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Firebase firestore: how to query relevant documents and then update each of them

I am developing a web app on Firebase/firestore, in which users can sign in and write their own posts. The data are stored in the following way:
-User information are stored as under collection('user').doc('uid').
-Information about posts the user has written are stored in collection('post').doc('postid'), and the doc has 'userinfo' and 'uid' fields. The 'userinfo' field contains exact copy of what is stored in 'uid' doc, just in object format.
Here are the operations that I want to do:
When the user changes the data, the changes are reflected in the document.
Look for the all the posts that the user has written based on 'uid' data, and then update userinfo in those data.
The last part is tricky for me. The Firebase documentations cover situations where the references are pretty much static, i.e. you know the exact path to write/update. What I am trying to do is look for a set of documents that is not necessarily static, and then update each of them.
Here is the code I wrote for this effort. The first part works without any problem. Of course, the second part doesn't work. :) What would be the code to do the do the second part?
const update = () => {
//This part is for updating user information. This works without any problem.
firebase.firestore().collection('user').doc(user.uid).update({
username: username1,
nickname: nickname1,
intro: intro1
})
.then(()=>{
//This part is for updating all of the document that the user has written based on 'uid' value. This doesn't work.
//Below code is probably way off, but it shows where I am going and what I am trying to do.
firebase.firestore().collection('post').where('uid','==',user.uid).get()
.then((querysnapshot)=>{
querysnapshot.forEach((doc)=>{
let ref=firebase.firestore().collection('post').doc(doc.id);
ref.update({
userinfo: {nickname:nickname1,username:username1,intro:intro1}
})
})
})
}).then(()=>{
alert("Successfully updated!");
window.location.href='/'+username1;
}).catch((error)=>{
alert("Error!");
})
}
Thanks a lot in advance!

What's the error that you get running this code? It seems on the right track for me.
But despite that, here are some suggestions to deal with this kind of update:
Don't do the second part on the client side, do it on the server side with a Firestore Trigger (create a onUpdate trigger in the user collection in your case): https://firebase.google.com/docs/functions/firestore-events.
The problem of doing in the client side, is because if the user closes the page/browser or the site goes offline in the middle of the update, you will have inconsistent data.
You don't need to recreate the DocumentReference after getting the query result, the docs returned already have a .ref that you can call .ref.update() directly.
EDIT: If you want to keep your original code (updating on client side), the problem of the navigation occurring before all the updates to conclude is because ref.update() returns a promise.
So the update queue is asynchronous being performed on database when the client navigates away.
To solve this, I would use a Promise.all() to wait all updates being completed.
firebase.firestore().collection('post').where('uid','==',user.uid).get()
.then((querysnapshot)=>{
const promises = [];
querysnapshot.forEach((doc)=>{
promises.push(doc.ref.update({
userinfo: {nickname:nickname1,username:username1,intro:intro1}
});
});
Promise.all(promises).then(()=>{window.location.href='/'+username1;});
});
Or using the await syntax (I think it's easier to maintain and understand):
const querysnapshot = await firebase.firestore().collection('post').where('uid','==',user.uid).get();
const promises = [];
querysnapshot.forEach((doc)=>{
promises.push(doc.ref.update({
userinfo: {nickname:nickname1,username:username1,intro:intro1}
});
});
await Promise.all(promises);
window.location.href='/'+username1;

Redirect to new Mongo Saved ID after Express POST?

In my POST request, I'm saving a new document into my mongo database. After the database is saved, can I do a res.redirect to that exact document ID?? I'm unsure of how to do this. I can't find any tutorials, documentation, or stackoverflow questions that seem to answer exactly what I'm looking for.
Can I do something like this? Where the :id is the Id of the document I just saved in mongoose/mongo?
newItem.save().then(res.redirect('/results/:id');
I expect the user to submit a post request. I'm saving the information into a mongo document through mongoose. Then after saving it I'd like to redirect to a new URL with the ID of the saved item on that page.

