MongoDB使用聚合平均结果

Question

我有一个文档集合，看起来像这样:

var schema = new Schema({
name: {type: String, required: true},
gradeLevels: {type: String},
subject: {type: String},
standard: {type: String},
description: {type: String},
price: {type: String},
numberOfInternalReviews: {type: Number},
reviews: [{
    content: {type: String},
    rating: {type: Number},
    user: {type: Schema.Types.ObjectId, ref: 'User'},
    userFirstName: {type: String},
    softDelete: {type : Boolean}
}],
averageUserRating: {type: Number}
});

我让他们创建了一个汇总公式，生成每个评论的平均评分，如下所示:

db.applications.aggregate([
      { $unwind: "$reviews" }, 
      { $group: { _id: "$_id", reviews: { $push: "$reviews" },                                       
                 averageUserRating: { $avg: "$reviews.rating" } } }, 
      { $project: { _id: 0, _id: "$_id", reviews: 1, averageUserRating: 1 } }]);

这将根据需要在控制台中生成正确的平均值结果。

我需要做的是将结果推入原始对象的averageUserRating字段。

当我查看应用程序文档时，averageUserRating仍然返回null。

我该怎么做?

Answer 1

也许它是一个type inb项目，所以:修改这个:

{ $project: { _id: 0, _id: "$_id", reviews: 1, averageUserRating: 1 } }]);

:

{ $project: { _id: "$_id", reviews: 1, averageUserRating: 1 } }]);