A few months back Firebase implemented promises in the database.
In that blog post there is an example of using a single transaction with promises:
var article;
var articleRef = ref.child('blogposts').child(id);
articleRef.once('value').then(function(snapshot) {
article = snapshot.val();
return articleRef.child('readCount').transaction(function(current) {
return (current || 0) + 1;
});
}).then(function(readCountTxn) {
renderBlog({
article: article,
readCount: readCountTxn.snapshot.val()
});
}, function(error) {
console.error(error);
});
Is it possible to chain multiple promises into a single transaction to be able to erase data only if everything can be erased?
Do you actually need a transaction or just an atomic operation? You can execute atomic operations on multiple paths simultaneously that will fail if something goes wrong with one of them (ie erase which is a write operation):
var ref = new Firebase("https://<YOUR-FIREBASE-APP>.firebaseio.com");
var updatedUserData = {};
updatedUserData["user/posts/location1"] = null;
updatedUserData["user/blogs/location2"] = null;
// Do a deep-path update
ref.update(updatedUserData).then(function() {
//yay
}, function(error) {
console.log("Error updating data:", error);
});
Transactions on the other hand are typically used for atomic data modifications where concurrent updates could cause an inconsistent data state. Imagine an upvote counter:
// user 1
upvotesRef.transaction(function (current_value) {
return (current_value || 0) + 1;
});
// user 2
upvotesRef.transaction(function (current_value) {
return (current_value || 0) + 1;
});
// upvotesRef will eventually be consistent with value += 2
Without transactions, you are not guaranteed this consistency:
// user 1
ref.on("value", function(snapshot) {
console.log(snapshot.val()); // oops, could be the same value as user 2!
ref.set(snapshot.val() + 1);
});
// user 2
ref.on("value", function(snapshot) {
console.log(snapshot.val()); // oops, could be the same value as user 1!
ref.set(snapshot.val() + 1);
});
More info here
Related
I am trying to retrieve the document for specific ids in the following cloud function. The loop (see "Block Get Major") for retrieving that information is running, but the logs show that it is executing AFTER the function returns data.
I am certain this is because this creates a new promise, and that I need to tie them together.
I've looked through a lot of the posts on here and elsewhere and am just not getting it.
It looks like I am creating a broken/dropped promise. I get the necessary data, with the exception of menteeMajor, which is undefined until later in the log files).
exports.getAllMatchesMCR = functions.https.onCall((data, context) => {
var dbRef = db.collection("matches");
var dbPromise = dbRef.get();
// return the main promise
return dbPromise.then(function(querySnapshot) {
var results = [];
var idx = 0;
querySnapshot.forEach(function(doc) {
// push promise from get into results
var matchObj = {
mentorName: "",
mentorEmployer: "",
mentees: []
}
var mentor = doc.data();
mentor.mentorID = doc.id;
matchObj.mentorName = mentor.mentorID;
matchObj.mentees = mentor.mentees;
for (var curIDX in matchObj.mentees) {
matchInfoObj = {};
matchInfoObj.mentorID = matchObj.mentorID;
matchInfoObj.mentorName = matchObj.mentorName;
matchInfoObj.menteeName = matchObj.mentees[curIDX];
// Block Get Major --->
var menteeRef = db.collection('users').doc(matchObj.mentees[curIDX]);
var getDoc = menteeRef.get()
.then(doc => {
if (!doc.exists) {
console.log('No such document!');
} else {
var userInfo = {};
userInfo = doc.data();
matchInfoObj.menteeMajor = userInfo.major;
// console.log('user Major:', matchInfoObj.menteeMajor);
return userInfo.major;
}
})
.catch(err => {
// console.log('Error getting document', err);
return ("No Mentee Doc")
});
console.log("in menteeInfo: ", getDoc.data());
matchInfoObj.menteeMajor = getDoc.data(); // Block Get Major <---
if (typeof something === "undefined") {
console.log('After BLOCK Major is UNDEFINED:', matchInfoObj.menteeName);
} else {
console.log('After BLOCK :', matchInfoObj.menteeMajor);
}
results.push(matchInfoObj)
}
});
// dbPromise.then() resolves to a single promise that resolves
// once all results have resolved
return Promise.all(results)
})
.catch(function(error) {
console.log("Error getting documents: ", error);
});
});
Here are two screen shots for the logs that show the order based on console.log output. Keep in mind that the sort of these log records is NEWEST at the top. Result 1 shows the start, from deployment of function and it's start, Result 2 shows the messages from the broken promise almost two minutes later.
