Use promise to process MySQL return value in node.js

by

This is gonna be a little scattered, forgive me.

First, assuming this code uses the mysql driver API correctly, here’s one way you could wrap it to work with a native promise:

function getLastRecord(name)
{
    return new Promise(function(resolve, reject) {
        // The Promise constructor should catch any errors thrown on
        // this tick. Alternately, try/catch and reject(err) on catch.
        var connection = getMySQL_connection();

        var query_str =
        "SELECT name, " +
        "FROM records " +   
        "WHERE (name = ?) " +
        "LIMIT 1 ";

        var query_var = [name];

        connection.query(query_str, query_var, function (err, rows, fields) {
            // Call reject on error states,
            // call resolve with results
            if (err) {
                return reject(err);
            }
            resolve(rows);
        });
    });
}

getLastRecord('name_record').then(function(rows) {
    // now you have your rows, you can see if there are <20 of them
}).catch((err) => setImmediate(() => { throw err; })); // Throw async to escape the promise chain

So one thing: You still have callbacks. Callbacks are just functions that you hand to something to call at some point in the future with arguments of its choosing. So the function arguments in xs.map(fn), the (err, result) functions seen in node and the promise result and error handlers are all callbacks. This is somewhat confused by people referring to a specific kind of callback as “callbacks,” the ones of (err, result) used in node core in what’s called “continuation-passing style”, sometimes called “nodebacks” by people that don’t really like them.

For now, at least (async/await is coming eventually), you’re pretty much stuck with callbacks, regardless of whether you adopt promises or not.

Also, I’ll note that promises aren’t immediately, obviously helpful here, as you still have a callback. Promises only really shine when you combine them with Promise.all and promise accumulators a la Array.prototype.reduce. But they do shine sometimes, and they are worth learning.

More Related Contents:

  1. MySQL giving “read ECONNRESET” error after idle time on node.js server
  2. INSERT INTO fails with node-mysql
  3. How can i write in NodeJS with MongoDB the following MySQL Select?
  4. MySQL with Node.js
  5. Preventing SQL injection in Node.js
  6. nodejs mysql Error: Connection lost The server closed the connection
  7. Asynchronous exception handling with bluebird promises
  8. How do I do a bulk insert in mySQL using node.js
  9. Node JS Promise.all and forEach
  10. Node.js can’t authenticate to MySQL 8.0
  11. node.js mysql error: ECONNREFUSED
  12. node.js async/await using with MySQL
  13. Nodejs express and promises not doing what I expect
  14. How to auto generate migrations with Sequelize CLI from Sequelize models?
  15. How to access a RowDataPacket object
  16. using async await and .then together
  17. Retrieve last inserted id with Mysql
  18. Making changes to multiple records based on change of single record with SQL
  19. node.js + mysql connection pooling
  20. connect ECONNREFUSED – node js , sql
  21. Using mongoose promises with async/await
  22. How to make join queries using Sequelize on Node.js
  23. NodeJS MySQL Dump
  24. Node.js connect to MySQL Docker container ECONNREFUSED
  25. NodeJS responded MySQL timezone is different when I fetch directly from MySQL
  26. Javascript Asynchronous Exception Handling with node.js
  27. Error in MySQL library for Node.js
  28. Properly batch nested promises in Node
  29. Which ORM should I use for Node.js and MySQL? [closed]
  30. find number of rows in returned mysql result (nodejs)

Leave a Comment