How to Pipeline Several Request to Firebase in Order to Fetch Data from Multiple Nodes at The Same Time

How to pipeline several request to Firebase in order to fetch data from multiple nodes at the same time

Probably the best way to do this in Swift would be to use DispatchGroups -

var nodes: [String] = ["node1", "node2", "node3", "node4"]

let dispatchGroup = DispatchGroup()

for node in nodes {

    dispatchGroup.enter()

    Database.database().reference().child(node).child(uid).observeSingleEvent(of: .value, with: { (snapshot) in
      //Do something  
      dispatchGroup.leave()
    }

}

dispatchGroup.notify(queue: .main, execute: {
    //Called when all requests have been fulfilled 
}) 

Google Firestore - How to get several documents by multiple ids in one round-trip?

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 Now Supports IN Queries!

myCollection.where(firestore.FieldPath.documentId(), 'in', ["123","456","789"])

Firebase performance - fetching nodes

Doing a "client-side join" in Firebase is not nearly as expensive as you might expect. See this answer: Speed up fetching posts for my social network app by using query instead of observing a single event repeatedly

If you directly access the node (only calling new Firebase() and child()), no query is needed, so you won't need an index. If you're calling orderByChild() or orderByValue() you should add an index.

Firebase real time database, get values from different locations in one snapshot

You can only load:

• a single complete node
• a subset of all child nodes matching a certain condition under a single node

It seems that what you are trying to do is get a subset of the child nodes from multiple roots, which isn't possible. It actually looks like you're trying to do a join, which on Firebase is something you have to do with client-side code.

Note that loading the subsequent nodes is often a lot more efficient than developers expect, since Firebase can usually pipeline the requests (everything goes over a single web socket connection). For more on this, see http://stackoverflow.com/questions/35931526/speed-up-fetching-posts-for-my-social-network-app-by-using-query-instead-of-obse/35932786#35932786.

Get data from multiple references from Firebase realtime database in one query javascript

To load multiple nodes based on their key, you'll need a separate call for each node/key. It's essentially a client-side join of the data from the two nodes:

const usersMessages = firebase.database().ref(`users/${userUid}/messages`);
usersMessages.on('value', async (snapshot) => {
    let usersMessages = [];
    snapshot.forEach((child) => }
        let messageId = child.key;
        let messageSnapshot = await firebase.database().ref(`messages/${messageId}`).get()
        const message = messageSnapshot.val();
        usersMessages.push(message);   
    });
});

Firebase : How to removeObserver(withHandle:) after observeSingleEvent()?

Since databaseReference.observeSingleEvent(...) doesn't return a handle that you can remove the only option is to use databaseReference.observe(...).

Just remove the handle manually once you need to OR when the first event fires.

Update

Try using this extension:

public extension FIRDatabaseReference {

    @discardableResult
    public func observeOneEvent(of eventType: FIRDataEventType, with block: @escaping (FIRDataSnapshot) -> Swift.Void) -> FIRDatabaseHandle {

        var handle: FIRDatabaseHandle!
        handle = observe(eventType) { (snapshot: FIRDataSnapshot) in
            self.removeObserver(withHandle: handle)
            block(snapshot)
        }

        return handle

    }

}

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