理类之后，才进行的扩展，所以以前Mybatis的那一套机制依旧有效。

这里举例说明下，如何基于xml扩展，实现多表关联查询。现在有个Users（用户表）和Orders表（订单表），Orders表中user_id表示下订单的用户id，与Users表的id字段相对应。

1、增加新的Pojo类

该类继承自Users类，然后补充了几个Orders表中的字段

package com.example.demotkmybatisgeneralsecond.pojo;import javax.persistence.Column;import javax.persistence.Id;/*** CreateDate: 2021-4-30 <br/>* Description: 自定义类，用于Users表关联查询Orders表* Version: 1.0**/public class UserOrders extends Users {/*** 订单主键;同时也是订单编号*/private String orderId;/*** 收货人快照*/private String receiverName;/*** 订单总价格*/private Integer totalAmount;/*** 实际支付总价格*/private Integer realPayAmount;public String getOrderId() {return orderId;}public void setOrderId(String orderId) {this.orderId = orderId;}public String getReceiverName() {return receiverName;}public void setReceiverName(String receiverName) {this.receiverName = receiverName;}public Integer getTotalAmount() {return totalAmount;}public void setTotalAmount(Integer totalAmount) {this.totalAmount = totalAmount;}public Integer getRealPayAmount() {return realPayAmount;}public void setRealPayAmount(Integer realPayAmount) {this.realPayAmount = realPayAmount;}}

2、为接口Mapper类添加新的接口方法

这里加了两个，selectAllUsersOrders 和 selectUsersOrders(String userId)

package com.example.demotkmybatisgeneralsecond.mapper;import com.example.demotkmybatisgeneralsecond.pojo.UserOrders;import com.example.demotkmybatisgeneralsecond.pojo.Users;import tk.mybatis.mapper.common.Mapper;import java.util.List;public interface UsersMapper extends Mapper<Users> {List<UserOrders> selectAllUsersOrders();List<UserOrders> selectUsersOrders(String userId);}

3、在对应的*Mapper.xml文件中，添加接口方法对应的Sql实现

a、新建了id为UserOrdersResultMap的ResultMap，继承自BaseResultMap，对应UserOrders类，增加了几个Orders的字段

b、第2步中的每一个新增接口方法，在这里都增加了一个同名id的SQL

<?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.example.demotkmybatisgeneralsecond.mapper.UsersMapper"><resultMap id="BaseResultMap" type="com.example.demotkmybatisgeneralsecond.pojo.Users"><!--WARNING - @mbg.generated--><id column="id" jdbcType="VARCHAR" property="id"/><result column="username" jdbcType="VARCHAR" property="username"/><result column="password" jdbcType="VARCHAR" property="password"/><result column="nickname" jdbcType="VARCHAR" property="nickname"/><result column="realname" jdbcType="VARCHAR" property="realname"/><result column="face" jdbcType="VARCHAR" property="face"/><result column="mobile" jdbcType="VARCHAR" property="mobile"/><result column="email" jdbcType="VARCHAR" property="email"/><result column="sex" jdbcType="INTEGER" property="sex"/><result column="birthday" jdbcType="DATE" property="birthday"/><result column="created_time" jdbcType="TIMESTAMP" property="createdTime"/><result column="updated_time" jdbcType="TIMESTAMP" property="updatedTime"/></resultMap><!--自定义ResultMap--><resultMap id="UserOrdersResultMap" extends="BaseResultMap" type="com.example.demotkmybatisgeneralsecond.pojo.UserOrders"><result column="order_id" jdbcType="VARCHAR" property="orderId"/><result column="receiver_name" jdbcType="VARCHAR" property="receiverName"/><result column="total_amount" jdbcType="INTEGER" property="totalAmount"/><result column="real_pay_amount" jdbcType="INTEGER" property="realPayAmount"/></resultMap><!--自定义SQL--><select id="selectAllUsersOrders" resultMap="UserOrdersResultMap">SELECT a.*, b.id as order_id, b.receiver_name , b.total_amount, b.real_pay_amountFROM users a LEFT JOIN orders b on a.id = b.user_idWHERE b.id is not NULL</select><select id="selectUsersOrders" parameterType="java.lang.String" resultMap="UserOrdersResultMap">SELECT a.*, b.id as order_id, b.receiver_name , b.total_amount, b.real_pay_amountFROM users a LEFT JOIN orders b on a.id = b.user_idWHERE b.id is not NULL AND a.id = #{userId,jdbcType=VARCHAR}</select></mapper>