Q.ninvoke with node-soap library evaluating function call too early

Question

I am using node-soap to integrate with an external soap-based API. With this library, a client object is created at runtime based on the WSDL. Therefore, the soap client object is not valid at design time. This is a problem trying to use the Q promise library. The Q library is binding/evaluating the method call too early, before it is defined. Here is the code snippet to illustrate.

This is the client code using a promise chain:

innotas.login(user,pass)
.then(innotas.getProjects())
.then(function () {
    console.log('finished');
});

This is the service code snippet for login() which works fine.

this.login = function login (user, password) {
    var deferred = q.defer();

    // some stuff here

    return self.createClient()
    .then(function () {
        self.innotasClient.login({ username: self.innotasUser, password: self.innotasPassword }, function(err, res) {
            if (err) {
              console.log('__Error authenticating to service: ', err);
              deferred.reject(err);
            } else {
              self.innotasSessionId = res.return;
              console.log('Authenticated: ', self.innotasSessionId);
              deferred.resolve();
            }
        });
    });
};

This is the problem. self.innotasClient.findEntity does not exist until after CreateClient()

this.getProjects = function getProjects (request) {

    // initiation and configuration stuff here

    // CALL WEB SERVICE
    self.innotasClient.findEntity(req, function findEntityCallback (err, response) {
      if (err) {
        deferred.reject(err);
      } else {
        deferred.resolve(response);
      }
    })

    return deferred.promise;

    // alternate form using ninvoke
    return q.ninvoke(self.innotasClient, 'findEntity', req).then(function (response) {
        // stuff goes here
    }, function (err) {
        // err stuff goes here
    })
}

This is the runtime error:

        self.innotasClient.findEntity(req, function findEntityCallback (err, r
                           ^
TypeError: Cannot call method 'findEntity' of null
    at getProjects (/Users/brad/Workspaces/BFC/InnotasAPI/innotas.js:147:28)
    at Object.<anonymous> (/Users/brad/Workspaces/BFC/InnotasAPI/app.js:13:15)
    at Module._compile (module.js:456:26)
    at Object.Module._extensions..js (module.js:474:10)

This code works fine with callbacks. Any idea how to get this to work with the promise library?

Answer 1

The Q library is binding/evaluating the method call too early, before it is defined

No - you are:

innotas.login(user,pass)
.then(innotas.getProjects())

Here you're calling getProject() before passing its results into the then method. However, then does expect a callback function, which will be called when the promise if resolved. You'd use

innotas.login(user,pass).then(function(loginresult) {
    innotas.getProjects()
})

If the client does not exist until the createClient method yields, the client should be the result of that function - let it return a promise for the client!

Your lib should then look like this:

this.login = function login (user, password) {
    // some stuff here
    return self.createClient().then(function(client) {
        return Q.ninvoke(client, "login", {
            username: self.innotasUser,
            password: self.innotasPassword
        }).then(function(res) {
            self.innotasSessionId = res.return;
            console.log('Authenticated: ', self.innotasSessionId);
            return client;
        }, function(err) {
            console.log('__Error authenticating to service: ', err);
            throw err;
        });
    });
};
this.getProjects = function getProjects (client) {
    // initiation and configuration stuff here

    // CALL WEB SERVICE
    return q.ninvoke(client, 'findEntity', req).then(function (response) {
        // stuff goes here
    }, function (err) {
        // err stuff goes here
    });
};