在我的資料庫中，每篇文章都有自己的 6 位識別號（除了 id）。每條評論都屬于其中一篇文章。我的問題是，如何在只知道文章編號而不知道文章 id 的情況下查詢評論？
控制器/獲取評論.js：
const Article = require('../models/article')
const User = require('../models/user');
const Comment = require('../models/comment');
module.exports = async function (req, res) {
try {
let { article_number, articleId } = req.body
let filter;
console.log(article_number)
/* Here is my failed attempt: */
if (article_number) filter = { 'article.number': article_number };
if (articleId) filter = { 'article': articleId };
let projection = null
let options = null
let comments = await Comment.find(filter, projection, options).populate('author', 'username fullname').lean()
return res.status(200).send(comments)
} catch (error) {
console.log("error on getting comments: " error.message);
return res.status(500).send('Server side error');
}
}
模型/article.js：
const mongoose = require('mongoose');
const Schema = mongoose.Schema;
const articleSchema = new Schema({
author: { type: Schema.Types.ObjectId, ref: 'User', required: true },
title: { type: String, required: true },
content: { type: String, required: true },
coverPhotoUrl: { type: String, required: false },
number: { type: Number, required: true }, // number is public id for address bar
createdAt: { type: Date, required: true },
category: { type: String, required: false },
fake: { type: Boolean, required: false },
});
module.exports = mongoose.model('Article', articleSchema);
模型/評論.js：
const mongoose = require('mongoose');
const Schema = mongoose.Schema;
const commentSchema = new Schema({
author: { type: Schema.Types.ObjectId, ref: 'User', required: true },
content: { type: String, required: true },
createdAt: { type: Date, required: true },
article: { type: Schema.Types.ObjectId, ref: 'Article', required: true }
});
module.exports = mongoose.model('Comment', commentSchema);
請不要建議做 2 個查詢而不是一個，我已經知道該怎么做。
uj5u.com熱心網友回復：
您可以使用聚合框架并使用$match和$lookup運算子來獲取特定文章編號的評論。以下將是相同的代碼：
db.Article.aggregate( [
{ $match : { number : article_number} },
{
$lookup:
{
from: "Comment",
localField: "_id",
foreignField: "article",
as: "article_comments"
}
}
] )
這將回傳匹配注釋的陣列。
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