Understanding JS callbacks w/ Azure Functions & Tedious SQL

问题

The following code is for an Azure Function (Serverless) Http endpoint. The code uses the Tedious NPM package for connecting to an Azure SQL database.

The challenge I am having, is understanding how to properly return the results from the callback behavior prior to the function exiting. Ideally, I'd like to do all my SQL work done synchronously in-line, without the callback behavior, but I understand that may not be best practice.

Can anyone explain how this code could be modified to better demonstrate the right way to return the SQL/Tedious callback results so they are delivered to the JSON output?

const { Connection, Request } = require('tedious');
require('dotenv').config();

module.exports = async function (context, req) {
  try {
    const config = { /* redacted for brevity */ };
    let connection = new Connection(config);
    connection.on('connect', function (err) {
      if (err) {
        context.log('Error: ', err);
      }
      const request = new Request(
        `SELECT TOP 10 Id, Username FROM Users`,
        (err, rowCount, rows) => {
          if (err) {
            console.error(err.message);
          } else {
            console.log(`${rowCount} row(s) returned`);
            // this object does not render in output (called after context.log outside callback)
            context.res.status(200).json({ data: 'ok' });
          }
        }
      );
      connection.execSql(request);
    });

    // This line is hit before the callback is called
    //   There is no response sent back to the browser
    context.log('Hey, I ran before the callback...');
  } catch (error) {
    context.log('error occurred ', error);
    context.res.status(500).send(error);
  }
};

Update Should anyone else stumble upon this post, I switched to using the 'mssql' node package, and this works as expected for me. Note the connectionstring has to have ?encrypt=true per the package documentation.

I would still like to know what was wrong with the original code if possible.

const sql = require('mssql');
require('dotenv').config();

module.exports = async function (context, req) {
  try {
    await sql.connect(process.env.AZURE_SQL_CONNECTIONSTRING);
    const result = await sql.query`select Id, Username from Users`;
    context.res.status(200).send(result);
  } catch (error) {
    context.log('error occurred ', error);
    context.res.status(500).send(error);
  }
};

来源：https://stackoverflow.com/questions/62233383/understanding-js-callbacks-w-azure-functions-tedious-sql

标签

node.js

sql-server

azure

tedious