Pick up connection if there is a disconnect - sql-server

Question

I make use of this specific version: https://github.com/patriksimek/node-mssql/tree/v3.3.0#multiple-connections of the SQL Server npm package.
I have been looking through the documentation of tedious (the underlying lib) and Microsofts documentation (see the github link above).
I couldn't find anything that does something simple like getCurrentConnection, or getConnectionStatus or anything similar.
I had two ways to solve this problem but I'm not happy with both of them so that's why I'm asking here.
My first approach was to set a timeout and let the connect function call itself on each catch(err).
The second one was to handle this in the middleware but then if all is working fine it will make a connection to SQL on every request and closing that connection again.
My middleware function:
api.use(function(err, req, res, next){
sql.close();
sql.connect(config.database).then(() => {
next();
}).catch(function(err) {
sql.close();
server.main();
});
});
I want to, if possible pick up the connection instead of closing and starting a new one with regards to when the server or the database crashes I still have some data from the existing function.

Answer 1

By the help of Arnold I got to understand the mssql package and it's inner workings a lot better.
Therefor I came up with the following solution to my problem.
let intervalFunction;
const INTERVAL_DURATION = 4000;
if (require.main === module){
console.log("Listening on http://localhost:" + config.port + " ...");
app.listen(config.port);
// try to connect to db and fire main on succes.
intervalFunction = setInterval(()=> getConnection(), INTERVAL_DURATION);
}
function getConnection() {
sql.close();
sql.connect(config.database).then(() => {
sql.close();
clearInterval(intervalFunction);
main();
}).catch(function(err) {
console.error(err);
console.log(`DB connection will be tried again in ${INTERVAL_DURATION}ms`)
sql.close();
});
}
Once the initial connection has been made but it got lost in the meantime the pool will pick up the connection automatically and handle your connections

Answer 2

If I understood you correctly, you basically want to reuse connections. Tedious has built-in connection pooling, so you don't have to worry about re-using them:
var config = {
user: '...',
password: '...',
server: 'localhost',
database: '...',
pool: {
max: 10,
min: 0,
idleTimeoutMillis: 30000
}
}
In the example above (just copied from the GitHub URL you've posted), there will be 10 connections in the pool ready to use. Here's the beauty: the pool manager will handle all connection use and re-use for you, i.e., the number of connections are elastic based on your app's needs.
As you've mentioned, what about DB crashes? That too is built-in: connection health-check:
Internally, each Connection instance is a separate pool of TDS
connections. Once you create a new Request/Transaction/Prepared
Statement, a new TDS connection is acquired from the pool and reserved
for desired action. Once the action is complete, connection is
released back to the pool. Connection health check is built-in so once
the dead connection is discovered, it is immediately replaced with a
new one.
I hope this helps!