在模式方法内部，“this”在猫鼬 4.4.12 中为空 {}

对象"this"在Schema方法中记录到控制台时是"{}"。这发生在一天前，我一直在阅读教程和其他堆栈溢出问题，但没有找到解决方案。

这是我的模型：

var mongoose    = require("mongoose");
var Schema      = mongoose.Schema;
var constants   = require("../config/constants");
var bcrypt      = require("bcrypt-nodejs");

var UserSchema = new Schema({
    name: String,
    email: String,
    password: String,
    authorization:
    {
        type: Number,
        default: constants.authorization.default
    }
});
UserSchema.pre("save", (next) => {
    var user = this;
    /**
     * Only hash the password when it's been modified or if new.
     */
    // #####################################################
    // ERROR
    // if (!query.isModified("password"))
    //            ^
    // TypeError: query.isModified is not a function
    //
    // user and this == {}
    // ####################################################
    if (!user.isModified("password"))
    {
        return next();
    }
    /**
     * hash password
     */
    bcrypt.hash(user.password, null, null, (err, hash) => {
        if (err)
        {
            return next(err);
        }
        user.password = hash;
        return next();
    });
});
// #####################################################
// ERROR
// user.verifyPassword(req.body.password, match => {
//     ^
// TypeError: user.verifyPassword is not a function
//
// this == {}
// ####################################################
UserSchema.methods.verifyPassword = (reqPassword, callback) => {
    bcrypt.compare(reqPassword, this.password, (err, match) => {
        var e = null;
        var m = match;
        if (err)
        {
            e = err;
            m = false;
        }
        return callback(e, m);
    });
};

module.exports = mongoose.model("User", UserSchema);

这就是我使用它的方式（我已经标记了中断发生的位置）：

//includes express, mongoose, User, constants. this part is ok.
/**
 * Authenticates a user post request
 *
 * @request email string
 * @request password string
 *
 */
router.post("/", (req, res) => {
    /**
     * Retrieve the user
     */
    User.find(
    {
        email: req.body.email
    },
    (err, user) =>
    {
        /**
         * An error occurred
         */
        if (err)
        {
            return res.json({
                success:    false,
                message:    "An mongodb error occurred.",
                error:      err
            });
        }
        /**
         * Check for problems with the email or password.
         */
        if (!user)
        {
            return res.json({
                success:    false,
                message:    "Email or password was incorrect."
            });
        }
        // ##########################################################
        // ERROR
        // user.verifyPassword(req.body.password, match => {
        //     ^
        // TypeError: user.verifyPassword is not a function
        // ##########################################################
        user.verifyPassword(req.body.password, match => {
            if (!match)
            {
                return res.json({
                    success:    false,
                    message:    "Email or password was incorrect."
                });
            }
            /**
             * User authenticated!
             */
            req.session.user = user;
            res.json({
                success: true,
                message: "Successfully authenticated."
            });
        });
    });
});
router.get("/", (req, res, next) => {
    var admin = new User({
        name: "admin",
        email: "admin@admin.net",
        password: "admin",
        authorization: constants.authorization.admin
    });
    // ########################################################
    // ERROR
    // if (!user.isModified("password"))
    //            ^
    // TypeError: user.isModified is not a function
    // #######################################################
    admin.save(function(err) {
        if (err)
        {
            console.log(err);
        }
        console.log('User saved successfully');
        res.json({ success: true });
    });
});

有谁知道这个问题吗？