如何从 NodeJS 中的 SQL 服务器获取列表记录

Question

I start to develop a simple web application with NodeJS. and when I try to get a list record from SQL Server to show on the list page but somehow it's not working.

Here is the code:

const express = require("express");
const bodyParser = require("body-parser");
const sql = require("mssql");
const DBUtils = require("./DBUtils");

const app = express();

app.get("/all", (req, res, next) => {
  let mypromise = new Promise((reso, rej) => {
    let nameList = DBUtils.getNameList(sql);
    if (nameList !== null || typeof nameList !== "undefined") {
      reso(nameList);
    } else {
      rej("Error");
    }
  })
    .then((result) => {
      res.send(result);
    })
    .catch((err) => {
      console.log(err);
    });
});

app.get("/", (req, res, next) => {
  console.log("the / route");
  res.send("<h1>Hello to NodeJS</h1>");
});

app.listen(5003);

My DBUtils

const config = {
  user: "sa",
  password: "123",
  server: "DESKTOP-7KGJI7L", // You can use 'localhost\\instance' to connect to named instance
  database: "java",
  options: {
    encrypt: false,
  },
};

const getNameList = (sql) => {
  let nameList = "";
  let errorString = "";
  // Create connection
  sql.connect(config, function (err) {
    // Err
    if (err) {
      console.log(err);
    }

    // Create Request object
    let sqlRequest = new sql.Request();

    // QueryString
    let queryString = `select * from NAME`;
    // Run the query
    sqlRequest.query(queryString, (err, data) => {
      if (err) console.log(err);

      //console.log(data); //data.recordset(array)[index].name
      data.recordset.forEach((el) => {
        nameList += `<li>${el.name}</li>`;
      });
      return nameList;
    });
  });
};

exports.getNameList = getNameList;

I pretty sure something wrong in Promise line but don't know how to fix it. Any suggest?

Answer 1

I think you are a newbie in Nodejs You made a common mistake. You did not use promise pattern correctly. Also, no need to pass next callback unless required.

Change getNameList as below:

const getNameList = (sql) => {
  let nameList = "";
  let errorString = "";
  // Create connection
  return new Promise (function(resolve,reject) {
  sql.connect(config, function (err) {
    // Err
    if (err) {
      console.log(err);
       reject(err)
    }

    // Create Request object
    let sqlRequest = new sql.Request();

    // QueryString
    let queryString = `select * from NAME`;
    // Run the query
    sqlRequest.query(queryString, (err, data) => {
      if (err) {console.log(err)
         reject(err)
       }
      //console.log(data); //data.recordset(array)[index].name
      data.recordset.forEach((el) => {
        nameList += `<li>${el.name}</li>`;
      });
      resolve(nameList);
     });
    });
  })
};

Change app.get("/all") as below:

 app.get("/all", (req, res) => {
        DBUtils.getNameList(sql).then(function(list) {
            res.status(200).send(list)
        }).catch(function(err) { //handle error here
         res.status(500)
        })
    })

• Moreover, learn how to use promises and async-await.
• Use appropriate body-parser as per requirement ie json , text etc.
• Learn how and when to use next