I currently have a Node.JS server set up that is able to read and write data from a FireBase database when a request is made from a user.
I would like to implement time based events that result in an action being performed at a certain date or time. The key thing here though, is that I want to have the freedom to do this in seconds (for example, write a message to console after 30 seconds have passed, or on Friday the 13th at 11:30am).
A way to do this would be to store the date/time an action needs be performed in the database, and read from the database every second and compare the current date/time with events stored so we know if an action needs to be performed at this moment. As you can imagine though, this would be a lot of unnecessary calls to the database and really feels like a poor way to implement this system.
Is there a way I can stay synced with the database without having to call every second? Perhaps I could then store a version of the events table locally and update this when a change is made to the database? Would that be a better idea? Is there another solution I am missing?
Any advice would be greatly appreciated, thanks!
EDIT:
How I currently initialise the database:
firebase.initializeApp(firebaseConfig);
var database = firebase.database();
How I then get data from the database:
await database.ref('/').once('value', function(snapshot){
snapshot.forEach(function(childSnapshot){
if(childSnapshot.key === userName){
userPreferences = childSnapshot.val().UserPreferences;
}
})
});
The Firebase once() API reads the data from the database once, and then stops observing it.
If you instead us the on() API, it will continue observing the database after getting the initial value - and call your code whenever the database changes.
It sounds like you're looking to develop an application for scheduling. If that's the case you should check out node-schedule.
Node Schedule is a flexible cron-like and not-cron-like job scheduler
for Node.js. It allows you to schedule jobs (arbitrary functions) for
execution at specific dates, with optional recurrence rules. It only
uses a single timer at any given time (rather than reevaluating
upcoming jobs every second/minute).
You then can use the database to keep a "state" of the application so on start-up of the application you read all the upcoming jobs that will be expected and load them into node-schedule and let node-schedule do the rest.
The Google Cloud solution for scheduling a single item of future work is Cloud Tasks. Firebase is part of Google Cloud, so this is the most natural product to use. You can use this to avoid polling the database by simply specifying exactly when some Cloud Function should run to do the work you want.
I've written a blog post that demonstrates how to set up a Cloud Task to call a Cloud Functions to delete a document in Firestore with an exact TTL.
When we are working in firebase using javascript which event is triggered after we insert data using ref.push or ref.set.
I wanted to know if my data is inserted or not
I also wanted to throw an error when user have disconnected from internet while inserting data in firebase
I haven't seen any function or any method in internet which tells me about if data is successfully inserted or not.
This functions Promise-based, so you can use try/catch:
try {
firebase.push(data) // or set
} catch (error) {
console.log(error) // here is error
}
The Firebase Realtime Database doesn't consider a lack of internet connection an error condition. Instead it continues to work to its best ability in the given conditions.
When you perform a write operation (with set, push, update, or remove) while there is no internet connectivity:
The first client fires local events immediately, so that your app can update the UI for the new/updated data.
It then queues the write operation for delivery once the connection is restored.
Once the connection is restored, the client sends any pending write operations it has in the order in which the client performed them.
It then handles the response from the server, which (if the server rejects the operation because of security rules) may lead to firing more local events so that the app can put the UI back into the correct sate.
And it then finally calls any completion listeners, and resolves or rejects the promise for the set(), push(), update(), or remove() method.
You'll note that there is no error raised at any point for a lack of an internet connection.
If you don't want to send any data to the local queue when the app has no internet connection, it's best to detect if the Firebase client is connected to the server. You can do this by listening to the .info/connected pseudo-node. This covers more than just having an internet connection btw, but also cases where the internet connections works but the client can't reach Firebase. The best practice here is to use a "global" listener for this status, and disable the relevant UI elements if the client is not connected.
I am developing angular(2) application.
And I want to update view when data changed in back end.
getData() {
return this.http.get("some url")
.map(result => result.json());
}
How can I develop listener in my component, which will be listen and updating view?
So, two solutions depending on what you are able to do:
1 - You have write access to the server's code
Then you can implement the websocket support on your server and then use a tool like https://github.com/ohjames/rxjs-websockets to automatically wrap the socket events in rxjs observables.
2 - You don't have write access to the server's code
Well, in this case, you will have to do a regular polling of the server. Which would look something like that:
Rx
.Observable
.timer(0, 1000) // once every second
.mergeMap(_ => this.http.get("/url").map(json => result.json()))
If the server is well implemented (and you send the right headers), it might send you back a 304 http code from which you can deduce that nothing happened since your last call, and you can filter out those cases.
Hope it helps
I have breezeJs running in an angular app on mobile device (cordova), which talks to .Net WebApi.
Everything works great, except once in a while the device will get PrimaryKey violations (from my SQL Server).
I think I narrowed it down to only happening when data connection is shakey on the device.
The only way I can figure these primary key violations are happening is somehow the server is Saving Changes, but the mobile connection drops out before the response can come back from server that everything saved OK.
