突然，猫鼬开始向所有查询返回null

Question

直到昨天，猫鼬仍能正常工作，但是，突然间，我对本地主机的所有查询都返回了null，即使它在MongoDB shell上也是如此。

mongodb config:
const mongoose = require('mongoose')
const fs = require('fs')

async function connect_database() {
    try {
        const promise = mongoose.connect('mongodb://localhost:27017/Amazon_products',
            { useNewUrlParser: true, useUnifiedTopology: true })
        await promise
        console.log("connected to database")
    } catch (error) {
        console.log("database error:" + error)
    }

}
mongoose.Promise = global.Promise
connect_database()

const prods_schema = mongoose.Schema({
    brand: String,
    title: String,
    url: String,
    rating: Number,
    price: Number,
    image: String,
})

const products = mongoose.model('Product_info', prods_schema, 'Product_info')
////query
products.find().exec(
    (res)=>{console.log(res)}

)
//returns null

我试图重新安装mongodb，但没有成功，该怎么办？