无法访问其他模块中的mysql.Connection对象

尝试从不同的文件创建mysql模型时出错。基本上，我在server.js中创建了连接对象并将其导出。我正在尝试从models/product.js访问连接对象。你能检查一下下面的代码并告诉我出了什么问题吗。 我有/server.js，如下所示：

    const http = require('http');
    const app = require('./app.js');
    http.createServer(app).listen(3000);
    
    //DB connection
    
    const mysql = require('mysql');
    
    const con = mysql.createConnection({
        host : "XXXXXXX",
        user : "******",
        password: "*******",
        database: "********"
    });
    
    con.connect(function(err){
        if(err){
        console.log("Not connected!!!")
        //console.log(err);
        }
        else{
            console.log("Sql server connected");
        };
    });
    
    console.log(con);
    
    module.exports = con;
    
    and /api/models/products.js
    
    
const conn = require('../../server.js');
console.log(conn + "Models");

sql = "CREATE TABLE animals (id MEDIUMINT NOT NULL AUTO_INCREMENT,name CHAR(30) NOT NULL,PRIMARY KEY (id));";

conn.connect(function(err) {
    if (err) throw err;
    console.log("Connected!");
    var sql = "CREATE TABLE customers (name VARCHAR(255), address VARCHAR(255))";
    conn.query(sql, function (err, result) {
      if (err) throw err;
      console.log("Table created");
    });
  });

和/api/app.js作为

const express = require('express');
const app = express();
const morgan = require('morgan');
const cors = require('cors');
const productRoutes = require('./api/routes/products.js');
const orderRoutes = require('./api/routes/orders.js');



app.use(morgan('dev'));
app.use(cors());
app.use('/products', productRoutes);
app.use('/orders', orderRoutes);

//error handling for undefined routes
app.use( function (req, res){
    res.writeHead('404');
    res.write('Resource not found or you are not authorized');
    res.end();
});

module.exports = app;

和/api/models/products.js

const conn = require('../../server.js');
console.log(conn + "Models");

sql = "CREATE TABLE animals (id MEDIUMINT NOT NULL AUTO_INCREMENT,name CHAR(30) NOT NULL,PRIMARY KEY (id));";

conn.connect(function(err) {
    if (err) throw err;
    console.log("Connected!");
    var sql = "CREATE TABLE customers (name VARCHAR(255), address VARCHAR(255))";
    conn.query(sql, function (err, result) {
      if (err) throw err;
      console.log("Table created");
    });
  });

当尝试在models/products.js中控制台.log（conn）时，我得到一个空对象，conn.connect也失败了