The plain text version of what I'm trying to do is:
1. collection "Users" contains information on Mentees and Mentors
2. collection "Matches" is a doc of Mentees (array) for each Mentor, or One to Many).
3. Display one row for EACH mentor/mentee connection. I have the ids, but I need to get the names and other information for both mentees and mentors.
Plain old Result file shows that I am getting the rows I need with the Mentor ID, and the Mentee ID (labeled Mentees, that will change)
Can someone please show me the way to chain this promise?
I'm trying to run some code once all the jqXHR elements of an array are completed (have either succeeded or failed).
You can see the full code here: http://jsfiddle.net/Lkjcrdtz/4/
Basically I'm expecting the always hook from here:
$.when
.apply(undefined, reqs)
.always(function(data) {
console.log('ALL ALWAYS', data);
});
to run when all the requests that were piled up there have either succeeded or failed. Currently, you can observe in the console that ALL ALWAYS is logged earlier.
A simple solution for modern browsers would be to use the newer fetch() API along with Promise.all()
var makeReq = function(url, pos) {
var finalUrl = url + pos;
// intentionally make this request a failed one
if (pos % 2 === 0) {
finalUrl = "https://jsonplaceholder.typicode.com/423423rfvzdsv";
}
return fetch(finalUrl).then(function(resp) {
console.log('Request for user #', pos);
// if successful request return data promise otherwise return something
// that can be used to filter out in final results
return resp.ok ? resp.json() : {error: true, status: resp.status, id: pos }
})
};
// mock API
var theUrl = "https://jsonplaceholder.typicode.com/users/";
var reqs = [];
for (var i = 1; i <= 5; i++) {
reqs.push(makeReq(theUrl, i));
}
Promise.all(reqs).then(function(results) {
console.log('---- ALL DONE ----')
// filter out good requests
results.forEach(function(o) {
if (o.error) {
console.log(`No results for user #${o.id}`);
} else {
console.log(`User #${o.id} name = ${o.name}`);
}
})
})
I am rewriting a website of mine, to JavaScript in combination with Firebase. So far, I love Firebase, but now I am on a part where I need to migrate all of my old users to the Firebase system.
All the users have custom extra settings and i wan't to take down the server where it's on now (€ 103, p/m). So I need it all to be copied. As far as I know, it needs to be done one by one (createUserWithEmailAndPassword). On the server, I make a JSON object and on the new site I do:
$.get("/alljsonfromalink", function (rdata) {
var $jData = jQuery.parseJSON(rdata);
var i = 0;
for (var user in $jData) {
whenYouFeelLikIt(user, $jData);
}
});
function whenYouFeelLikIt(i, $jData) {
setTimeout(function() {
firebase.auth().signInWithEmailAndPassword($jData[i].email, RandomPassword)
.then(function(){
console.log("Succes Login");
//if exist i set extra settings
setusersettings($jData[i], $jData[i].email);
})
.catch(function(error) {
var errorCode = error.code;
console.log(errorCode);
if(errorCode == "auth/user-not-found") {
firebase.auth().createUserWithEmailAndPassword($jData[i].email, RandomPassword).then(function () {
console.log("Created: " + $jData[i].email);
});
}
});
},2000 * (i));
}
It works, but even with a 2-second timeout, I got after 20 or 30 inserts:
firebase.js:73 Uncaught Error: We have blocked all requests from this device due to unusual activity. Try again later.
Anyone has an idea how to work around this?
--Update--
JamieB suggested to use .fetchProvidersForEmail() So now I use
firebase.auth().fetchProvidersForEmail($jData[i].email)
.then(function(succes){
console.log(succes.length);
if(succes.length == 0) {
// the createUserWithEmailAndPassword() with timeout
create(i, $jData);
}
})
FIREBASE REFERENCE indicates that createUserWithEmailAndPassword(email, password) returns firebase.Promise containing non-null firebase.User. So, it returns a promise. These can be pushed into an array that can be handed to the .all Promise method. You can use the below function to add the username and photoURL to the Auth subsystem where they will be stored.
