I'm wondering if given example could meet racing condition on a real server, does work on localhost. Given situation- user deletes a few person from a form ( lets say studyForm and studyPersons ) Ive added personToDelete to an array an later on- Edit Action im deleting them in a loop
// A punch of persons chosen to be deleted
self.markedForDeleted.forEach(function(trashed){
trashed.destroyRecord();
});
this.get('person').save().then(personEditSuccess, personEditFailure);
Should i edit it like this ?
var onDeleteSuccess = function(wasAnyToDelete){
if (wasAnyToDelete){
deletedPersons ++;
}
if(deletedPersons === lengthOfAllPersons) {
this.get('person').save().then(personEditSuccess, personEditFailure);
}
};
// A punch of persons chosen to be deleted
self.markedForDeleted.forEach(function(trashed){
trashed.destroyRecord().then(onDeleteSuccess, onDeleteFailure);
});
Working and currently using
Ember.RSVP.all(personsToDelete.invoke('destroyRecord')).then(deletePersonSuccess, deletePersonFailure);
Related
You can get the child count via
firebase_node.once('value', function(snapshot) { alert('Count: ' + snapshot.numChildren()); });
But I believe this fetches the entire sub-tree of that node from the server. For huge lists, that seems RAM and latency intensive. Is there a way of getting the count (and/or a list of child names) without fetching the whole thing?
The code snippet you gave does indeed load the entire set of data and then counts it client-side, which can be very slow for large amounts of data.
Firebase doesn't currently have a way to count children without loading data, but we do plan to add it.
For now, one solution would be to maintain a counter of the number of children and update it every time you add a new child. You could use a transaction to count items, like in this code tracking upvodes:
var upvotesRef = new Firebase('https://docs-examples.firebaseio.com/android/saving-data/fireblog/posts/-JRHTHaIs-jNPLXOQivY/upvotes');
upvotesRef.transaction(function (current_value) {
return (current_value || 0) + 1;
});
For more info, see https://www.firebase.com/docs/transactions.html
UPDATE:
Firebase recently released Cloud Functions. With Cloud Functions, you don't need to create your own Server. You can simply write JavaScript functions and upload it to Firebase. Firebase will be responsible for triggering functions whenever an event occurs.
If you want to count upvotes for example, you should create a structure similar to this one:
{
"posts" : {
"-JRHTHaIs-jNPLXOQivY" : {
"upvotes_count":5,
"upvotes" : {
"userX" : true,
"userY" : true,
"userZ" : true,
...
}
}
}
}
And then write a javascript function to increase the upvotes_count when there is a new write to the upvotes node.
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);
exports.countlikes = functions.database.ref('/posts/$postid/upvotes').onWrite(event => {
return event.data.ref.parent.child('upvotes_count').set(event.data.numChildren());
});
You can read the Documentation to know how to Get Started with Cloud Functions.
Also, another example of counting posts is here:
https://github.com/firebase/functions-samples/blob/master/child-count/functions/index.js
Update January 2018
The firebase docs have changed so instead of event we now have change and context.
The given example throws an error complaining that event.data is undefined. This pattern seems to work better:
exports.countPrescriptions = functions.database.ref(`/prescriptions`).onWrite((change, context) => {
const data = change.after.val();
const count = Object.keys(data).length;
return change.after.ref.child('_count').set(count);
});
```
This is a little late in the game as several others have already answered nicely, but I'll share how I might implement it.
This hinges on the fact that the Firebase REST API offers a shallow=true parameter.
Assume you have a post object and each one can have a number of comments:
{
"posts": {
"$postKey": {
"comments": {
...
}
}
}
}
You obviously don't want to fetch all of the comments, just the number of comments.
Assuming you have the key for a post, you can send a GET request to
https://yourapp.firebaseio.com/posts/[the post key]/comments?shallow=true.
This will return an object of key-value pairs, where each key is the key of a comment and its value is true:
{
"comment1key": true,
"comment2key": true,
...,
"comment9999key": true
}
The size of this response is much smaller than requesting the equivalent data, and now you can calculate the number of keys in the response to find your value (e.g. commentCount = Object.keys(result).length).
This may not completely solve your problem, as you are still calculating the number of keys returned, and you can't necessarily subscribe to the value as it changes, but it does greatly reduce the size of the returned data without requiring any changes to your schema.
Save the count as you go - and use validation to enforce it. I hacked this together - for keeping a count of unique votes and counts which keeps coming up!. But this time I have tested my suggestion! (notwithstanding cut/paste errors!).
The 'trick' here is to use the node priority to as the vote count...
The data is:
vote/$issueBeingVotedOn/user/$uniqueIdOfVoter = thisVotesCount, priority=thisVotesCount
vote/$issueBeingVotedOn/count = 'user/'+$idOfLastVoter, priority=CountofLastVote
,"vote": {
".read" : true
,".write" : true
,"$issue" : {
"user" : {
"$user" : {
".validate" : "!data.exists() &&
newData.val()==data.parent().parent().child('count').getPriority()+1 &&
newData.val()==newData.GetPriority()"
user can only vote once && count must be one higher than current count && data value must be same as priority.
