CODEWITHSUNDEEP
javascriptdatabasefirebasetransactionsgoogle-cloud-firestore
labo28
labo28

Reputation: 91

Avoid two request at same time in firestore

I created a function to communicate with the firestore database. First, check if there is something in the relation. If not then add something. If something already exists then use the data and then delete the entry in the queried relation. But you have to add that in the function(else section). And now the question arises what happens when two users simultaneously perform the function. Is there a way to put the second user in a queue while the first user is done with the request?

let ref = db.collection('relation1').doc('test').collection('user');
      var checkForAdd = ref.get().then(snapshot => {
        if(snapshot.size < 1){
            db.collection('relation1').doc('test').collection('user').add({
                user: 'Test',
                createdAt: Date.now()
            }).catch(err =>{
                console.log(err)
            })
        }

Upvotes: 0

Views: 2152

Answers (1)

Callam
Callam

Reputation: 11539

Cloud Firestore supports atomic operations for reading and writing data. In a set of atomic operations, either all of the operations succeed, or none of them are applied.

https://firebase.google.com/docs/firestore/manage-data/transactions

// Create a reference to the user doc you want to create if it doesn't exist.
const userCollectionRef = db.collection('relation1').doc('test').collection('user');
const userDocRef = userCollectionRef.doc('documentID');

return db.runTransaction(transaction => {
    // This code may get re-run multiple times if there are conflicts.
    return transaction.get(userDocRef).then(userDoc => {
        if (userDoc.exists) {
            // If something already exists then use the data and
            // then delete the entry in the queried relation.
        } else {
            transaction.update(userDocRef, {
                user: 'Test',
                createdAt: Date.now()
            });
        }
    });
}).then(() => {
    console.log("Transaction successfully committed!");
}).catch(error => {
    console.log("Transaction failed: ", error);
});

Upvotes: 3

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