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Delete a batch of docs using admin SDK and callable cloud function in most similar way to client SDK?

I have an array of docs ids that I want to delete in using a cloud function, my code looks like the following :
//If the user decieds on deleting his account forever we need to make sure we wont have any thing left inside of db after this !!
// incoming payload array of 3 docs
data = {array : ['a302-5e9c8ae97b3b','92c8d309-090d','a302-5e932c8ae97b3b']}
export const deleteClients = functions.https.onCall(async (data, context) => {
try {
// declare batch
const batch = db.batch();
// set
data.arr.forEach((doc: string) => {
batch.delete(db.collection('Data'), doc);
});
// commit
await batch.commit();
} catch (e) {
console.log(e);
}
return null;
});
I am getting a syntax error on batch.delete how to pass the right arguments in to the batch delete to reference that doc I want to submit for deletion before commit ?

Delete takes a single param, the doc ref of the doc to be deleted.
data.arr.forEach((docId: string) => {
batch.delete(doc(db, "Data", docId));
});

There are several errors in your code:
data.arr.forEach() cannot work wince your data object contains one element with the key array and not the key arr.
You are mixing up the syntax of the JS SDK v9 and the Admin SDK. See the write batch Admin SDK syntax here.
You need to send back some data to the client when all the asynchronous work is complete, to correctly terminate your CF.
You do return null; AFTER the try/catch block: this means that, in most of the cases, your Cloud Function will be terminated before asynchronous work is complete (see the link above)
So the following should do the trick (untested):
const db = admin.firestore();
const data = {array : ['a302-5e9c8ae97b3b','92c8d309-090d','a302-5e932c8ae97b3b']};
export const deleteClients = functions.https.onCall(async (data, context) => {
try {
const batch = db.batch();
const parentCollection = db.collection('Data')
data.array.forEach((docId) => {
batch.delete(parentCollection.doc(docId));
});
// commit
await batch.commit();
return {result: 'success'} // IMPORTANT, see explanations above
} catch (e) {
console.log(e);
// IMPORTANT See https://firebase.google.com/docs/functions/callable#handle_errors
}
});

Angular: returning a value from onValue() in firebase realtime database

I would like to return the "User" object.
Got error message:
Variable 'user' is used before being assigned.ts(2454)
I tried to use async / await but I can't assign await to "return user" at the end of the code or user= await snapshot.val() because it is located on onValue() scope.
getLoggedInUser(id: string): User {
const db = getDatabase();
var user: User;
onValue(ref(db, '/users/' + id), (snapshot) => {
user = snapshot.val();
// ...
}, {
onlyOnce: true
});
return user;
}

When you call onValue you get the current value from that path in the database, and then also get all updates to that value. Since your callback may be called multiple times, there is no way to return a single value.
If you want to just get the value once and return it, you'll want to use get instead of onValue. Then you can also use async/await.
async getLoggedInUser(id: string): Promise<User> {
const db = getDatabase();
var user: User;
const snapshot = await get(ref(db, '/users/' + id))
user = snapshot.val();
return user;
}

I am actually having a similar issue, although I try to fetch data with paging logic.
We do have thousands of records and to render them nicely (10 - 25 per page) would be the best option anyhow.
const dbRef = query(ref(database, folder), orderByChild(field), startAt(start), limitToLast(limit))
return onValue(dbRef, (snapshot) => {
const values = Object.values(snapshot.val());
return {data: values, total: values.length, page: page}
})
I can see the values inside the onValue, but it seems not to return the value at all. I'm not sure where to go here, the documentation on that is not completely clear to me (a beginner as a developer).

Error while deleting a value of element in mongoDB array using filter function?

I tried to find the solutions over here but unable to get success while using $pull as the array values I have does not contain `mongo_id'.
So the scenario is that , I am trying to delete the specific comment of the particular user which I am passing through query params. M
My mongo data looks like this:
Now I am making API Delete request like this : http://localhost:8000/api/articles/learn-react/delete-comment?q=1 on my localhost .
ANd finally my code looks like this:
import express from "express";
import bodyParser from "body-parser";
import { MongoClient } from "MongoDB";
const withDB = async (operations, res) => {
try {
const client = await MongoClient.connect(
"mongodb://localhost:27017",
{ useNewUrlParser: true },
{ useUnifiedTopology: true }
);
const db = client.db("my-blog");
await operations(db);
client.close();
} catch (error) {
res.status(500).json({ message: "Error connecting to db", error });
}
};
app.delete("/api/articles/:name/delete-comment", (req, res) => {
const articleName = req.params.name;
const commentIndex = req.query.q;
withDB(async(db) => {
try{
const articleInfo = await db.collection('articles').findOne({name:articleName});
let articleAllComment = articleInfo.comments;
console.log("before =",articleAllComment)
const commentToBeDeleted = articleInfo.comments[commentIndex];
//console.log(commentToBeDeleted)
// articleAllComment.update({
// $pull: { 'comments':{username: commentToBeDeleted.username }}
// });
articleAllComment = articleAllComment.filter( (item) => item != commentToBeDeleted );
await articleAllComment.save();
console.log("after - ",articleAllComment);
//yaha per index chahiye per kaise milega pta nhi?
//articleInfo.comments = gives artcle comment
res.status(200).send(articleAllComment);
}
catch(err)
{
res.status(500).send("Error occurred")
}
},res);
});
I have used the filter function but it is not showing any error in terminal but also getting 500 status at postman.
Unable to figure out the error?

