Mybatis关联查询对象嵌套

public class WeixinActivity2018User  implements Serializable{

    /** serialVersionUID*/
    private static final long serialVersionUID = -2740162776768956231L;

    private int id;
    private String nickname;  //昵称
    private String headurl;   //头像
    private String openid;    //微信用户OpenId
    private String unionid;
    private String phone;     //用户手机号
    private int count;        //积攒数
    private String createtime;//创建时间
    private String uptime;    //更新时间
    private List<WeixinActivity2018UserAssist> activity2018UserAssists;//点赞用户信息

public class WeixinActivity2018UserAssist  implements Serializable{

    /** serialVersionUID*/
    private static final long serialVersionUID = -2740162776768956232L;

    private int aid;
    private int uid;
    private String nickname;
    private String headurl;
    private String openid;
    private String unionid;
    private String createtime;

  <resultMap id="BaseResultMap" type="com.lh.wx.model.WeixinActivity2018User">
    <id column="id" jdbcType="INTEGER" property="id" />
    <result column="openid" jdbcType="VARCHAR" property="openid" />
    <result column="unionid" jdbcType="VARCHAR" property="unionid" />
    <result column="phone" jdbcType="VARCHAR" property="phone" />
    <result column="nickname" jdbcType="VARCHAR" property="nickname" />
    <result column="headurl" jdbcType="VARCHAR" property="headurl" />
    <result column="count" jdbcType="INTEGER" property="count" />
    <result column="createtime" jdbcType="DATE" property="createtime" />
    <result column="uptime" jdbcType="DATE" property="uptime" />
    <collection  property="activity2018UserAssists"  ofType="com.lh.wx.model.WeixinActivity2018UserAssist">
            <id property="aid" column="aid" />
             <result column="uid" jdbcType="INTEGER" property="uid" />
            <result column="aopenid" jdbcType="VARCHAR" property="openid" />
            <result column="aunionid" jdbcType="VARCHAR" property="unionid" />
            <result column="anickname" jdbcType="VARCHAR" property="nickname" />
            <result column="aheadurl" jdbcType="VARCHAR" property="headurl" />
            <result column="acreatetime" jdbcType="DATE" property="createtime" />
    </collection>
  </resultMap>
  <sql id="Base_Column_List">
    openid,unionid,phone,nickname,headurl,count,createtime,uptime
  </sql>
  <insert id="insertActivity2018User"  useGeneratedKeys="true" keyProperty="id" parameterType="com.lh.wx.model.WeixinActivity2018User" >
    insert into t_weixin_activity_2018_user (openid,unionid,phone,nickname,headurl,createtime,uptime)
    values (
        #{openid,jdbcType=VARCHAR},#{unionid,jdbcType=VARCHAR},#{phone,jdbcType=VARCHAR}, #{nickname,jdbcType=VARCHAR}, #{headurl,jdbcType=VARCHAR},now(),now()
    )
  </insert>
    <select id="selectTalCount" resultType="java.lang.Integer"  parameterType="java.util.Map">
        SELECT  count(twau.id)
        from  t_weixin_activity_2018_user twau
        <if test="openid != '' and openid != null">
            and twau.openid = #{openid}
        </if>
        <if test="id != 0 and id != null">
            and twau.id = #{id}
        </if>
        <if test="phone != '' and phone != null">
            and twau.phone = #{phone}
        </if>
    </select>
    <select id="queryActivity2018User" parameterType="java.util.Map" resultMap="BaseResultMap" >
        SELECT 
         twau.id,twau.openid, twau.unionid, twau.phone, twau.nickname, twau.headurl, twau.count,date_format( twau.createtime, '%Y-%m-%d %H:%m:%s') as createtime,date_format( twau.uptime, '%Y-%m-%d %H:%m:%s') as uptime
        ,twaua.aid,twaua.uid,twaua.openid as aopenid,twaua.unionid as aunionid,twaua.nickname as anickname,twaua.headurl as aheadurl,date_format(twaua.createtime, '%Y-%m-%d %H:%m:%s') as acreatetime ,
        twaua.phone as aphone
        from  t_weixin_activity_2018_user twau LEFT  JOIN t_weixin_activity_2018_user_assist twaua on twau.id=twaua.uid  where 1=1
        <if test="openid != '' and openid != null">
            and twau.openid = #{openid}
        </if>
        <if test="id != 0 and id != null">
            and twau.id = #{id}
        </if>
        <if test="phone != '' and phone != null">
            and twau.phone = #{phone}
        </if>
        <if test="start != '' and start != null  and start != 0">
            order by tlb.createtime desc limit ${start}, ${number}
        </if>
  </select>