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get collection of documents with firestore

I was following this example:
var docRef = db.collection("cities").doc("SF");
docRef.get().then(function(doc) {
if (doc.exists) {
console.log("Document data:", doc.data());
// this is not working
const people = doc.collection("people");
} else {
// doc.data() will be undefined in this case
console.log("No such document!");
}
}).catch(function(error) {
console.log("Error getting document:", error);
});
I want to return an array of people within the city of SF.
According to https://firebase.google.com/docs/database/web/structure-data
when you fetch data at a location in your database, you also retrieve all of its child nodes.
but I can´t find the right to return the collection within a doc (without making a new query)

In Firestore when you retrieve the data, you retrieve all the fields inside a document. If you want to retrieve data from another document or from subcollection then you need to do a different query.

Cloud Firestore can not find custom document id

This function is returning false if i try to get the custom document id.
It is only returning true when I enter document id on the firebase console.
checkDot() {
this.db.firestore.collection(this.DOT).doc(this.DOT).get()
.then( doc => {
console.log('Data is ', doc.exists);
if (doc.exists) {
// this.isDotExist = true;
console.log(doc, 'Colection exists');
}
else {
// new Account Create
console.log('Colection doos not exist');
this.presentConfirm();
}
});
This function stores user input in the database
async createNewAccount() {
// Binding data from user input
const { Company, Fname, Email, Password } = this;
try {
// creating user account
const res = await this.afAuth.auth.createUserWithEmailAndPassword(Email, Password).then(cred => {
// DOT value passed by another page, others from user input
this.db.collection(this.DOT).doc(this.DOT).collection(Company).doc(Fname).set({ Name: Fname });
});
this.showAlert('Succes', 'You have successfully registered!');
this.route.navigate(['']);
console.log(res);
} catch (err) {
this.showAlert('Error', err.message);
// console.dir(err);
}
}

As you can check in this question from the Community Query Firebase Firestore documents by the ID, there is a special method that you can use query via documentId. The method is this: 'FieldPath.documentId()'
Another reference is the official documentation Execute Query, where you can find the following example of code that you can use as a start point, to return documents via ID.
db.collection("collection").where("document", "==", true)
.get()
.then(function(querySnapshot) {
querySnapshot.forEach(function(doc) {
// doc.data() is never undefined for query doc snapshots
console.log(doc.id, " => ", doc.data());
});
})
.catch(function(error) {
console.log("Error getting documents: ", error);
});
Besides that, there is the below question from the Community with more information and examples, related to a similar to yours, that might help you.
How to perform collection group query using document ID in Cloud Firestore
Let me know if the information helped you!

Firestore WEB trigger event

I'm running my db to verify if "id" is already in use, if not, i can do my register, else, i cant user this id and i have to try another.
code:
db.collection("places").get().then(function (querySnapshot) {
querySnapshot.forEach(function (doc) {
// console.log(doc.id)
db.collection("places").doc(doc.id).collection("Local").where("id", "==", id_user)
.get()
.then(function (querySnapshot) {
querySnapshot.forEach(function (doc2) {
//cpnj is already registred
if (doc2.exists) {
console.log("id already exist")
document.getElementById("preloader").style.display = "none";
alert("id in use, try another id");
} else{
//register the user
}
});
})
.catch(function (error) {
console.log("Error getting documents: ", error);
});
});
});
The problem is when id doesn't exist, the "else" inside the function is not "actived" because the Firebase condition".where("id", "==", id_user)" doesn't exist, so the query is not done.
How can i trigger this and after check that the "id" is not in use and proceed with registration?

Within a loop over a query snapshot, the document will always exist. If there are no results, the query snapshot will be empty and it'll right now simply not enter your forEach loop.
What you're looking for is whether the query snapshot has any results, which you can do with:
if (querySnapshot.empty) {
//register the user
} else{
console.log("id already exist")
document.getElementById("preloader").style.display = "none";
alert("id in use, try another id");
}

Retrieveing data from document of a collection in firestore database with document ID

I want to make a chat application with chat room by implementing firebase friendly chat app. I want to get all the information from "rooma" documentid of message collection. But i am not able to get the information from the document with ID "rooma" but i can access all the information from "message" collection.
my code is:
function loadMessages() {
// Create the query to load the last 12 messages and listen for new ones.
var query = firebase.firestore()
.collection('messages').where(firebase.firestore.FieldPath.documentId(), '==', 'rooma').get()
.orderBy('timestamp', 'desc')
.limit(12);
// Start listening to the query.
query.onSnapshot(function(snapshot) {
snapshot.docChanges().forEach(function(change) {
if (change.type === 'removed') {
deleteMessage(change.doc.id);
} else {
var message = change.doc.data();
displayMessage(change.doc.id, message.timestamp, message.name,
message.text, message.profilePicUrl, message.imageUrl);
}
});
});
}
my database structure is:
Imgur

If you want to get the data of "the document with ID 'rooma'", just do as follows, according to the documentation:
var docRef = db.collection("messages").doc("rooma");
docRef.get().then(function(doc) {
if (doc.exists) {
console.log("Document data:", doc.data());
} else {
// doc.data() will be undefined in this case
console.log("No such document!");
}
}).catch(function(error) {
console.log("Error getting document:", error);
});
If you want to use onSnapshot(), in order to "listen to a document", you just have to do as follows, according to the documentation:
var docRef = db.collection("messages").doc("rooma");
docRef.onSnapshot(function(doc) {
console.log("Current data: ", doc.data());
});

Firestore how to get keys from firestore document

Using below query, I can get the document and doc.data().name to get the value for the key 'name'. I would like to get all the keys in that document. How can I get that?
var docRef = db.collection("cities").doc("SF");
docRef.get().then(function(doc) {
if (doc.exists) {
console.log("Document data:", doc.data());
//**I want to get all keys in the document here.**
} else {
// doc.data() will be undefined in this case
console.log("No such document!");
}
}).catch(function(error) {
console.log("Error getting document:", error);
});

Based on my example from this answer, you can do:
docRef.get().then(function(doc) {
if (doc.exists) {
let json = doc.data();
console.log("Document data:", json);
console.log("Document keys:", Object.keys(json));
Object.keys(json).forEach((name) => {
console.log(name, json[name]);
});
} else {
// doc.data() will be undefined in this case
console.log("No such document!");
}
}).catch(function(error) {
console.log("Error getting document:", error);
});

In firebase, If you want to access the value of a key in a document inside your collection. Let's say key "name" or "email". Use the code below:
searchSnapshot.docs[index]["name"].data()
searchSnapshot.docs[index]["email"].data()
Note: I used search box here, you might have a different plugin to implement.