I'm trying to create simple notification system for my site admin, and I need to send only real-time messages to every admin user. But when I use firebase it loads old data on every page, and user see all messages from database. If I set limit(1) user will see last notification on every page reloading:
var eventsList = new Firebase('https://*****-messages.firebaseio.com/');
eventsList.on('child_added', function(message) {
var message = message.val();
$.notification(message.message);
});
How I can load only new messages, without old notification history?
This is by design, in a real-time system there is no concept of the "latest" data because it's always changing. However, if you want to only display items added to the list after the page has loaded, you can do the following:
var newItems = false;
var eventsList = new Firebase('https://*****-messages.firebaseio.com/');
eventsList.on('child_added', function(message) {
if (!newItems) return;
var message = message.val();
$.notification(message.message);
});
eventsList.once('value', function(messages) {
newItems = true;
});
I would comment on the above, but due to reputation I cannot, so hoping this is adequate and this is to address the last comment by Gruff McGruff.
Once fires after because you want to break out of the loop of grabbing all child items. Once that loops is broken, you'll set the newItems variable to true, and then it will be able to get all new children after that.
If you fired it before, it would defeat the purpose and grab all child items regardless because you'll set the newItems variable immediately.
Also, I've used this approach and it works well.
Related
I have a page that lets you edit user data. I'm using FlowRouter for the routing and it can be found on the route /employees/:id.
I need to update the detail form when data changes on the server and leave the route if it was deleted by other client.
I decided to use Tracker.autorun which informs me whenever the data changes. The previous user info is stored on the template so it's easy to tell if the record was deleted.
Template.UpdateEmployee.onCreated(function () {
const self = this;
self.subscribe('user', FlowRouter.getParam('id'));
self.autorun(function () {
const _id = FlowRouter.getParam('id');
const user = Meteor.users.findOne({_id});
if(!user && self.user)
FlowRouter.go('/employees');
self.user = user;
if(!user)
return;
user.email = user.emails[0].address;
$('.ui.form').form('set values',user);
});
});
And lastly in the onRendered callback I'm checking if the data was set on template as I believe not doing so could lead to data being available before the template is rendered and hence values wouldn't get set properly. Is this correct?
Template.UpdateEmployee.onRendered(function () {
if(this.user){
user.email = user.emails[0].address;
$('.ui.form').form('set values',user);
}
});
Are there any pitfalls to this solution?
I can see a couple drawbacks inherently. The first one is doing a find query on the client. Typically you would want to return data from the server using Meteor publish and subscribe.
The second is you are passing the key to find the data over the URL. This can be spoofed by other users for them to find that users data.
Lastly if you are doing a find on the user object, I assume you might be storing data there. This is generally bad practice. If you need to store user data with their profile, it's best to create a new collection and publish/subscribe what you need.
I want to use
// client
var limit = Session.get('postsLimit');
Tracker.autorun(function (c) {
Meteor.subcribe('posts', limit);
c.stop();
});
// server
Meteor.publish('posts', function (limit) {
return Posts.find({}, {limit: limit});
});
because I don't want the insertion of new posts to affect a user's experience while viewing the posts that were loaded when a user first visits the page. But at the same time, I want the tracker to still recognize limit changes so that it can load posts as the user scrolls. So in other words, I want the tracker to stop subscribing to brand new post after the initial load but still load posts that have already been created.
How can I do this with Tracker or perhaps Tracker isn't the best option?
You could create a client only collection, insert the posts into that and make your helpers return the local collection.
Use observeChanges to watch the for newly added posts, when there are new posts, show the user an appropriate message. When the user wants to view the new posts, add them to the client only collection.
How about this:
//client.js
var now = new Date(); //so the now never change
Tracker.autorun(function (c) {
Meteor.subscribe('posts', now, Session.get('postsLimit'));
});
//server.js
Meteor.publish('posts',function(time,limit){
return Posts.find({savedAt: {$lt: time}},{limit:limit});
});
So when each post is saved into the database, a savedAt field is also appended and the query only searches for those saved before the current time.
Instead of using var now = new Date(); you can also use Session.get('now') then you can change it later by Session.set('now',new Date) when a user decides to fetch everything new.
However have to be aware of the time differences between client and server, may need to synchronise them?
I'm in the process of learning meteor. I followed the tutorial to create microscope. If some one submits a post meteor will re render the template for all users. This could be very annoying if there are hundreds of posts then the user will come back to the top of the page and loose track of where he was. I want to implement something similar to what facebook has. When a new post is submitted template isn't rendered rather, a button or link will appear. Clicking it will cause the template to re-render and show the new posts.
I was thinking of using observeChanges on the collection to detect any changes and it does stop the page from showing new posts but only way to show them is to reload the page.
Meteor.publish('posts', function(options) {
var self = this, postHandle = null;
var initializing = true;
postHandle = Posts.find({}, options).observeChanges({
added: function(id, post) {
if (initializing){
self.added('posts', id, post);
}
},
changed: function(id, fields) {
self.changed('posts', id, fields);
}
});
self.ready();
initializing = false;
self.onStop(function() { postHandle.stop(); });
});
Is this the right path to take? If yes, how do I alert the user of new posts? Else, what would be a better way to implement this?
