MongoDB-Aggregate（）然后$ Lookup导致崩溃

Question

我一直在关注tutorial on how to use $Lookup in MongoDB，但是使用该代码时却崩溃了，我不知道为什么（具体错误是“ 404 Not Found”，但是当{{1} }已删除，没有错误）。

这就是我所拥有的：

$Lookup

资产架构

  db.assets.aggregate([{ 
        $lookup: {
                from: "users",
                localField: "currentUser",
                foreignField: "emplyID",
                as: "IDtoNames"
            },

            $project: {
            "assetID": "$assets.assetID",
            "firstName": "$users.name.first",
            "lastName": "$users.name.last",
            "assetType": "$assets.assetType"
            },
        }

用户架构

 var assetSchema = new mongoose.Schema({
assetID: {
    type: Number,
    unique: true
},
assetType: String,
status: String,
currentUser: String,

为什么我使用 var userSchema = new mongoose.Schema({ emplyID: { type: Number, unique: true, required: true }, name: { first: { type: String, required: true }, middle: String, last: { type: String, required: true } 会使应用程序崩溃？