Google Firestore - How To Get Several Documents By Multiple Ids In One Round-trip?

I am wondering if it's possible to get multiple documents by a list of ids in one round trip (network call) to the Firestore database.

Solution 1:

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"])

Solution 2:

They have just announced this functionality, https://firebase.googleblog.com/2019/11/cloud-firestore-now-supports-in-queries.html .

Now you can use queries like, but mind that the input size can't be greater than 10.

userCollection.where('uid', 'in', ["1231","222","2131"])

Solution 3:

In practise you would use firestore.getAll like this

asyncgetUsers({userIds}) {
    const refs = userIds.map(id =>this.firestore.doc(`users/${id}`))
    const users = awaitthis.firestore.getAll(...refs)
    console.log(users.map(doc => doc.data()))
}

or with promise syntax

getUsers({userIds}) {
    const refs = userIds.map(id =>this.firestore.doc(`users/${id}`))
    this.firestore.getAll(...refs).then(users =>console.log(users.map(doc => doc.data())))
}

Solution 4:

You could use a function like this:

functiongetById (path, ids) {
  return firestore.getAll(
    [].concat(ids).map(id => firestore.doc(`${path}/${id}`))
  )
}

It can be called with a single ID:

getById('collection', 'some_id')

or an array of IDs:

getById('collection', ['some_id', 'some_other_id'])

Solution 5:

No, right now there is no way to batch multiple read requests using the Cloud Firestore SDK and therefore no way to guarantee that you can read all of the data at once.

However as Frank van Puffelen has said in the comments above this does not mean that fetching 3 documents will be 3x as slow as fetching one document. It is best to perform your own measurements before reaching a conclusion here.