Thank you
This is a tricky question but also valuable as it pertains to a design pattern that is applicable in many instances. One of the key aspects is wanting to know that there is new data but not wanting to show it (yet) to the user. We can also assume that when the user does want to see the data, they probably don't want to wait for it to be loaded into the client (just like Facebook). This means that the client still needs to cache the data as it arrives, just not display it immediately.
Therefore, you probably don't want to restrict the data displayed in the publication - because this won't send the data to the client. Rather, you want to send all the (relevant) data to the client and cache it there until it is ready.
The easiest way involves having a timestamp in your data to work from. You can then couple this with a Reactive Variable to only add new documents to your displayed set when that Reactive Variable changes. Something like this (code will probably be in different files):
// Within the template where you want to show your data
Template.myTemplate.onCreated(function() {
var self = this;
var options = null; // Define non-time options
// Subscribe to the data so everything is loaded into the client
// Include relevant options to limit data but exclude timestamps
self.subscribe("posts", options);
// Create and initialise a reactive variable with the current date
self.loadedTime = new ReactiveVar(new Date());
// Create a reactive variable to see when new data is available
// Create an autorun for whenever the subscription changes ready() state
// Ignore the first run as ready() should be false
// Subsequent false values indicate new data is arriving
self.newData = new ReactiveVar(false);
self.autorun(function(computation) {
if(!computation.firstRun) {
if(!self.subscriptionsReady()) {
self.newData.set(true);
}
}
});
});
// Fetch the relevant data from that subscribed (cached) within the client
// Assume this will be within the template helper
// Use the value (get()) of the Reactive Variable
Template.myTemplate.helpers({
displayedPosts = function() {
return Posts.find({timestamp: {$lt: Template.instance().loadedTime.get()}});
},
// Second helper to determine whether or not new data is available
// Can be used in the template to notify the user
newData = function() {
return Template.instance().newData.get();
});
// Update the Reactive Variable to the current time
// Assume this takes place within the template helper
// Assume you have button (or similar) with a "reload" class
Template.myTemplate.events({
'click .reLoad' = function(event, template) {
template.loadedTime.set(new Date());
}
});
I think this is the simplest pattern to cover all of the points you raise. It gets more complicated if you don't have a timestamp, you have multiple subscriptions (then need to use the subscription handles) etc. Hope this helps!
As Duncan said in his answer, ReactiveVar is the way to go. I've actually implemented a simple facebook feed page with meteor where I display the public posts from a certain page. I use infinite scroll to keep adding posts to the bottom of the page and store them in a ReactiveVar. Check the sources on github here and the live demo here. Hope it helps!
The application shows work-shifts for certain time-period. firebaseConn.getShifts is the API-function to get the shiftData for the given time period.
versions:
firebase: 2.0.6
angularFire: 0.9.0 (confirmed with 0.8.2 also)
This is my firebase schema:
And this is the code:
.factory('watchers', function(bunch-of-dependencies) {
var unbindShifts = function() {};
var inited = false;
var shifts = {};
... some irrelevant code in between ...
function initShifts() {
unbindShifts();
shifts.object = firebaseConn.getShifts( false, from, to, $scope );
$scope.shifts = shifts.object;
shifts.object.$bindTo($scope, "shifts").then(function(unbind) {
unbindShifts = unbind;
});
}
The firebase-queries (that have worked fine before adding the unbind / bind and possibly time-based querying might cause issues too):
firebaseConn.getShifts = function(asArray, from, to, scope) {
return cacheRequest(FBURL + "shifts", asArray, [from, to]);
};
function cacheRequest(url, asArray, limits) {
var type = asArray ? "array" : "object";
var startAt = limits ? limits[0] : undefined;
var endAt = limits ? limits[1] : undefined;
var retObj, FBRef;
cached[url] = cached[url] || {};
/* If there are limits-parameters we don't cache at all atm. Since those queries should be checked differently than static urls */
if(!limits && cached[url][type]) {
FBRef = cached[url][type];
} else {
FBRef = cached[url][type] = createFBRef(url, startAt, endAt);
}
if(asArray) {
retObj = FBRef.$asArray();
} else {
retObj = FBRef.$asObject();
}
return retObj;
}
function createFBRef(resourceURL, startAt, endAt) {
var modifiedObject = $firebase( createRef( resourceURL ).orderByKey().startAt(startAt).endAt(endAt) );
return modifiedObject;
}
function createRef(resourceURL) {
return new Firebase( resourceURL );
}
Now I have located the problem to be with the query limiting. If the from and to Dates are undefined, this works without problems. But I need to be able to limit the amount of data, since loading many years of workshift-data, to show a weeks time, won't be good :).
The actual problem is not displaying and fetching the data, everything works fine, it's related to the times and re-binding.