Any additional user properties can be store under a users node where each child id is the UID of the user. The script at the bottom shows an example of using Promise.all.
function registerPasswordUser(email,displayName,password,photoURL){
var user = null;
//NULLIFY EMPTY ARGUMENTS
for (var i = 0; i < arguments.length; i++) {
arguments[i] = arguments[i] ? arguments[i] : null;
}
auth.createUserWithEmailAndPassword(email, password)
.then(function () {
user = auth.currentUser;
user.sendEmailVerification();
})
.then(function () {
user.updateProfile({
displayName: displayName,
photoURL: photoURL
});
})
.catch(function(error) {
console.log(error.message);
});
console.log('Validation link was sent to ' + email + '.');
}
...an example of Promise.all:...
function loadMeetings(city,state) {
return ref.child('states').child(state).child(city).once('value').then(function(snapshot) {
var reads = [];
snapshot.forEach(function(childSnapshot) {
var id = childSnapshot.key();
var promise = ref.child('meetings').child(id).once('value').then(function(snap) {
return snap.val();
}, function(error) {
// The Promise was rejected.
console.error(error);
});
reads.push(promise);
});
return Promise.all(reads);
}, function(error) {
// The Promise was rejected.
console.error(error);
}).then(function(values) {
//for each snapshot do something
});
}
I'm new to promises and I'm sure there's an answer/pattern out there but I just couldn't find one that was obvious enough to me to be the right one. I'm using node.js v4.2.4 and https://www.promisejs.org/
This should be pretty easy I think...I need to do multiple blocks of async in a specific order, and one of the middle blocks will be looping through an array of HTTP GETs.
//New Promise = asyncblock1 - FTP List, resolve the returned list array
//.then(asynchblock2(list)) - loop through list array and HTTP GET needed files
//.then(asynchblock3(list)) - update local log
I tried creating a new Promise, resolving it, passing the list to the .then, doing the GET loop, then the file update. I tried using a nested promise.all inside asynchblock2, but it's actually going in reverse order, 3, 2, and 1 due to the timing of those events. Thanks for any help.
EDIT: Ok, this is the pattern that I'm using which works, I just need a GET loop in the middle one now.
var p = new Promise((resolve, reject) => {
setTimeout(() => {
console.log('2 sec');
resolve(1);
},
2000);
}).then(() => {
return new Promise((resolve) => {
setTimeout(() => {
console.log('1.5 sec');
// instead of this section, here I'd like to do something like:
// for(var i = 0; i < dynamicarray.length; i++){
// globalvar[i] = ftpclient.getfile(dynamicarray[i])
// }
// after this loop is done, resolve
resolve(1);
},
1500);
});
}).then(() => {
return new Promise((resolve) => {
setTimeout(() => {
console.log('1 sec');
resolve(1);
},
1000);
});
});
EDIT Here is the almost working code!
var pORecAlert = (function(){
var pa;
var newans = [];
var anstodownload = [];
var anfound = false;//anfound in log file
var nexttab;
var lastchar;
var po;
var fnar = [];
var antext = '';
//-->> This section works fine; it's just creating a JSON object from a local file
try{
console.log('trying');
porfile = fs.readFileSync('an_record_files.json', 'utf8');
if(porfile == null || porfile == ''){
console.log('No data in log file - uploaded_files_data.json being initialized!');
plogObj = [];
}
else{
plogObj = JSON.parse(porfile);
}
}
catch(jpfp){
console.log('Error parsing log file for PO Receiving Alert: ' + jpfp);
return endPORecAlertProgram();
};
if((typeof plogObj) === 'object'){
console.log('an_record_files.json log file found and parsed for PO Receiving Alert!');
}
else{
return mkError(ferror, 'pORecAlert');
};
//finish creating JSON Object
pa = new Client();
pa.connect(ftpoptions);
console.log('FTP Connection for FTP Check Acknowledgement begun...');
pa.on('greeting', function(msg){
console.log('FTP Received Greeting from Server for ftpCheckAcknowledgement: ' + msg);
});
pa.on('ready', function(){
console.log('on ready');
//START PROMISE LIST
var listpromise = new Promise((reslp, rejlp) => {
pa.list('/public_html/test/out', false, (cerr, clist) => {
if(cerr){
return mkError(ferror, 'pORecAlert');
}
else{
console.log('Resolving clist');
reslp(clist);
}
});
});
listpromise.then((reclist) => {
ftpplist:
for(var pcl = 0; pcl < reclist.length; pcl++){
console.log('reclist iteration: ' + pcl);
console.log('checking name: ', reclist[pcl].name);
if(reclist[pcl].name.substring(0, 2) !== 'AN'){
console.log('Not AN - skipping');
continue ftpplist;
}
else{//found an AN
for(var plc = 0; plc < plogObj.length; plc++){
if(reclist[pcl].name === plogObj[plc].anname){
//console.log('Found reclist[pcl].name in local log');
anfound = true;
};
};
if(anfound === false){
console.log('Found AN file to download: ', reclist[pcl].name);
anstodownload.push(reclist[pcl].name);
};
};
};
console.log('anstodownload array:');
console.dir(anstodownload);
return anstodownload;
}).then((fnar) => {
//for simplicity/transparency, here is the array being overwritten
fnar = new Array('AN_17650_37411.699.txt', 'AN_17650_37411.700', 'AN_17650_37411.701', 'AN_17650_37411.702.txt', 'AN_17650_37411.801', 'AN_17650_37411.802.txt');
return Promise.all(fnar.map((gfname) => {
var nsalertnames = [];
console.log('Getting: ', gfname);
debugger;
pa.get(('/public_html/test/out/' + gfname), function(err, anstream){//THE PROBLEM IS THAT THIS GET GETS TRIGGERED AN EXTRA TIME FOR EVERY OTHER FILE!!!