What is supposed to happen when BreezeJS doesn't hear back from server after calling SaveChanges?
Anyone familiar with BreezeJS know of a way to handle this scenario?
I've had to handle the same scenario in my project. The approach I took was two part:
Add automatic retries to failed ajax requests. I'm using breeze with jQuery, so I googled "jQuery retry ajax". There's many different implementations, mine is somewhat custom, all center around hijacking the onerror callback as well as the deferred's fail handler to inject retry logic. I'm sure Angular will have similar means of retrying dropped requests.
In the saveChanges fail handler, add logic like this:
...
function isConcurrencyException(reason: any) {
return reason && reason.message && /Store update, insert, or delete statement affected an unexpected number of rows/.test(reason.message);
}
function isConnectionFailure(reason: any): boolean {
return reason && reason.hasOwnProperty('status') && reason.status === 0
}
entityManager.saveChanges()
.then(... yay ...)
.fail(function(reason) {
if (isConnectionFailure(reason)) {
// retry attempts failed to reach server.
// notify user and save to local storage....
return;
}
if (isConcurrencyException(reason)) {
// EF is not letting me save the entities again because my previous save (or another user's save) moved the concurrency stamps on the record. There's also the possibility that a record I'm try to save was deleted by another user.
// recover... in my case I kept it simple and simply attempt to reload the entity. If nothing is returned I know the entity was deleted. Otherwise I now have the latest version. In either case a message is shown to the user.
return;
}
if (reason.entityErrors) {
// We have an "entityErrors" property... this means the saved failed due to server-side validation errors.
// do whatever you do to handle validation errors...
return;
}
// an unexpected exception. let it bubble up.
throw reason;
})
.done(); // terminate the promise chain (may not be an equivalent in Angular, not sure).
One of the ways you can test spotty connections is to use Fiddler's AutoResponder tab. Set up a *.drop rule with a regex that matches your breeze route and check the "Enable Automatic Responses" box when you want to simulate dropped requests.
This is a somewhat messy problem to solve- no one size fits all answer, hope this helps.
NOTE
Ward makes a good point in the comments below. This approach is not suitable in situations where the entity's primary key is generated on the server (which would be the case if your db uses identity columns for PKs) because the retry logic could cause duplicate inserts.
I need users to be able to post data from a single page browser application (SPA) to me, but I can't put server-side code on the host.
Is there a web service that I can use for this? I looked at Amazon SQS (simple queue service) but I can't call their REST APIs from within the browser due to cross origin policy.
I favour ease of development over robustness right now, so even just receiving an email would be fine. I'm not sure that the site is even going to catch on. If it does, then I'll develop a server-side component and move hosts.
Not only there are Web Services, but nowadays there are robust systems that provide a way to server-side some logic on your applications. They are called BaaS or Backend as a Service providers, usually to provide some backbone to your front end applications.
Although they have multiple uses, I'm going to list the most common in my opinion:
For mobile applications - Instead of having to learn an API for each device you code to, you can use an standard platform to store logic and data for your application.
For prototyping - If you want to create a slick application, but you don't want to code all the backend logic for the data -less dealing with all the operations and system administration that represents-, through a BaaS provider you only need good Front End skills to code the simplest CRUD applications you can imagine. Some BaaS even allow you to bind some Reduce algorithms to calls your perform to their API.
For web applications - When PaaS (Platform as a Service) came to town to ease the job for Backend End developers in order to avoid the hassle of System Administration and Operations, it was just logic that the same was going to happen to the Backend. There are many clones that showcase the real power of this strategy.
All of this is amazing, but I have yet to mention any of them. I'm going to list the ones that I know the most and have actually used in projects. There are probably many, but as far as I know, this one have satisfied most of my news, whether it's any of the previously ones mentioned.
Parse.com
Parse's most outstanding features target mobile devices; however, nowadays Parse contains an incredible amount of API's that allows you to use it as full feature backend service for Javascript, Android and even Windows 8 applications (Windows 8 SDK was introduced a few months ago this year).
How does a Parse code looks in Javascript?
Parse works through classes and objects (ain't that beautiful?), so you first create a specific class (can be done through Javascript, REST or even the Data Browser manager) and then you add objects to specific classes.
First, add up Parse as a script tag in javascript:
<script type="text/javascript" src="http://www.parsecdn.com/js/parse-1.1.15.min.js"></script>
Then, through a given Application ID and a Javascript Key, initialize Parse.
Parse.initialize("APPLICATION_ID", "JAVASCRIPT_KEY");
From there, it's all object manipulation
var Person = Parse.Object.extend("Person"); //Person is a class *cof* uppercase *cof*
var personObject = new Person();
personObject.save({name: "John"}, {
success: function(object) {
console.log("The object with the data "+ JSON.stringify(object) + " was saved successfully.");
},
error: function(model, error) {
console.log("There was an error! The following model and error object were provided by the Server");
console.log(model);
console.log(error);
}
});
What about authentication and security?
