带有正则表达式的猫鼬聚合不起作用

Question

我想使用从用户集合中提交的用户名过滤事件，但不知何故使用正则表达式聚合无法返回零项。但对于描述、事件名称等其他字段，它工作正常。我错过了什么？

我的代码如下：

  if (requestedData.searchtext)
  {
    eventsFilterJson = {...eventsFilterJson, $or: [
      { user_name: { $regex: requestedData.searchtext, $options: "i" } },
      ]}
  }

  Event.aggregate([
    {
        $geoNear: {
          near: point,
          //maxDistance: maxDistance,
          minDistance: last_distance,
          key: locKey,
          distanceField: "distance",
          spherical: true,
          distanceMultiplier: 1 / distanceMultiplier,
          query: eventsFilterJson,
          num:20
        }
    },
    {
      $lookup: {
        from: "users",
        let: { userId: '$$ROOT.user_id' },
        pipeline: [
          {
            $match: {
              $expr: { $eq: ["$_id", "$$userId"] }
            }
          },
          {
            $project:{
              full_name:"$full_name"
            }
          }
        ],
        as: "event.user"
      }
    },
    { $unwind: { path: "$event.user", preserveNullAndEmptyArrays: true } },

    {
      $project: {
        user_name: {
            $ifNull: ["$event.user.full_name", '']
          },
      }
    } 
  ])
  .exec((err, results) => {
      if (err) {        
        res.json(appfunctions.failResponse("msg_something_wrong"));
      } else {
        res.json(appfunctions.successResponse("msg_filter", results, req.user));
      }
    });