Get last created document in a Firebase Firestore collection

Question

Is there any way to get last created document in Firebase Firestore collection? My requirement is when user signed I have to add a document in a collection named 'history'; When the user signed out I want to update that document with a field called 'signout'; So if i get the lastly added document it is very easy to update. Is there any way to do this?

Solution

Is there any way to get the last created document in Firebase Firestore collection?

Yes, there is! The simplest way to achieve this is to add a date property to each object in your collection, then simply query it according to this new property descending and call limit(1) function. That's it!

As @eyyo mentioned in his comment, here is a concrete example. Assuming that your database schema looks like this:

Firestore-root
  |
  --- history (collection)
        |
        --- docId (document)
             |
             --- date: June 24, 2020 at 6:46:25 PM UTC+3
             |
             --- //Other properties

This is the required query:

this.historyRef = afs.collection<History>('history', ref => ref.orderBy('date', 'desc').limit(1));
this.history = this.historyRef.snapshotChanges().map(actions => {
    return actions.map(a => {
        const data = a.payload.doc.data() as Hisotory;
        const docId = a.payload.doc.id;
        return { docId, ...data };
    });
});

Comments

[pepe]

can you please explain it.?

[Alex Mamo]

Give it a try and keep me posted.

[BluE_MoOn]

The problem with this solution is that you manually have to create a Index for every document it in the Firebase console. Is there any other way to get the latest document inserted ?

[Alex Mamo]

@BluE_MoOn Simply adding a Date property does not require an index. The index is automatically created for you. If you need to query and order, yes, there an index is required.

[Gabriel]

Is the Date property a field in the collection? Can it exist within a map?

[Alex Mamo]

@Max The Date property cannot exist in a collection, only in a document. And yes, the `Date can be added to a Map.

[Daniel]

An example would be very useful!

[Daniel]

Thank you @AlexMamo!

[1x2x3x4x]

Thanks for this, I was looking for something similiar. One question though. Doing ref.orderBy('date', 'desc').limit(1) will be ONE READ or Fireabase will consider you've read the whole collection? @AlexMamo

[Alex Mamo]

@1x2x3x4x Yes, it will be indeed only one read, as your query only one document returns.