我在 mongodb 中有一個名為 的集合recipe，其中有一個名為 的檔案，comments它是一個陣列，并且在每個配方中都保存了注釋。在comments陣列里面我有一個ratings，它的型別是數字。所以我想計算平均值ratings，但不知道如何使用db.collection().aggregate代碼在配方集合中作業，在帶有評級變數的評論檔案中。
這是recipemongodb中的集合：
const { Double } = require('bson');
const { timeStamp } = require('console');
const mongoose = require('mongoose');
const recipeSchema = new mongoose.Schema({
name: {
type: String,
required: 'This field is required.'
},
description: {
type: String,
required: 'This field is required.'
},
quantity: {
type: Array,
required: 'This field is required.'
},
ingredients: {
type: Array,
required: 'This field is required.'
},
categoryByServing: {
type: String,
enum: ['Reggeli', 'Ebéd', 'Vacsora', 'Desszert', 'Levesek', 'Egyéb'],
required: 'This field is required.'
},
categoryByNationality: {
type: String,
enum: ['Thai', 'Kínai', 'Indiai', 'Olasz', 'Angol', 'Magyar', 'Egyéb'],
required: 'This field is required.'
},
image: {
type: Array,
required: 'This field is required.'
},
comments: [
{
username: String,
comment: String,
date: {
type: Date,
default: Date.now
},
rating: Number
},{
timestamps: true
}
],
count: {
type: Number
},
likes: {
type: Number
},
recipe_id: {
type: String
}
});
recipeSchema.index({ name: 'text', description: 'text' });
const Recipe = module.exports = mongoose.model('Recipe', recipeSchema);這是代碼，我在其中實作了評分平均值計算，它位于評論發布方法中：
/**
* POST /comment-recipe
* Comment Recipe
*/
module.exports.CommentRecipeOnPost = async(req, res) => {
let recipeId = req.params.id
const comment = new Comment({
username: req.body.username,
comment: req.body.comment,
date: req.body.date,
rating: req.body.rating
});
comment.save((err, result) => {
if (err){
console.log(err)
}else {
Recipe.findById(req.params.id, (err, post) =>{
if(err){
console.log(err);
}else{
post.comments.push(result);
post.save();
db.collection('recipes').aggregate([
{
$unwind: "$comments"
},
{
$group: {
_id: null,
avgrating: {
$avg: "$rating"
}
}
}
]).toArray()
.then(results => {
console.log({ rating: results[0].avgrating })
})
.catch(error => console.error(error))
console.log('====comments=====')
console.log(post.comments);
res.redirect('/recipe/' recipeId);
}
})
}
})
}uj5u.com熱心網友回復：
更新
chridam在評論中指出了一種更簡單的方法，僅使用我在第一次演示$project時沒有弄清楚的
db.collection.aggregate([
{
$project: {
_id: 0,
name: 1,
avgRating: {
$avg: "$comments.rating"
}
}
}
])
..或使用$addFieldswhich 將平均評分作為avgRating每個記錄演示的新欄位。如果只需要獲取某些欄位，您可以在之后使用專案步驟
db.collection.aggregate([
{
$addFields: {
avgRating: {
$avg: "$comments.rating"
}
}
}
])
- 您已
$unwind正確完成該步驟，現在您將獲得每條評論的記錄。
{
"_id": "1",
"comments": {
"comment": "commment1-1",
"rating": 4
},
"name": "recipe 1"
},
{
"_id": "1",
"comments": {
"comment": "comment1-2",
"rating": 3
},
"name": "recipe 1"
},
...
- 在
$group舞臺組中，由獨特的東西，如_idor thename和 the$avgshould be of$comments.rating而不是$rating。
In the end the pipeline should look something like this. demo
db.collection.aggregate([
{
$unwind: "$comments"
},
{
$group: {
_id: "$name", //group by something unique for that document containing comments
avgRating: {
$avg: "$comments.rating"
}
}
}
])
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