child-count

Tracking the number of elements in a list

This template shows how to keep track of the number of elements in a Firebase Database list. For instance this can be useful to keep track of the number of "likes" or "followers" of something shared on a social platform.

Functions Code

See file functions/index.js for the code.

This is done by updating a likes_count property on the parent of the list node which is tracked.

This counting is done in two cases:

1. When a like is added or deleted, the likes_count is incremented or decremented.
2. When the likes_count is deleted, all likes are recounted.

The dependencies are listed in functions/package.json.

Sample Database Structure

As an example we'll be using the database structure shown below. It keeps tracks of the list of users who liked a post and the count of these likes:

/functions-project-12345
    /posts
        /key-123456
            likes_count: 32
            /likes 
                user123456: true
                user456789: true
                user786245: true
                ...