}
}
,"count" : {
".validate" : "data.parent().child(newData.val()).val()==newData.getPriority() &&
newData.getPriority()==data.getPriority()+1 "
}
count (last voter really) - vote must exist and its count equal newcount, && newcount (priority) can only go up by one.
}
}
Test script to add 10 votes by different users (for this example, id's faked, should user auth.uid in production). Count down by (i--) 10 to see validation fail.
<script src='https://cdn.firebase.com/v0/firebase.js'></script>
<script>
window.fb = new Firebase('https:...vote/iss1/');
window.fb.child('count').once('value', function (dss) {
votes = dss.getPriority();
for (var i=1;i<10;i++) vote(dss,i+votes);
} );
function vote(dss,count)
{
var user='user/zz' + count; // replace with auth.id or whatever
window.fb.child(user).setWithPriority(count,count);
window.fb.child('count').setWithPriority(user,count);
}
</script>
The 'risk' here is that a vote is cast, but the count not updated (haking or script failure). This is why the votes have a unique 'priority' - the script should really start by ensuring that there is no vote with priority higher than the current count, if there is it should complete that transaction before doing its own - get your clients to clean up for you :)
The count needs to be initialised with a priority before you start - forge doesn't let you do this, so a stub script is needed (before the validation is active!).
write a cloud function to and update the node count.
// below function to get the given node count.
const functions = require('firebase-functions');
const admin = require('firebase-admin');
admin.initializeApp(functions.config().firebase);
exports.userscount = functions.database.ref('/users/')
.onWrite(event => {
console.log('users number : ', event.data.numChildren());
return event.data.ref.parent.child('count/users').set(event.data.numChildren());
});
Refer :https://firebase.google.com/docs/functions/database-events
root--|
|-users ( this node contains all users list)
|
|-count
|-userscount :
(this node added dynamically by cloud function with the user count)
I want to load all the items on start without showing any message, but once after loaded. I want to capture any new row in subscriber and show it to the desktop notification.
The problem is, I'm not sure how to check if all the previous items are loaded and if the row is new item or is it from previous existing item.
this.items = this.af.database.list('notifications/'+this.uid+'/');
this.items.subscribe(list => {
list.forEach(row => {
// doing something here...
});
// once all the rows are finished loading, then any new row, show desktop notification message
});
I have user lodash for the minimal code.
// this varible holds the initial loaded keys
let loadedKeys = [];
this.items = this.af.database.list('notifications/'+this.uid+'/');
this.items.subscribe((list)=>{
// we skip it while initial load
if(!_.isEmpty(loadedKeys)){
// different is the new keys
let newKeys = _.difference(_.map(list, "$key"), loadedKeys);
if(!_.isEmpty(newKeys)){
// ... notification code here
}
}
loadedKeys = _.map(list, "$key");
});
The behave you are looking for is the default Subject approach in RxJS.
Check this reactiveX url to follow the marble diagram of Publish Subject (the equivalent for Subject in RxJS).
So you have two easy options:
1) manually index witch rows you want to display like #bash replied
2) create a Rx.Subject() and assign only the newest's rows to it. Then you subscribe to this subject in your app workflow.
The advantage of method 2 is when a new .subscribe occur, it will not retrieve previous data.
Edit: I wrote this codepen as a guide to implement your custom RxJS Subject. Hope it helps.
Assuming your rows have something unique to match with previous rows you can do the following:
// A Row item has a unique identifier id
interface Row {
id: number;
}
this.rows: Row[];
this.items$ = this.af.database.list(`notifications/${this.uid}/`).pipe(
tap(list => {
// if rows is not array, first time...
if(!Array.isArray(this.rows)) {
// first time nothing to do
return;
}
// returns true if some item from list is not found in this.rows
const foundNewRow = list.some(item => {
return ! this.rows.find(row => row.id === item.id);
});
if (foundNewRow) {
// call method to show desktop message here
}
}
);
I used a pipe and a tap operator (that you will have to import). If you subscribe to this.items$ the tap operator will do the work:
this.items$.subscribe((items => this.rows = items));
If you do not want to set this.rows when normally subscribing than you can also do this in the tap operator. But that would assume you only use it for checking difference between existing and new items.
Let's say that two users do changes to the same document while offline, but in different sections of the document. If user 2 goes back online after user 1, will the changes made by user 1 be lost?
In my database, each row contains a JS object, and one property of this object is an array. This array is bound to a series of check-boxes on the interface. What I would like is that if two users do changes to those check-boxes, the latest change is kept for each check-box individually, based on the time the when the change was made, not the time when the syncing occurred. Is GroundDB the appropriate tool to achieve this? Is there any mean to add an event handler in which I can add some logic that would be triggered when syncing occurs, and that would take care of the merging ?
The short answer is "yes" none of the ground db versions have conflict resolution since the logic is custom depending on the behaviour of conflict resolution eg. if you want to automate or involve the user.
