I connect the database from React Native project.
In my Firestore database Buildings/Taipei, i want to get all of the collection ids like 201 202 203

I try to use the code:
const db = firebaseApp.firestore();
db.collection('Buildings').doc('Taipei')
.get()
.then(doc => {
console.log('get doc is =>');
console.log(doc);
}).catch(error => {
console.log(`error is ${error}`);
});
I can't see any collection id in the doc.

Any help would be appreciated. Thanks in advance.