mybatis SqlSession

1.在同一个事务中只开启一个sqlSession。

2.在mapper中collection嵌套select只开了一个SqlSession

    <resultMap id="UserOrderIdMap" type="com.zk.domain.User">
        <id property="id" column="id"></id>
        <result property="userName" column="username"></result>
        <collection property="orderIdList"
                    column="{userId=id}"
                    select="selectOrderIdByUserId"/>
    </resultMap>

    <select id="selectUserOrderId" resultMap="UserOrderIdMap">
        select u.id,u.username from t_user u
    </select>

    <select id="selectOrderIdByUserId" resultType="java.lang.Integer">
        select * from t_order where uid=#{userId}
    </select>