The old Ground DB simply relied on Meteor's conflict resolution (latest data to the server wins) I'm guessing you can see some issues with that depending on the order of when which client comes online.
Ground db II doesn't have method resume it's more or less just a way to cache data offline. It's observing on an observable source.
I guess you could create a middleware observer for GDB II - one that checks the local data before doing the update and update the client or/and call the server to update the server data. This way you would have a way to handle conflicts.
I think to remember writing some code that supported "deletedAt"/"updatedAt" for some types of conflict handling, but again a conflict handler should be custom for the most part. (opening the door for reusable conflict handlers might be useful)
Especially knowing when data is removed can be tricky if you don't "soft" delete via something like using a "deletedAt" entity.
The "rc" branch is currently grounddb-caching-2016 version "2.0.0-rc.4",
I was thinking about something like:
(mind it's not tested, written directly in SO)
// Create the grounded collection
foo = new Ground.Collection('test');
// Make it observe a source (it's aware of createdAt/updatedAt and
// removedAt entities)
foo.observeSource(bar.find());
bar.find() returns a cursor with a function observe our middleware should do the same. Let's create a createMiddleWare helper for it:
function createMiddleWare(source, middleware) {
const cursor = (typeof (source||{}).observe === 'function') ? source : source.find();
return {
observe: function(observerHandle) {
const sourceObserverHandle = cursor.observe({
added: doc => {
middleware.added.call(observerHandle, doc);
},
updated: (doc, oldDoc) => {
middleware.updated.call(observerHandle, doc, oldDoc);
},
removed: doc => {
middleware.removed.call(observerHandle, doc);
},
});
// Return stop handle
return sourceObserverHandle;
}
};
}
Usage:
foo = new Ground.Collection('test');
foo.observeSource(createMiddleware(bar.find(), {
added: function(doc) {
// just pass it through
this.added(doc);
},
updated: function(doc, oldDoc) {
const fooDoc = foo.findOne(doc._id);
// Example of a simple conflict handler:
if (fooDoc && doc.updatedAt < fooDoc.updatedAt) {
// Seems like the foo doc is newer? lets update the server...
// (we'll just use the regular bar, since thats the meteor
// collection and foo is the grounded data
bar.update(doc._id, fooDoc);
} else {
// pass through
this.updated(doc, oldDoc);
}
},
removed: function(doc) {
// again just pass through for now
this.removed(doc);
}
}));
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!
I'm trying to write a webapp using Meteor and I'm definitely failing to grok something about subscribing to published datasets. The entire app is up on github (linked to the latest commit for posterity), but I'll try to summarize below.
I have a collection called teams which is available to both client and server:
Teams = new Meteor.Collection( "teams" );
On the server, I want to publish a list of all of the teams:
Meteor.publish( "allteams", function() { ...
There's a very simple cursor which makes up this published list:
var handle = Teams.find( {} ).observeChanges({
added: function( id ) {
console.log( "New team added" );
if ( !initializing ) {
console.log( "Telling subscribers it's all change" );
self.added( "teams", id, {} );
self.ready();
}
}
});
The client subscribes to that source, and when elements are added the client will add pins to a map:
Meteor.autorun( function() {
Meteor.subscribe( "allteams", function() {
console.log( "All teams has been updated" );
// Do more stuff
}
};
When the list is initially populated the autorun runs fine, but if I add another element to the collection then the publisher method logs to say "I noticed this" but nothing happens in the subscriber.
The aim of the above is as follows:
There is a list of teams on the server which consists of a name and long/lat details
When a client connects, they receive that list of teams and they're plotted on a map
If a team is added to the list on the server side, each client is notified and a new pin appears on the map.
In terms of the app, I probably don't need pins to magically appear, but it's a useful way of learning publish and subscribe, especially when I don't get it right! Eventually, "allteams" will probably be a bit more fine-grained than just the entire list of teams, so I guess it's akin to making a view on the data.
Am I missing something completely obvious?
Edit: I worked it out and put the answer below. tl;dr I wasn't subscribing to a reactive data source at all.
It's probably not polite to answer my own question, but I worked out what I was doing wrong and I figured that other people might come across the same thing.
Simple answer is that I wasn't doing what I claimed to be doing in the title of the queston, specifically, not subscribing to a reactive data source.
Meteor.autorun( function() {
Meteor.subscribe( "allteams", function() {
console.log( "All teams has been updated" );
// Do more stuff
}
};
Here I've passed the subscribe method to autorun, but that method itself isn't a reactive data source. However, it returns something which is!
// Define a subscription
var handle = Meteor.subscribe( "foo", { onReady: function() { ... } } );
Meteor.autorun( function() {
if ( handle.ready() ) {
// Now do something every time the subscription is marked as ready
}
};
The ready method of a subscription handle is reactive, so the autorun now executes every time the published document set is updated. That leads me to further questions about the efficiency of multiple clients subscribing to a database cursor and watching for changes, but I'll come to that in another question.
If autopublish is still on, this may be the cause of your problems. Try disabling autopublish and seeing if the publish statement now works properly.