Parse has a User based authentication system, which pretty much allows you to store a base of users that can manipulate the data. If map the data with User information, you can ensure that only a given user can manipulate specific data. Plus, in the settings of your Parse application, you can specify that no clients are allowed to create classes, to ensure innecesary calls are performed.
Did you REALLY used in a web application?
Yes, it was my tool of choice for a medium fidelity prototype.
Firebase.com
Firebase's main feature is the ability to provide Real Time to your application without all the hassle. You don't need a MeteorJS server in order to bring Push Notifications to your software. If you know Javascript, you are half way through to bring Real Time magic to your users.
How does a Firebase looks in Javascript?
Firebase works in a REST fashion, and I think they do an amazing job structuring the Glory of REST. As a good example, look at the following Resource structure in Firebase:
https://SampleChat.firebaseIO-demo.com/users/fred/name/first
You don't need to be a rocket scientist to know that you are retrieve the first name of the user "Fred", giving there's at least one -usually there should be a UUID instead of a name, but hey, it's an example, give me a break-.
In order to start using Firebase, as with Parse, add up their CDN Javascript
<script type='text/javascript' src='https://cdn.firebase.com/v0/firebase.js'></script>
Now, create a reference object that will allow you to consume the Firebase API
var myRootRef = new Firebase('https://myprojectname.firebaseIO-demo.com/');
From there, you can create a bunch of neat applications.
var USERS_LOCATION = 'https://SampleChat.firebaseIO-demo.com/users';
var userId = "Fred"; // Username
var usersRef = new Firebase(USERS_LOCATION);
usersRef.child(userId).once('value', function(snapshot) {
var exists = (snapshot.val() !== null);
if (exists) {
console.log("Username "+userId+" is part of our database");
} else {
console.log("We have no register of the username "+userId);
}
});
What about authentication and security?
You are in luck! Firebase released their Security API about two weeks ago! I have yet to explore it, but I'm sure it fills most of the gaps that allowed random people to use your reference to their own purpose.
Did you REALLY used in a web application?
Eeehm... ok, no. I used it in a Chrome Extension! It's still in process but it's going to be a Real Time chat inside a Chrome Extension. Ain't that cool? Fine. I find it cool. Anyway, you can browse more awesome examples for Firebase in their examples page.
What's the magic of these services? If you read your Dependency Injection and Mock Object Testing, at some point you can completely replace all of those services for your own through a REST Web Service provider.
Since these services were created to be used inside any application, they are CORS ready. As stated before, I have successfully used both of them from multiple domains without any issue (I'm even trying to use Firebase in a Chrome Extension, and I'm sure I will succeed soon).
Both Parse and Firebase have Data Browser managers, which means that you can see the data you are manipulating through a simple web browser. As a final disclaimer, I have no relationship with any of those services other than the face that James Taplin (Firebase Co-founder) was amazing enough to lend me some Beta access to Firebase.
You actually CAN use SQS from the browser, even without CORS, as long as you only need the browser to send messages, not receive them. Warning: this is a kludge that would make my CS professors cry.
When you perform a GET request via javascript, the browser will always perform the request, however, you'll only get access to the response if it was from the same origin (protocol, host, port). This is your ticket to ride, since messages can be posted to an SQS queue with just a GET, and who really cares about the response anyways?
Assuming you're using jquery, your queue is https://sqs.us-east-1.amazonaws.com/71717171/myqueue, and allows anyone to post a message, the following will post a message with the body "HITHERE" to the queue:
$.ajax({
url: 'https://sqs.us-east-1.amazonaws.com/71717171/myqueue' +
'?Action=SendMessage' +
'&Version=2012-11-05' +
'&MessageBody=HITHERE'
})
The'll be an error in the console saying that the request failed, but the message will show up in the queue anyways.
Have you considered JSONP? That is one way of calling cross-domain scripts from javascript without running into the same origin policy. You're going to have to set up some script somewhere to send you the data, though. Javascript just isn't up to the task.
Depending in what kind of data you want to send, and what you're going to do with it, one way of solving it would be to post the data to a Google Spreadsheet using Ajax. It's a bit tricky to accomplish though.Here is another stackoverflow question about it.
If presentation isn't that important you can just have an embedded Google Spreadsheet Form.
What about mailto:youremail#goeshere.com ? ihihi
Meantime, you can turn on some free hostings like Altervista or Heroku or somenthing else like them .. so you can connect to their server , if i remember these free services allows servers p2p, so you can create a sort of personal web services and push ajax requests as well, obviously their servers are slow for free accounts, but i think it's enought if you do not have so much users traffic, else you should turn on some better VPS or Hosting or Cloud solution.
Maybe CouchDB can provide what you're after. IrisCouch provides free CouchDB instances. Lock it down so that users can't view documents and have a sensible validation function and you've got yourself an easy RESTful place to stick your data in.