SELECT在node.js中不起作用

Question

I'm trying to use a SELECT query on my SQL database using node.js, the SELECT query below should work but doesn't. This is weird because I think this should work but it doesn't even enter the client.query function. I also copied my INSERT query which is actually working to show you my connection to the database works fine.

What am I doing wrong in the SELECT query?

CreateConnection

var mysql = require('mysql');
var client = mysql.createConnection({
    host: '***',
    user: '***',
    password: '***',
    database: '***'
});

SELECT Query (Not working)

    function query(sql){
      var returnvalue = "tempVal";
      client.connect();
      client.query('SELECT 1 + 1 AS solution', function(err, rows, fields) {
        returnvalue = "doens't even enter function";
        if (err) throw err;

        returnvalue = rows[0].solution;
      });
      client.end();    
      return returnvalue;
    }

INSERT Query (Is working)

function query(sql){
  client.connect();
  client.query('INSERT INTO users (username) VALUES("foo")');
  client.end();
}

Answer 1

As .query() is an asynchronous method, you won't be able to return the value as the callback will be called after the return is evaluated.

You'll have to continue the callback pattern:

function query(sql, callback) {
    client.connect();
    client.query(sql, function (err, rows, fields) {
        if (err) {
            callback(err);
        else
            callback(null, rows, fields);
    });

    client.end();
}

Correction: Seems client.end() will allow current queries to finish before the connection actually closes.

Closing the connection is done using end() which makes sure all remaining queries are executed before sending a quit packet to the mysql server.

Though, calling .end() inside the callback is commonplace for many APIs as they will cut-off any pending actions.