Mybatis嵌套查询与嵌套结果

一对多关系：一是用户，多是订单

实体类User

public class User {private Integer id;private String name;private Integer age;private List<UserOrder> orders;}

实体类UserOrder

public class UserOrder {private Integer id;private String name;private Integer userId; }

使用嵌套结果来查询：相当于使用一条sql语句关联多张表查询出所有结果，然后根据映射给订单类属性赋值

<!--1.嵌套结果--> <select id="selectUser" resultMap="selectUser1">select u.id,u.name,u.age,o.id as order_id,o.name as order_name from t_p_user u left join t_p_user_order oon u.id = o.user_id and u.id = #{id}</select><resultMap id="selectUser1" type="com.seakoon.model.User"><id column="id" property="id" /><result column="name" property="name"/><result column="age" property="age"/><collection property="orders" ofType="com.seakoon.model.UserOrder" column="id"><id column="order_id" property="id" /><result column="order_name" property="name" /><result column="id" property="userId" /></collection></resultMap>

使用嵌套查询：查询订单数据时新用一条sql来查。参数是column属性的值，如果多参数的话：使用
column=“{property1 = column1,property2 = column2…}”

<!--2.嵌套查询--><select id="selectUserNew" resultMap="selectUser2">select id,name,age from t_p_user where id = #{id}</select><resultMap id="selectUser2" type="com.seakoon.model.User"><id column="id" property="id" /><result column="name" property="name"/><result column="age" property="age"/><collection property="orders" ofType="com.seakoon.model.UserOrder" column="id" javaType="java.util.ArrayList"select="selectOrderById"><id column="order_id" property="id" /><result column="order_name" property="name" /><result column="id" property="userId" /></collection></resultMap><select id="selectOrderById" resultType="com.seakoon.model.UserOrder">select id,name,user_id as userId from t_p_user_order where user_id = #{id}</select>

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