node.js - MongoServerError:聚合期间的 PlanExecutor 错误::由::'newRoot' 表达式引起，表达式必须计算为对象

Question

如果我尝试从为 mongodb 创建的聚合中获取用户，则会收到错误。

const users = await locations.aggregate([
      {
        $geoNear: {
          near: {
            type: "Point",
            coordinates: [req.query.longitude, req.query.latitude],
          },
          maxDistance: 2000,
          distanceField: "dist.calculated",
          spherical: true,
        },
      },
      {
        $lookup: {
          from: "users",
          localField: "userId",
          foreignField: "_id",
          as: "user",
        },
      },
      {
        $replaceRoot: {
          newRoot: {
            $arrayElemAt: ["$user", 0],
          },
        },
      },
      {
        $project: {
          _id: 1,
          userId: 1,
          name: 1,
          profession: 1,
          hide: 1,
          profilePhotoLink: 1,
          uid: 1,
        },
      },
      {
        $limit: pageSize,
      },
      {
        $skip: pageSize * (req.query.page - 1),
      },
    ]);

它工作正常，我将用户放入数组中，但现在它抛出一个错误。

错误:

code: 500,
  error: 'Server Error',
  api: '/api/users?longitude=77.3720925&latitude=28.6851771&distance=250&page=1',
  level: 'error',
  message: MongoServerError: PlanExecutor error during aggregation :: caused by :: 'newRoot' expression  must evaluate to an object, but resulting value was: MISSING. Type of resulting value: 'missing'. Input document: {_id: 64c4bfc46c4590160ec0e6cc, userId: 64c4bfb66c459012fac0e6c6, location: {coordinates: [180.3721, 21.6852], type: "Point"}, createdAt: 2023-07-29T07:29:08.311Z, updatedAt: 2023-07-29T07:29:08.311Z, __v: 0, dist: {calculated: 2.12997}, user: []}

我不知道为什么失败以及如何解决它？

Answer 1

我猜这是因为对于某些特定的过滤器( longitude=77.3720925&latitude=28.6851771&distance=250 )，数据库中不存在用户，因此在 $lookup 之后有空数组下一步失败并返回 500。

也许您可以简单地使用 $match 进行过滤。没有找到任何用户的点:

const users = await locations.aggregate([
  {
    $geoNear: {
      near: {
        type: "Point",
        coordinates: [req.query.longitude, req.query.latitude],
      },
      maxDistance: 2000,
      distanceField: "dist.calculated",
      spherical: true,
    },
  },
  {
    $lookup: {
      from: "users",
      localField: "userId",
      foreignField: "_id",
      as: "user",
    },
  },
  { 
    $match: { 
      "user.0": {
        "$exists": true 
      }
    }
  },
  {
    $replaceRoot: {
      newRoot: {
        $arrayElemAt: ["$user", 0],
      },
    },
  },
  {
    $project: {
      _id: 1,
      userId: 1,
      name: 1,
      profession: 1,
      hide: 1,
      profilePhotoLink: 1,
      uid: 1,
    },
  },
  {
    $limit: pageSize,
  },
  {
    $skip: pageSize * (req.query.page - 1),
  },
]);