antext = '';
console.log('Get begun for: ', gfname);
debugger;
if(err){
ferror.nsrest_trace = 'Error - could not download new AN file!';
ferror.details = err;
console.log('Error - could not download new AN file!');
console.log('************************* Exiting *************************')
logError(ferror, gfname);
}
else{
// anstream.on('data', (anchunk) => {
// console.log('Receiving data for: ', gfname);
// antext += anchunk;
// });
// anstream.on('end', () => {
// console.log('GET end for: ', gfname);
// //console.log('path to update - gfname ', gfname, '|| end text.');
// fs.appendFileSync(path.resolve('test/from', gfname), antext);
// console.log('Appended file');
// return antext;
// });//end end
};
});//get end
}));//end Promise.all and map
}).then((res99) => {
// pa.end();
// return Promise(() => {
console.log('end all. res99: ', res99);
// //res4(1);
// return 1;
// });
});
});
})();
-->> What happens here:
So I added the almost working code. What is happening is that for every other file, an additional Get request gets made (I don't know how it's being triggered), which fails with an "Unable to make data connection".
So for my iteration over this array of 6, there ends up being 9 Get requests. Element 1 gets requested (works and expected), then 2 (works and expected), then 2 again (fails and unexpected/don't know why it was triggered). Then 3 (works and expected), then 4 (works and expected), then 4 again (fails and unexpected) etc
what you need is Promise.all(), sample code for your app:
...
}).then(() => {
return Promise.all(arry.map(item => ftpclient.getFile(item)))
}).then((resultArray) => {
...
So thanks for the help (and the negative votes with no useful direction!)
I actually reached out to a good nodejs programmer and he said that there seemed to be a bug in the ftp module I was using, and even when trying to use a blackbird .map, the quick succession of requests somehow kicked off an error. I ended up using promise-ftp, blackbird, and promiseTaksQueue - the kicker was that I needed interval. Without it the ftp would end up causing a strange illogical error in the ftp module.
You need the async library. Use the async.eachSeries in situations where you need to use asynchronous operations within a loop, then execute a function when all of those are complete. There are many variations depending on the flow you want but this library does it all.
https://github.com/caolan/async
async.each(theArrayToLoop, function(item, callback) {
// Perform async operation on item here.
doSomethingAsync(item).then(function(){
callback();
})
}, function(err){
//All your async calls are finished continue along here
});
I am developing an app in Parse and I'm trying to understand promises. I'm not finding very many working examples other than the very simple ones here: https://parse.com/docs/js/guide.
I'm querying the _User table. Then I loop through the users in an _.each loop. I'm running 2 cloud functions inside the loop for each iteration. At what point do I create the promise? Do I create one for each cloud function success within the loop? Or do I push each success return value onto an array and make that the promise value outside of the loop? I've tried both but I can't figure out the correct syntax to do either, it seems.
I'll break it down in pseudo-code because that may be easier than actual code:
var query = new Parse.Query(Parse.User);
query.find().then(function(users){
loop through each user in an _.each loop and run a cloud function for each that returns a number.
If the number > 0, then I push their username onto array1.
Then I run a 2nd cloud function on the user (still within the _.each loop) that returns a number.
If the number > 0, then I push their username onto array2.
}).then(function(promisesArray){
// I would like "promisesArray" to either be the 2 arrays created in the preceding section, or a concatenation of them.
