数据库集合1：user

[{"userId":"zqiang","age":20},
{"userId":"lling","age":27},
{"userId":"wcjing","age":19},
{"userId":"wxia","age":21},
{"userId":"zying","age":18}]

集合2：projects

[{"name":"zqiang","subject":"体育","create-date":"Sat Aug 01 2020 13:45:26 GMT+0800 (中国标准时间)","province":"北京市","city":"北京市","district":"海淀区"},
{"name":"lling","subject":"英语","create-date":"Sat Jul 18 2020 16:45:39 GMT+0800 (中国标准时间)","province":"广东省","city":"广州市","district":"天河区"},
{"name":"wcjing","subject":"数学","create-date":"Fri Aug 09 2019 16:50:52 GMT+0800 (中国标准时间)","province":"辽宁省","city":"沈阳市","district":"铁西区"},
{"name":"lling","subject":"美术","create-date":"Sun Aug 02 2020 16:56:41 GMT+0800 (中国标准时间)","province":"上海市","city":"上海市","district":"徐汇区"},
{"name":"wcjing","subject":"英语","create-date":"Tue Jun 23 2020 17:02:03 GMT+0800 (中国标准时间)","province":"江西省","city":"南昌市","district":"东湖区"},
{"name":"zqiang","subject":"英语","create-date":"Thu Jun 18 2020 18:04:06 GMT+0800 (中国标准时间)","province":"福建省","city":"福州市","district":"台江区"},
{"name":"wxia","subject":"英语","create-date":"Sun Jun 07 2020 22:08:08 GMT+0800 (中国标准时间)","province":"广东省","city":"深圳市","district":"南山区"},
{"name":"zying","subject":"英语","create-date":"Tue Jun 23 2020 13:09:03 GMT+0800 (中国标准时间)","province":"北京市","city":"北京市","district":"丰台区"}]

小程序端通过普通picker和region picker传来几个筛选参数：age,subject,date,region（包含region[0]，region[1]，region[2]）

要求：通过这4个参数查询数据库中的数据，age，subject，date，region传过来的参数等于0，或者region[0]，region[1]，region[2]三个字符串为“全部”时跳过该筛选条件。若参数有效，则分别筛选>age，=subject，

我的程序：

const db = cloud.database()
const _ = db.command
const projects = db.collection("projects")
const $ = _.aggregate
async function getprojectslist (age,date,subject,region){
  //根据date参数判断create-date是全部？1天内？3天内？7天内？
  let mseconds = 0
    if(date == 0){
      mseconds = 0
    }else if(date == 1){
      mseconds = -86400000
    }else if(date == 2){
      mseconds = -259200000
    }else if(date == 3){
      mseconds = -604800000
    }
  let daysel = db.serverDate({offset:mseconds})
  //设置查询条件
  projectsMatch = []
//查询条件为空，返回所有数据
  if((age== 0 && date == 0 && subject == 0 && region == 0) || (age== 0 && date == 0 && subject == 0 && region[0] == "全部" && region[1] == "全部" && region[2] == "全部")){
    const projectList = projects.get().then(res =>{
      return res
    })
    return projectList
  }else{//判断至少存在一个筛选条件，把有用的筛选条件放入数组
    if(date != 0){
      projectsMatch.push($.gte(['$date', daysel]))
    }
    if(trade != 0){
      projectsMatch.push($.eq(['$subject', subject]))
    }
    if(region != 0){
      projectsMatch.push($.eq(['$province', region[0]]))
    }
    if(region != 0 && region[1] != "全部"){
      projectsMatch.push($.eq(['$city', region[1]]))
    }
    if(region != 0 && region[2] != "全部"){
      projectsMatch.push($.eq(['$district', region[2]]))
    }

    const projectList = db.collection('projects').aggregate()
    .lookup({
      from: "user",
      localField: "name",
      foreignField: "userId",
      as: "uid"
    })
    .replaceRoot({//把user集合中的age根据userId和name匹配联表查询放入projects集合中
      newRoot: $.mergeObjects([ $.arrayElemAt(['$uid', 0]), '$$ROOT' ])
    })
    .project({
      uid: 0
    })
    .match(_.expr($.and([
      // $.gte(['$age',Number(age)]),//挨个调试过，单独的功能正常，但多个条件组合就只返回最后一个筛选条件的结果
      $.gte(['$date',daysel]),//单独反复调试，一直无效
      // $.gte(['$subject,subject]),//没有调试过
      // $.eq(['$province',region[0]]),//挨个调试过，单独的功能正常，但多个条件组合就只返回最后一个筛选条件的结果
      // $.eq(['$city',region[1]]),//挨个调试过，单独的功能正常，但多个条件组合就只返回最后一个筛选条件的结果
      // $.eq(['$district',region[2]])//挨个调试过，单独的功能正常，但多个条件组合就只返回最后一个筛选条件的结果
      // projectsMatch//单独调试过，把这个条件数组放在里面无效
    ])))
    .end()
    .then(res => {
      return res
    })
    return projectList
  }
}

请大神帮忙看看问题出在哪儿，感激不尽！！！！！