静态方法内执行MongoDB查询导致程序无限等待问题排查

我跟着教程开发登录与授权系统，当前卡在Schema静态方法调用数据库操作的环节：

• 在静态方法内调用this.findOne({})时程序进入无限等待，控制台仅输出"Static Method Triggered"，后续代码无法执行
• 移除查询语句后，程序又会在this.create行无限等待，console.log(this)返回空对象{}
• 其他数据库查询功能正常

模型代码如下：

const mongoose = require('mongoose')
const Schema = mongoose.Schema
const bcrypt = require('bcrypt')

const userSchema = new Schema({
    email: {
        type: String,
        required: true,
        unique: true,
    },
    password: {
        type: String,
        required: true
    }
})
userSchema.statics.signup = async (email, password) => {
    console.log("Static Method Triggered")
    const exists = await this.findOne({ email })
    console.log("Verifying existence")

    if (exists) {
        throw Error("Email is already in use")
    }
    console.log("Existence verified")

    const salt = await bcrypt.genSalt(5)
    const hash = await bcrypt.hash(password, salt)
    console.log(hash)
    const user = await this.create({ email: email, password: hash })
    console.log("End of function")
    return user
}

module.exports = mongoose.model('User', userSchema) 

原因分析 #

问题核心是箭头函数的this绑定规则：Mongoose的静态方法需要this指向模型本身，但箭头函数不会绑定自己的this，它会继承外层作用域的this（此处为空对象）。所以调用this.findOne、this.create时，实际上是在空对象上调用不存在的方法，导致await永远无法得到结果，进入无限等待。

解决方案 #

将静态方法的箭头函数改为普通函数，让this正确绑定到User模型：

userSchema.statics.signup = async function(email, password) {
    console.log("Static Method Triggered")
    const exists = await this.findOne({ email })
    console.log("Verifying existence")

    if (exists) {
        throw Error("Email is already in use")
    }
    console.log("Existence verified")

    const salt = await bcrypt.genSalt(5)
    const hash = await bcrypt.hash(password, salt)
    console.log(hash)
    const user = await this.create({ email: email, password: hash })
    console.log("End of function")
    return user
}

内容的提问来源于stack exchange，提问作者hamza malik