I believe you'll find a good answer here:
https://stackoverflow.com/a/4588909/9951599
Something to consider...
You can use MongoDB's built-in projection methods to simplify your code.
https://docs.mongodb.com/manual/reference/operator/projection/positional/#mongodb-projection-proj.-
By assigning a "unique ID" to each of your comments, you can find/modify the comment quickly using an update command instead of pulling out the comment by order in the array. This is more efficient, and much simpler. Plus, multiple read/writes at once won't interfere with this logic during busy times, ensuring that you're always deleting the right comment.
Solution #1: The recommended way, with atomic operators
Here is how you can let MongoDB pull it for you if you give each of your comments an ID.
await db.collection('articles').updateOne({ name:articleName },
{
$pull:{ "comments.id":commentID }
});
// Or
await db.collection('articles').updateOne({ name:articleName, "comments.id":commentID },
{
$unset:{ "comments.$":0 }
});
Solution #2 - Not recommended
Alternatively, you could remove it by index:
// I'm using "3" here staticly, put the index of your comment there instead.
db.collection('articles').updateOne({ name:articleName }, {
$unset : { "comments.3":0 }
})
I do not know why your filter is erroring, but I would recommend bypassing the filter altogether and try to utilize MongoDB's atomic system for you.

Firestore get a post title using async await

I am trying to get a post title from firestore but somehow I could not figure out how that could be done using async await.
async getVideo(id) {
var self = this;
const ref = this.$fire.firestore
.collection("posts")
.where("ytid", "==", id)
.orderBy("createdAt", "desc");
try {
let post = await ref.get();
console.log(post.data());
} catch (e) {
console.log(e);
}
}
I tried to console log post.data() but it says post.data() is not a function.
Any help would be appreciated.

When you call ref.get(), you will get a QuerySnapshot object. This object contains zero or more DocumentSnapshot objects that contain the data from the query results. QuerySnapshot does not have a method called data(). You will have to iterate the documents using the provided API to get the DocumentSnapshots:
const qsnapshot = await ref.get();
qsnapshot.forEach(doc => {
const data = doc.data();
console.log(data);
})

You are retrieving multiple documents, so post will be a snapshot of documents which does not have a data() method.
You'll need to iterate through the snapshot to access the individual documents.
See https://firebase.google.com/docs/firestore/query-data/get-data#get_multiple_documents_from_a_collection for a quick guide or https://googleapis.dev/nodejs/firestore/latest/QuerySnapshot.html for a full reference of the QuerySnapshot type.

How to return value of both of the consecutive async functions in JS?

I've recently started with web development, and am a novice in JavaScript.
I'm currently working on a Blog Project and using Firebase as the backend, and Firestore as the Database.
PROJECT-
using the following project structure
Firestore DB ->
-Posts
-post1
-post2
-post3
...
-authors
-author1
-author2
..
-subscribers
...
I'm using this function to retrieve my posts from Firestore.
app.get('/:id', (req, res) => {
const id = req.params.id;
async function getDocument(id) {
const doc = await db.collection('Posts').doc(id).get();
if (!doc.exists) {
console.log('No such document!');
} else {
return doc.data();
}
}
getDocument(id).then(function (data) {
res.render('post',{ articleInfo:data} );
// that send back an object containing post details
})
Now, from the JSON I get from the above function, I want to use the value of "Author" to get the author's details from the another collection(run another async function),
and then send this data along with the data from previous function(used to get post details) together in res.render()
For example
I make a get request for a post and get back it's details. Inside which get the author's name "{..,"author : mike-ross",..} " .
Now, after .then, I use this value to run another async function get this author's JSON from the Authors collection. and pass the result from both the functions together in res.render() to get diplayed on the page.

You could have one async function that does both calls and returns an object with both results:
async function getDocWithDetails (id) {
const doc = await getDocument(id);
const authorInfo = await getAuthorInfo(doc.author);
return {
doc: doc.data(),
authorInfo: doc.data()
}
}
getDocWithDetails(id).then((data) => {
res.render('post', data) // has data.doc and data.authorInfo
});

Just go for it, same way you did the first half :-)
In general (at least at my work projects), it's good practice to setup multiple getters for each collection or one main getter where the collection is a secondary argument.
Here's the second variant with dynamic variant (but the first one is just as valid). Especially if you're not using typescript or flowtype to typecheck what you're passing, then it's more prone to unexpected errors by passing incorrect param, I'm just lazy to write the similar function in the answer twice.
const getDocumentById = async (id, collection) => {
const doc = await db.collection(collection).doc(id).get()
if (!doc.exists) {
throw Error(`Doc with id "${id}" doesn't exist on collection "${collection}"`)
}
return doc.data()
}
Now that we have our generic getter setup, you just need to create a function that fetches both.
As a precursor, I have taken some creative liberties with the answer, since the question is missing some cruicial info about documents.
At the very least (and if you don't you should, it's good firebase practice) I presume you have a link to the authorId inside Posts document.
Posts
-> post
-> id
-> authorId
-> some_other_fields
Authors
-> author
-> id
-> some_other_fields
With the following structure in mind, your answer will look something like this:
const getAuthorByPostId = async (id) => {
try {
const post = await getDocumentById(id, 'Posts')
const { authorId } = post
const author = await getDocumentById(authorId, 'Authors')
// I'm not sure how your res is structured, but could look something like this
res.render('page', { articleInfo: post, authorInfo: author })
} catch (error) {
console.error(error.message)
}
// in case it was unable to fetch data
return null
}