Of course you can.
The save() method can accept a callback so you can get the _id field of the saved document.
One way of do it would be:
newItem.save((err, itemSaved) => {
if(err) {
next(err);
}
const itemId = itemSaved._id;
res.redirect('/results/' + itemId);
});
Hopefully, this will solve your problem.
P.S.
There's no need to use a colon on redirect's path. Beware with that, 'cause using it will give you a Cast Error.

MeteorJS - No user system, how to filter data at the client end?

The title might sound strange, but I have a website that will query some data in a Mongo collection. However, there is no user system (no logins, etc). Everyone is an anonymouse user.
The issue is that I need to query some data on the Mongo collection based on the input text boxes the user gives. Hence I cannot use this.userId to insert a row of specifications, and the server end reads this specifications, and sends the data to the client.
Hence:
// Code ran at the server
if (Meteor.isServer)
{
Meteor.publish("comments", function ()
{
return comments.find();
});
}
// Code ran at the client
if (Meteor.isClient)
{
Template.body.helpers
(
{
comments: function ()
{
return comments.find()
// Add code to try to parse out the data that we don't want here
}
}
);
}
It seems possible that at the user end I filter some data based on some user input. However, it seems that if I use return comments.find() the server will be sending a lot of data to the client, then the client would take the job of cleaning the data.
By a lot of data, there shouldn't be much (10,000 rows), but let's assume that there are a million rows, what should I do?
I'm very new to MeteorJS, just completed the tutorial, any advice is appreciated!

My advice is to read the docs, in particular the section on Publish and Subscribe.
By changing the signature of your publish function above to one that takes an argument, you can filter the collection on the server, and limiting the data transferred to what is required.
Meteor.publish("comments", function (postId)
{
return comments.find({post_id: postId});
});
Then on the client you will need a subscribe call that passes a value for the argument.
Meteor.subscribe("comments", postId)
Ensure you have removed the autopublish package, or it will ignore this filtering.

Ionic Push User identification issue

I'm having this issue where I register for Push using $ionicPush.register() But I'm not doing user identification at any point using $ionicUser(like the docs suggest). So, I'm only calling $ionicPush.register() and I wait for that promise to resolve and I'm storing the device_token on my server, eg.
$ionicPush.register({
onNotification: function(notification) {
//....
}
}).then(function(deviceToken) {
//Save device-token to my server
UserService.saveIosDeviceToken(user.id, deviceToken)
.then(function(user) {
return user;
})
.catch(function(error) {
console.log(error);
});
});
I have noticed that regardless of calling $ionicUser.identify(...) or not, an $ionicUser will be created (which you can see in the Dashboard). Now the issue that I'm having is that I'm not always getting a device token. ie. I end up with some(not all) Ionic Users with no device tokens (therefore no device token I can store on my server), eg.
Do you guys know what's going on? I'm reading the FAQ here and it says: > "If you are using $ionicPush.register() without passing a user object, you should make sure you are waiting for the $ionicPush.identify() promise to complete." -- Could this be the likely cause? and How do I pass a user to $ionicPush.register()?
Let me know what you guys think, I really need to know what I'm doing wrong.
Regards,
-J