If I do any changes to e.g. "20150115"-table. For example I add another "groups"-child there. When i unbind and rebind, the whole "20150115"-table gets deleted and this holds true only to the latest changes. If I add multiple child to different dates e.g. "20150113", "20150114", "20150115" and the latest change is in "20150115" and then I unbind + re-bind another time from firebase, all the other root-paths will stay as they are, but the latest change in "20150115" will make the whole tree deleted.
I hope I make myself clear, so for safety I try to explain it again in simpler way.
- Changes to 1. "20150113", 2. "20150114", 3. "20150115" through the app.
- Changing timeline from UI causes: unbind + re-bind
- As a side-effect the whole "20150114" tree gets deleted.
The problem is somehow related to advanced querying with orderByKey().startAt(startAt).endAt(endAt) and binding.
Also for additional info. The data which is added through the UI gets added to the firebase database, but when the re-binding happens, the data is deleted from the database. Specifically on rebind, unbinding causes no issues, if I delay rebinding with timeout.
EDIT:
I have found the source of the actual issue. After the new binding is in place and everything seems to be in order, there is an angular watch event that kicks in. The event tries to save the last change user made before re-binding.
So if I have and active timeline for december (20141201 - 20141230) and I change "20141225"-data. Then change the timeline to 20150101 - 20150130, causing unbind and rebind (or manually fetching new data). There will be an event, after the binding has been done and everything seems to be in order, trying to save 20141225 data to either the new timeline (20150101 - 20150130) or the old one, not sure which one. This causes the firebase to actually delete the whole 20141225-tree, instead of saving the data.
The new data makes it into your Firebase fine, which you can see by either checking your Firebase dashboard or by running a quick snippet like this in your browser's dev console:
new Firebase("https://firebaseurl").once('value', function(s) { console.log(s.val()); })
The data even makes it back into your application. The only problem is that Angular doesn't know that new data has arrived, so it doesn't update the view with the new data.
Normally AngularFire's $asObject and $asArray methods take care of notifying AngularJS when new data arrives from Firebase. But since you are constantly creating new queries, you'll have to take care of that yourself.
There are a few ways to signal the new data to AngularJS and I'm definitely not an expert on which one is best. But if you add $scope.$apply(); to your setDays function it works:
function setDays(ref) {
var FBRange = setFBRange(ref, from, to);
var days;
unbindDays();
days = $firebase(FBRange).$asObject();
$scope.days = days;
days.$bindTo($scope, "days").then(function(unbind) {
unbindDays = unbind;
// As a result of the new binding entry gets mysteriously deleted from firebase
});
$scope.$apply(); // Tell AngularJS about the new data, so that it updates the view
function setFBRange(ref, from, to) {
return ref.orderByKey().startAt(""+from).endAt(from + to + "");
}
}
Updated Plunkr with this change (and some others to help in debugging): http://plnkr.co/edit/YZtkzUNtjQUCcw4xb2mj?p=preview
I'm making a simple app that informs a client that other clients clicked a button. I'm storing the clicks in a Firebase (db) using:
db.push({msg:data});
All clients get notified of other user's clicks with an on, such as
db.on('child_added',function(snapshot) {
var msg = snapshot.val().msg;
});
However, when the page first loads I want to discard any existing data on the stack. My strategy is to call db.once() before I define the db.on('child_added',...) in order to get the initial number of children, and then use that to discard that number of calls to db.on('child_added',...).
Unfortunately, though, all of the calls to db.on('child_added',...) are happening before I'm able to get the initial count, so it fails.
How can I effectively and simply discard the initial data?
For larger data sets, Firebase now offers (as of 2.0) some query methods that can make this simpler.
If we add a timestamp field on each record, we can construct a query that only looks at new values. Consider this contrived data:
{
"messages": {
"$messageid": {
"sender": "kato",
"message": "hello world"
"created": 123456 // Firebase.ServerValue.TIMESTAMP
}
}
}
We could find messages only after "now" using something like this:
var ref = new Firebase('https://<your instance>.firebaseio.com/messages');
var queryRef = ref.orderBy('created').startAt(Firebase.ServerValue.TIMESTAMP);
queryRef.on('child_added', function(snap) {
console.log(snap.val());
});
If I understand your question correctly, it sounds like you only want data that has been added since the user visited the page. In Firebase, the behavior you describe is by design, as the data is always changing and there isn't a notion of "old" data vs "new" data.
However, if you only want to display data added after the page has loaded, try ignoring all events prior until the complete set of children has loaded at least once. For example:
var ignoreItems = true;
var ref = new Firebase('https://<your-Firebase>.firebaseio.com');
ref.on('child_added', function(snapshot) {
if (!ignoreItems) {
var msg = snapshot.val().msg;
// do something here
}
});
ref.once('value', function(snapshot) {
ignoreItems = false;
});
The alternative to this approach would be to write your new items with a priority as well, where the priority is Firebase.ServerValue.TIMESTAMP (the current server time), and then use a .startAt(...) query using the current timestamp. However, this is more complex than the approach described above.