How do promises work with asynchronous libraries?

Question

The documentation with promises is horrible. What's the correct way to connect with a database handle, and run something like an express route?

var Promise = require('bluebird');                
var db2 = Promise.promisifyAll(fb);               

var dbh = db2.connectAsync({                       
    host: '127.0.0.1',                            
    database: 'CAFW.FDB',                         
    user: 'SYSDBA',                               
    password: 'pw'                          
  }                                               
);

So now I have dbh, which is a Promise . What do I do with in my routes...

app.get('stuff' function () {
  // How do I use it here?
});


app.get('otherstuff' function () {
  // How do I use it here?
});

Is the right way to do something like...

var db2 = Promise.promisifyAll(fb);

dbh.then( function (dbh) {

   // This is asyncronous code, Express doesn't use promises
   app.get('stuff', function () {
      // And, here I have DBH -- but this is pyramid code again.
      // Do I avoid this pattern? Or, is this required
   };

   app.get('otherstuff', function () {
      // dbh here.
   };

} );

Because if so, that actually lo

Answer 1

First of all, having only one connection shared by the server process horrible, not sure why firebase documentation advocates it. You should use a conncetion pool from which you request a connection for every http request.

If you want to employ the suggested anti-pattern anyway, the way to use it "with promises" is just like they document:

db2.connectAsync({                       
    host: '127.0.0.1',                            
    database: 'CAFW.FDB',                         
    user: 'SYSDBA',                               
    password: 'pw'                          
}).then(function(database) {
    Promise.promisifyAll(database);
    // Their docs have implicit global assignment 
    global.database = database;
});

Again, the usage in express routes is same as they document:

app.get('stuff' function (req, res, next) {
     database.queryAsync("select cast(? as integer) from rdb$database", 123)
        .then(function(result) {

        });
});

I agree the bluebird docs are not that good, 2.0 improves the documentation a lot and adds promisification tutorial, more examples and so on.

---

The transaction example from: https://github.com/hgourvest/node-firebird#using-transaction

would be:

database.startTransactionAsync().bind({})
    .then(function(transaction) {
        // Holy shit this is inefficient, why can't they just expose the classes
        // like every other module
        Promise.promisifyAll(transaction.constructor.prototype);
        this.transaction = transaction;
        return transaction.queryAsync("select cast(? as integer) from rdb$database", 123);
    })
    .then(function(result1) {
        this.result1 = result1;
        return this.transaction.queryAsync("select cast(? as integer) from rdb$database", 456);
    })
    .then(function(result2) {
        this.result2 = result2;
        return this.transaction.commitAsync();
    })
    .then(function() {
        console.log(this.result1[0]);
        console.log(this.result2[0]);
    })
    .catch(function(err) {
        this.transaction.rollback();
        throw err;
    });