Parse iOS SDK: Understanding Cloud Code

Scenario = I am slowly but surely wrapping my head around what is going on with Parse's cloud code features. I just need some help from those who would like to answer some short, relatively simple questions about what is going on in some sample cloud code functions.
The code I will use in this example is below
1) cloud code
Parse.Cloud.define('editUser', function(request, response) {
var userId = request.params.userId,
newColText = request.params.newColText;
var User = Parse.Object.extend('_User'),
user = new User({ objectId: userId });
user.set('new_col', newColText);
Parse.Cloud.useMasterKey();
user.save().then(function(user) {
response.success(user);
}, function(error) {
response.error(error)
});
});
2) called from iOS
[PFCloud callFunction:#"editUser" withParameters:#{
#"userId": #"someuseridhere",
#"newColText": #"new text!"
}];
This code was taken from here
Question 1 =
(request, response)
I am confused by what this is. Is this like typecasting in iOS where I am saying (in the iOS call) I want to pass an NSString into this function ("userId") and inside the cloud code function I'm going to call it "request"? Is that what's going on here?
Question 2 =
Parse.Object.extend('_User')
Is this grabbing the "User" class from the Parse database so that a "PFObject" of sorts can update it by creating a new "user" in the line below it?
Is this like a...
PFObject *userObject = [PFObject objectWithClassName:#"User"]?
Question 3 =
user.set('new_col', newColText)
This obviously 'sets' the values to be saved to the PFUser (~I think). I know that the "newColText" variable is the text that is to be set - but what is 'new_col'? Only thing I can think of is that this sets the name of a new column in the database of whatever type is being passed through the "request"?
Is this like a...
[[PFUser currentUser] setObject: forKey:]
Question 4 =
Parse.Cloud.useMasterKey()
Without getting too technical, is this basically all I have to type before I can edit a "User" object from another User?
Question 5 =
user.save().then(function(user) {
response.success(user);
}
Is this like a...
[user saveInBackgroundWithBlock:]?
and if so, is
function(error) {
response.error(error)
just setting what happens if there is an error in the saveInBackgroundWithBlock?
Please keep in mind, I know iOS - not JavaScript. So try to be as descriptive as possible to someone who understands the Apple realm.

Here's my take on your questions:
The request parameter is for you to access everything that is part of the request/call to your cloud function, it includes the parameters passed (request.params), the User that is authenticated on the client (request.user) and some other things you can learn about in the documentation. The response is for you to send information back to the calling code, you generally call response.success() or response.error() with an optional string/object/etc that gets included in the response, again documentation here.
That's a way of creating an instance of a User, which because it is a special internal class is named _User instead, same with _Role and _Installation. It is creating an instance of the user with an ID, not creating a new one (which wouldn't have an ID until saved). When you create an object this way you can "patch" it by just changing the properties you want updated.
Again, look at the documentation or an example, the first parameter is the column name (it will be created if it doesn't exist), the second value is what you want that column set to.
You have to do Parse.Cloud.useMasterKey() when you need to do something that the user logged into the client doesn't have permission to do. It means "ignore all security, I know what I'm doing".
You're seeing a promise chain, each step in the chain allows you to pass in a "success" handler and an optional "error" handler. There is some great documentation. It is super handy when you want to do a couple of things in order, e.g.
Sample code:
var post = new Parse.Object('Post');
var comment = new Parse.Object('Comment');
// assume we set a bunch of properties on the post and comment here
post.save().then(function() {
// we know the post is saved, so now we can reference it from our comment
comment.set('post', post);
// return the comment save promise, so we can keep chaining
return comment.save();
}).then(function() {
// success!
response.success();
}, function(error) {
// uh oh!
// this catches errors anywhere in the chain
response.error(error);
});

I'm pretty much at the same place as you are, but here are my thoughts:
No, these are the parameters received by the function. When something calls the editUser cloud function, you'll have those two objects to use: request & response. The request is basically what the iOS device sent to the server, and response is what the server will send to the iOS device.
Not quite that. It's like creating a subclass of _User.
Think of Parse objects types as a database table and it's instances as rows. The set will set (derp) the value of 'newColText' to the attribute/column 'new_col'.
Not sure, never used that function as I don't handle User objects. But might be that.
Pretty much that. But it's more sort of like (pseudo-code, mixing JS with Obj-C):
[user saveInBackgroundWithBlock:^(BOOL succeeded, NSError *error){
if(error){
response.error(error); // mark the function as failed and return the error object to the iOS device
}
else{
response.success(user); // mark the function call as successful and return the user object to the iOS device
}
}];