// Ultimately, I need a list of usernames here. Specifically, the users who had positive number values from the cloud functions in the preceding section
concatenate the 2 arrays, if they're not already concatenated
remove duplicates
send push notifications to the users in the array
});
Questions:
- At what point do I create & return promises & what syntax should I use for that?
- Should .then(function(promisesArray){ be .when(function(promisesArray){ (when instead of then)?
Thank you both for your ideas! This is what ultimately worked:
var query = new Parse.Query(Parse.User);
query.find().then(function(users){
var allPromises = [];
var promise1, promise2;
_.each(users, function(user){
if(user.get("myvalue") != "undefined" && user.get("myvalue") != ""){
promise1 = Parse.Cloud.run("getBatch1", {param1: param1value, param2: param2value})
.then(function(numResult){
if(Number(numResult) > 0){
return Parse.Promise.as(user.getUsername());
}
});
}
allPromises.push(promise1);
if(user.get("anothervalue")==true){
promise2 = Parse.Cloud.run("getBatch2", {param1: param1value, param2: param2value})
.then(function(numResult2){
if(Number(numResult2) > 0){
return Parse.Promise.as(user.getUsername());
}
});
}
allPromises.push(promise2);
});
// Return when all promises have succeeded.
return Parse.Promise.when(allPromises);
}).then(function(){
var allPushes = [];
_.each(arguments, function(pushUser){
// Only add the user to the push array if it's a valid user & not already there.
if(pushUser != null && allPushes.indexOf(pushUser) === -1){
allPushes.push(pushUser);
}
});
// Send pushes to users who got new leads.
if(allPushes.length > 0){
Parse.Push.send({
channels: allPushes,
data: {
alert: "You have new leads."
}
}, {
success: function () {
response.success("Leads updated and push notifications sent.");
},
error: function (error) {
console.log(error);
console.error(error);
response.error(error.message);
}
});
}
response.success(JSON.stringify(allPushes));
}, // If the query was not successful, log the error
function(error){
console.log(error);
console.error(error);
response.error(error.message);
});
I'm not familiar with Parse API but I'd do it this way. Of course, I can't test my code so tell me if it works or not:
var query = new Parse.Query(Parse.User);
query.find()
.then(function(users) {
var promises = [];
users.forEach(function(user) {
// the first API call return a promise so let's store it
var promise = cloudFn1(user)
.then(function(result) {
if (result > 0) {
// just a way to say 'ok, the promise is resolved, here's the user name'
return Parse.Promise.as(user.name);
} else {
// return another promise for that second API call
return cloudFn2(user).then(function(res) {
if (result > 0) {
return Parse.Promise.as(user.name);
}
});
}
});
// store this promise for this user
promises.push(promise);
});
// return a promise that will be resolved when all promises for all users are resolved
return Parse.Promise.when(promises);
}).then(function(myUsers) {
// remove duplicates is easy with _
myUsers = _.uniq(myUsers);
// do your push
myUsers.forEach( function(user) {
});
});
First, you need to understand what Promises are. From what I understand of what you're trying to do it should look something like this:
//constructs the Parse Object
var query = new Parse.Query(Parse.User);
//find method returns a Promise
var res = query.find()
//good names will be a Promise of an array of usernames
//whose value is above 0
var goodNames = res
.then(function(data) {
//assumes the find method returns an array of
//objects, one of the properties is username
//we will map over it to create an Array of promises
//with the eventual results of calling the AJAX fn
var numberPromises = data.map(function(obj) {
//wrap the call to the cloud function in a new
//promise
return new Promise(resolve, reject) {
someCloudFn(obj.username, function(err) {
if (err) {
reject(err);
} else {
resolve(num);
}
});
}
};
//Promise.all will take the array of promises of numbers
//and return a promise of an array of results
return [data, Promise.all(numberPromises)];
})
.then(function(arr) {
//we only get here when all of the Promises from the
//cloud function resolve
var data = arr[0];
var numbers = arr[1];
return data
.filter(function(obj, i) {
//filter out the objects whose username number
//is zero or less
return numbers[i] > 0;
})
.map(function(obj) {
//get the username out of the query result obj
return obj.username;
});
})
.catch(function(err) {
console.log(JSON.stringify(err));
});
Now whenever you need to use the list of usernames whose number isn't zero you can call the then method of goodNames and get the result:
goodNames.then(function(listOfNames) {
//do something with the names
});