mongoose静态方法不能识别，各位知道怎么回事吗？

Question

入口文件：

app.set("views engine", "ejs");

app.get("/", function (req, res) {
    router.showStart();
    res.send("zhanshisdf");
});

router.js
var student = require("../model/student.js");
function showStart(req, res) {
    student.hello();
}
exports.showStart = showStart;

mongoose:
var mongoose = require("mongoose");
var db = require("./db.js");
var studentSchema = new mongoose.Schema({
    name: {type: String},
    title: {type: String},
    sex: {type: String},
    age: {type: Number}
});
var studentModel = mongoose.model("student", studentSchema);

studentSchema.statics.hello = function () {
    console.log("hello");
}
module.exports = studentModel;

但是报错：

TypeError: student.hello is not a function
    at Object.showStart (c:\Users\6666\login\controller\router.js:6:13)
    at c:\Users\6666\login\app.js:12:12

你们遇到过这个问题吗，照着官网来做都错啊