Using Firestore in a Google App Engine project - google-app-engine

Question

I want to access Firestore's real-time database inside of my Google App Engine project as an additional database.
What is the best way to write to Firestore from a Google App Engine backend? Would using the Firestore Rest API be decent? Or is there a better method?
How would authentication work between the two projects? Since as far as I understand a Google App Engine project and Firestore project are two separate things.

Answer 1

Yes, the best practice is to use the Firestore Rest API.
Concerning the authentication, the app engine service has its default service account which you can find on the app engine page.
Simply grant permissions to this service account on the project B to access & write firestore and the Lib SDK will smoothly handle everything!
Which language are you using ? So I could edit my answer with a demo code
Edit 1:
You may misunderstand the concept of projects. A project is an envelope where you can use services. IN this example: you can have a single GCP project containing your firestore and your App Engine.
Edit 2:
As I thought, there's a code sample on the Google demo repo. Check this out !
https://github.com/GoogleCloudPlatform/java-docs-samples/tree/master/firestore

Answer 2

The best way to access Google Cloud Firestore is using its client libraries (rather than the REST API). I mean, you could use the REST API, there's nothing wrong w/that at all, however it generally involves more coding on your part whereas the client library does more of the heavy-lifting.
With the client library, setting up an API client is a 1-liner, then accessing it is straightforward. Here's a code snippet for a simple web app that tracks all website visits just to show you basic usage (works on 2.x & 3.x):
'fs_visits.py -- Cloud Firestore sample Python snippet for web visit registry'
from __future__ import print_function
from datetime import datetime
from google.cloud import firestore
def store_visit(timestamp):
visits = fs_client.collection('visitX')
visits.add({'timestamp': timestamp})
def fetch_visits(limit):
visits = fs_client.collection('visitX')
return visits.order_by(u'timestamp',
direction=firestore.Query.DESCENDING).limit(limit).stream()
TOP = 10 # limit to 10 results
fs_client = firestore.Client() # create Cloud Firestore client
if __name__ == '__main__':
print('** Adding another visit')
store_visit(datetime.now()) # store a "visit" object
print('** Last %d visits' % TOP)
times = fetch_visits(TOP) # fetch most recent "visits"
for obj in times:
print('-', obj.to_dict()['timestamp'])
Here's the sample output I got when I ran it:
$ python fs-snip.py
** Adding another visit
** Last 10 visits
- 2020-03-23 09:14:09.742027+00:00
- 2020-03-11 01:06:47.103570+00:00
- 2020-03-11 01:03:29.487141+00:00
- 2020-03-11 01:03:16.583822+00:00
- 2020-03-11 01:02:35.844559+00:00
- 2020-03-11 00:59:51.939175+00:00
- 2020-03-11 00:59:39.874525+00:00
- 2020-03-11 00:58:51.127166+00:00
- 2020-03-11 00:58:34.768755+00:00
- 2020-03-11 00:58:21.952063+00:00
It doesn't explain much, but if you can figure out the code, you'll have an idea of how it works. Here's the official Quickstart tutorial and a follow-on deeper dive tutorial that goes over everything in much more detail than my little code snippet.
FWIW, I tried coming up with the same thing but using the REST API and ran into some perms problem (403). Maybe I'll revisit again later. (It was too difficult for me to accomplish just trying for 15-20 minutes.)
As far as projects go, a Google Cloud (Platform) project is a singular, logical entity for an application and its resources. At this time, every project can have one App Engine app and one NoSQL database (Cloud Datastore [now called Cloud Firestore in Datastore mode] or Cloud Firestore [referred to as Cloud Firestore in Native mode]... you pick). This means they can both be in the same project so you wouldn't have to worry about cross-project permissions.