Develop Reference

How to query a database from an Azure function in js

I have an IOT hub getting some data. I also have an Azure function app in js that is triggered when an IOT event occurs. In the function app, I want to query the incoming data against a azure sql database.
In the azure function->application settings->connection string, I created a connection string x with value of the azure db connection string. My index.js file is as below.
module.exports = function (context, IoTHubMessages) {
context.log(`JavaScript eventhub trigger function called for message array ${IoTHubMessages}`);
IoTHubMessages.forEach(message => {
context.log(`Processed message ${message}`);
var sqlConnection = x;
});
context.done();
};
I get an error that x is not defined. How can I access x? Also how how to execute a select query from here.
Any help will be greatly appreciated.

Try accessing your app setting using process.env["x"] Here are the docs, and here's a related issue you may face if you're trying to run this locally.
I don't have experience writing Javascript functions to execute a select query, but this documentation seems like a good place to start: Use Node.js to query Azure SQL Database

There is no easy way to access connection strings in Node.js.
Instead, the suggestion is to use app settings for all your secrets and connection strings. You can them access them using process.env.YourAppSetting.
See similar questions one and two.

Meteor: How can I get useraccounts package to write a new user doc into a remote collection?

I'm using the packages accounts-password and useraccounts:bootstrap and it all works fine, meaning the sign-on form creates a new doc in the Meteor.users collection. But I don't want any collection on the client facing app, hence I do have a second app running to which I successfully connect via DDP.connect() and I can exchange all necessary docs/collections via pub/sub and calling methods on the remote app.
The only thing that doesn't work is the useraccount doc. I've used (on the client app):
remote.subscribe('users', Meteor.userId(), function() {
});
and (on the remote app):
Meteor.publish('users', function() {
return Meteor.users.find({});
});
even though I'm not sure if there is a pub/sub already included in the package. Still, the doc is written to the local (client) app and not to the remote app.
How can I achieve this?

useraccounts:core simply makes use of Accounts.createUser on the server side (see this line) within a method called from the client-side (see this another line).
So the new user object is created from the server side and not from the client (though it flows all the way down to the client thanks to the DDP and default users subscriptions...).
If you're really looking to change the defaul behaviour provided by the Meteor core Accounts packages (accounts-base, accounts-password in this case...) you should try to override the Accounts.createUser method which is were all begins...
In any case be warned that the current user is published to the client by default: see these lines
Finally, to prevent useraccounts:core to use the Accounts API you could try to override the AtCreateUserServer method and deal with the creation of a new user on a remote application inside there.

Package accounts-base provide such functionality.
The accounts-base package exports two constructors, called AccountsClient and AccountsServer, which are used to create the Accounts object that is available on the client and the server, respectively.
Nevertheless, these two constructors can be instantiated more than once, to create multiple independent connections between different accounts servers and their clients, in more complicated authentication situations.
Documentation: Accounts (multi-server)

node.js - how to push an address change to a client?

I am trying to set up a simple presentation using three computers synchronized by a central server, and I figured node would be the ideal tool.
I was wondering if there's any way to have all three computers connect to the server via the browser, and if I could control the server to push changes to each?
For example:
Computer-1 visits 10.0.0.1?comp=1?slide=1
Computer-2 visits 10.0.0.1?comp=2?slide=1
Computer-3 visits 10.0.0.1?comp=3?slide=1
Then from the server commandline, I would like to be able to trigger a change so the clients will each be redirected accordingly like so:
Computer-1 visits 10.0.0.1?comp=1?slide=2
Computer-2 visits 10.0.0.1?comp=2?slide=2
Computer-3 visits 10.0.0.1?comp=3?slide=2
I'm new to node, so I'm not even sure if this is the ideal platform, but was wondering what terminology I should be researching to be able to build something like this?

Thank you for your responses, I ended up looking into socket.io and managed to write this system in one evening! Node + socket.io and express is a pretty amazing tool with the socket emit events.
Thank you for pointing me in the right direction, this is exactly the tool I was looking for.
Just in case it may help anyone, in my client/jade template, I have something like:
socket.on('slideUpdate', function (data) {
// Do things with the data
}
and on the server app.js:
io.on('connection', function (socket) {
socket.on('slideChange', function (data) {
// logic for setting slide data
io.sockets.emit('slideUpdate', { example: exampleData ... });
});
});
where a slideChange event is triggered via a button on the client-side template.

For such a presentation I would use the most simple solution, i.e. not websockets, not server-sent events and not long-polling.
Just do a short poll, i.e. every client calls the server every 100ms for updates. The server then responds with a status update (if there is one).

Make Parse Data Modification Only Accessible from the Cloud

I am trying to create an app on Parse. That app uses data, but in order to make the data storage more secure, you would not like the clients to be able to run it. Instead, only the server should be able to modify data,
So far, I haven't seen any options as to how to achieve that, except by using user/role-based authentication, and that is something I'd rather avoid because it is the environment, not the user or role I would like to make the data access depend on.
Are there any ways to do that?

Turn off write access for everyone on each class, then in your Cloud Code use the master key which lets you bypass permissions.

You could use a beforeSave handler in Cloud Code...
Parse.Cloud.beforeSave('myClassName', function(req, res) {
if (req.master) {
res.success();
} else {
res.error('Cannot change this data.');
}
}
Then only requests made using the Master Key can alter this data.
In other places in Cloud Code, you can pass this option for individual requests like this:
obj.save(null, { useMasterKey: true });
Or turn it on for actions that follow:
Parse.Cloud.useMasterKey();

Multiple Websockets

I'm trying to use two websockets on one page. This is my code:
var pageViewWs = new WebSocket("ws://localhost:9002/pageView");
var sessionWs = new WebSocket("ws://localhost:9002/session");
pageViewWs.onmessage = function (event) {
alert("PageView");
};
sessionWs.onmessage = function (event) {
alert("Session");
};
Only the PageView alert appears. On the server side no requests are made to /session, only to /pageView.
Now, if I switch var pageViewWs and var sessionWs around then the Session alert is shown instead of the PageView. It is not because they are alerts, I've tried appending to the body and to divs and I've stepped through using Firebug. It seems that only one WebSocket can be created at a time although in Firebug the properties for pageViewWs and sessionWs appear the same with the exception of their url.
I've only tested this in Firefox 15.0.1. Is there some sort of Websocket limitation whereby you can only run one at a time? Or is something wrong with my code?

I faced the same problem to run multiple services through the same port. So, I created a PHP library to do this.
Why ?
Some free plans of hosting providers don't allow you to bind to ports or allow you to bind to one port. In case of OpenShift Cloud Server, you can only bind to port 8080. So, running multiple WebSocket services is not possible. In this case, Francium DiffSocket is useful.
You can run different services on the same port using a PHP library called Francium DiffSocket.
After setting up Francium DiffSocket, you can do this for using different services :
var chatWS = new WebSocket("ws://ws.example.com:8000/?service=chat");
var gameWS = new WebSocket("ws://ws.example.com:8000/?service=game");
An example are these services which are running through a single port :
Finding Value Of Pi
Advanced Live Group Chat With PHP, jQuery & WebSocket
Live Group Chat With PHP, jQuery & WebSocket

I believe you can only create one WebSocket connection from a client to a specific port on the host. Have you tried either running the two services on different ports, or on different servers? This would allow you to determine the limitation...

Apart from the HTTP Request head both the request are the same. They hit the same application server on the same port. It is up to the server side application to treat each connection differently based on the HTTP request that initiated it.
I've done this in node. You could do it manually but packages like
espress-ws
or express-ws-routes
eases the process.