I am wondering if it's possible to get multiple documents by list of ids in one round trip (network call) to the Firestore.
if you're within Node:
https://github.com/googleapis/nodejs-firestore/blob/master/dev/src/index.ts#L978
/**
* Retrieves multiple documents from Firestore.
*
* @param {...DocumentReference} documents - The document references
* to receive.
* @returns {Promise<Array.<DocumentSnapshot>>} A Promise that
* contains an array with the resulting document snapshots.
*
* @example
* let documentRef1 = firestore.doc('col/doc1');
* let documentRef2 = firestore.doc('col/doc2');
*
* firestore.getAll(documentRef1, documentRef2).then(docs => {
* console.log(`First document: ${JSON.stringify(docs[0])}`);
* console.log(`Second document: ${JSON.stringify(docs[1])}`);
* });
*/
This is specifically for the server SDK
UPDATE: "Cloud Firestore [client-side sdk] Now Supports IN Queries!"
https://firebase.googleblog.com/2019/11/cloud-firestore-now-supports-in-queries.html
myCollection.where(firestore.FieldPath.documentId(), 'in', ["123","456","789"])