<? 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是命名空间,作用sql语句的隔离,后面还有重要作用 #{}作用就是占位符,相当于jdbc的“?” parameterType:查询的参数类型 resultType:查询结果的数据类型,如果时候pojo应该给全路径。 --> < mapper namespace = "com.wendao.demo.mapper.UserMapper" > < resultMap type = "user" id = "getUserAndOrdersByUserIdMap" > < id column = "userid" property = "id" /> < result column = "username" property = "username" /> < collection property = "orders" ofType = "orders" > < id column = "oid" property = "id" /> < result column = "number" property = "number" /> </ collection > </ resultMap > < select id = "getUserAndOrdersByUserId" resultMap = "getUserAndOrdersByUserIdMap" > select `user`.id userid,`user`.username,orders.id oid,orders.number from `user` LEFT JOIN orders on `user`.id=orders.user_id where `user`.id=#{id} </ select > </ mapper > |