CODEWITHSUNDEEP
react-nativegoogle-cloud-firestore
honor
honor

Reputation: 8098

firestore how to check if new documents added matching a particular query

As I know that, instead of get() I can use onSapshot() for my queries and listen to the changes(additions, deletions, modifications) for that query. But when there are changes, onSnaphot() returns multiple full documents whether modified, deleted or added (a new snapshot). What I want to do is, to check if new documents have been added matching my query and show a notification to the user that there are new records available, and only when a button is clicked, they should be able to fetch and see the new records. I don't want to fetch from the firestore whole sets of documents when there are changes. I just want to know about those changes and fetch on demand. And fetch only the added ones.

How can I do that? Any ideas?

By the way, I am using react-native for my app.

P.S. - I know, I can run the query periodically and check if the id of the first item in the new query matches the first item id in the previous query, and so I can detect the added records and show my notification/button. But I am looking for a more elegant solution. I think the notification should be triggered from the backend instead of polling the backend periodically.

P.S. 2 - Using cloud functions would not seem to be a logical option since these queries will be different for each user of my app. Which would require running thousands of functions (hopefully more) on the firestore. Or would it?

Thanks!

Upvotes: 0

Views: 785

Answers (1)

Frank van Puffelen
Frank van Puffelen

Reputation: 598668

There is no way in the Firestore API to get notified about changes to a query without actually retrieving the changed documents. But you can of course show just a notification to the user when your onSnapshot callback gets called, and then only show the actual data from those documents when the user chooses to refresh the UI.

On a second note, when you use a snapshot listener the Firestore client will only retrieve the modified documents on additional callbacks.

Say you attach a listener for a query that matches 10 documents. On the first onSnapshot callback, you will get 10 documents and will be charged for 10 document reads. Now say that one of the documents changes. When your onSnapshot callback gets invoked for this, you will see 10 documents again, but will be charged only 1 read - for the document that was changed.

If you only want to process the changes, have a look at the documentation on viewing changes between snapshots, which contains a good example of how to do this with the docChanges() method.

Upvotes: 2

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