How to automatically update same field in different collections in Firestore - firebase

Question

I am using Cloud Firestore as my database and I have collections of users where are stored basic information about user such as id, name, last name, email, company id.
Also I have collection of companies and in each company I have collection of tasks.
In each task I have one user assigned from collections of users (user data is replicated, so I have same data for that user as in collection users)
The problem is when I update user (change name or email...) from collection users because data is replicated that data is not changed in collection of tasks for that specific user.
Is there any way that using firestore when user from collection users is updated to automatically update it in collection of tasks?

Answer 1

This is quite a standard case in NoSQL databases, where we often denormalize data and need to keep these data in sync.
Basically you have two possible main approaches:
#1 Update from the client
When you update the "user" document, update at the same time the other documents (i.e. "tasks") which contain the user's details. You should use a batched write to do so: A batch of writes completes atomically and can write to multiple documents.
Something along the following lines:
// Get a new write batch
var batch = db.batch();
var userRef = db.collection('users').doc('...');
batch.update(userRef, {name: '....', foo: '....'});
let userTaskRef = db.collection('companies').doc('...').collection('tasks').doc('taskId1');
batch.update(userTaskRef, {name: '....'});
userTaskRef = db.collection('companies').doc('...').collection('tasks').doc('taskId2');
batch.update(userTaskRef, {name: '....'});
// ...
// Commit the batch
batch.commit().then(function () {
// ...
});
Note that you need to know which are "the other ("tasks") documents which contain the user's details": you may need to do a query to get these documents (and their DocumentReferences).
#2 Update in the back-end via a Cloud Function
Write and deploy a Cloud Function that is triggered when any "user" document is updated and which takes the value of this "user" document and update the "tasks" documents which contain the user's details.
Like for the first approach, you also need, in this case, to know which are "the other ("tasks") documents which contain the user's details.
Following your comment ("Is there any option to reference to another table or put foreign key?") here is a Cloud Function that will update all the ("tasks") documents that have their DocumentReference contained in a dedicated Array field taskRefs in the "user" doc. The Array members are of data type Reference.
exports.updateUser = functions.firestore
.document('users/{userId}')
.onUpdate((change, context) => {
const newValue = change.after.data();
const name = newValue.name;
const taskRefs = newValue.taskRefs;
const promises = taskRefs.map(ref => { ref.update({ name: name, foo: "bar" }) });
return Promise.all(promises);
});
You would most probably set the value of this taskRefs field in the "user" doc from your frontend. Something along the following lines with the JS SDK:
const db = firebase.firestore();
db.collection('users').doc('...').set({
field1: "foo",
field2: "bar",
taskRefs: [ // < = This is an Array of References
db.collection('tasks').doc('....'),
db.collection('tasks').doc('....')]
});