如何包装 node.js function 以有组织的方式访问它们

Question

So I come to this, I want to write into a DB and do other operations to work with my program logic, this is the guide that I'm following Node.js Class Creation :

//## This is my mysql_test.js file
function MySQL(){
var mysql = require('mysql'); 

var con = mysql.createConnection({
    //data omitted
});


function AppendRecordset (req, res){
    con.connect(function(err) {
      if (err) throw err;
      console.log("Connected!");      
      con.query(req, function (err, res) {
        if (err) throw err;
        console.log("1 record inserted");
      });
    });    
}

function UpdateRecordset (req, res) {
    con.connect(function(err) {
      if (err) throw err;      
      con.query(req, function (err, res) {
        if (err) throw err;
        console.log(result.affectedRows + " record(s) updated");
      });
    });    
}

function DeleteRecordset (req, res){
    con.connect(function(err) {
      if (err) throw err;      
      con.query(req, function (err, res) {
        if (err) throw err;
        console.log("Number of records deleted: " + result.affectedRows);
      });
    });    
}

function GetRecordset (req, res) {
    con.connect(function(err) {
      if (err) throw err;
      con.query(req, function (err, res, fields) {
        if (err) throw err;
        console.log(result);
      });
    });
}
}

I then have in a separate file(s) my app logic, and want to use what of the above as an object/class so I wrote this accordingly to that guide:

//##this is inside my main app file
//declare the sql processor
require('./mysql_test.js');
var DB = MySQL();
DB.AppendRecordset(sql_string, res);  //sql_string contains a valid SQL statement

But when I try to acces it using `` I get this error message: ReferenceError: MySQL is not defined what am I doing wrong?

Answer 1

I think these functions handle your routes, so I didn't change them. Because I don't know how your router is desined.

Create a file dbHangler.js and write this single function:

const mysql = require('mysql'); 

let con;

exports.execQuery = (query) => {
  return new Promise((resolve, reject) => {
    if(!con) {
      con = mysql.createConnection({
        //data omitted
      });
    }
    con.connect(function(err) {
        if(err) {
          reject(err);
        }
        else {
          console.log("Connected!");
          con.query(query, function (err, res) {
            if (err) {
              reject(err);
            }
            else {
              resolve(res);
            }
          });
        }
      });    
  });
};

In your dedicated.js file, now you can write:

const dbObject = require('path/to/dbHandler');

function AppendRecordset (req, res){
    dbObject.execQuery(req)
      .then(result => {
        console.log(result.affectedRows + " record(s) updated");
      })
      .catch(error => {
        // handle error
      });
}

function AppendRecordset (req, res){
    dbObject.execQuery(req)
      .then(result => {
        console.log("Number of records deleted: " + result.affectedRows);
      })
      .catch(error => {
        // handle error
      });
}

function AppendRecordset (req, res){
    dbObject.execQuery(req)
      .then(result => {
        console.log(result);
      })
      .catch(error => {
        // handle error
      });
}

---

UPDATE

I hope this one helps you.

DbHandler.js

const mysql = require('mysql');

class DbHandler {
  constructor(config) {
    let self = this;
    self.dbConfig = config;
    self.connection = mysql.createConnection({
      //data omitted
    });
  }

  queryExecuter(query) {
    let self = this;
    return new Promise((resolve, reject) => {
      self.connection.connect(function (err) {
        if (err) {
          reject(err);
        }
        else {
          console.log("Connected!");
          self.connection.query(query, function (err, res) {
            if (err) {
              reject(err);
            }
            else {
              resolve(res);
            }
          });
        }
      });
    });
  }

  AppendRecordset(query) {
    let self = this;
    return self.queryExecuter(query)
      .then(result => {
        console.log("1 record inserted");
        return result;
      })
      .catch(error => {
        // handle error
        throw error;
      });
  }

  UpdateRecordset(query) {
    let self = this;
    return self.queryExecuter(query)
      .then(result => {
        console.log(result.affectedRows + " record(s) updated");
        return result;
      })
      .catch(error => {
        // handle error
        throw error;
      });
  }

  // and other functions
}

module.exports = DbHandler;

And use it like below:

let DB = require('/path/to/DbHandler');

let myDb = new DB(/* db config */);

db.UpdateRecordset('your query')
  .then(res => {
    console.log(res);
  })
  .catch(err => {
    console.log(err);
  });