CODEWITHSUNDEEP
javascripthtmlcollectionspromisegoogle-cloud-firestore
Filip Degenhart
Filip Degenhart

Reputation: 538

Handling firestore tasks with Promises

I am new to Promises for Firestore. I have to run this task: 

db.collection("users").doc(user_uid).collection("grades").doc("g").collection("es111").get().then(function(querySnapshot) {
            querySnapshot.forEach(function(doc) {
              db.collection("users").doc(user_uid).collection("grades").doc("g").collection("es111").doc(doc.id).delete();
            });
          })
          .catch(function(error) {
            console.log("Error getting documents: ", error);
          });

Here is the first Problem. This task should notice me when its finished. So only if al documents in the collection are deleted. I try to handle this with a promise. I am not sure maybe there are other ways. Thanks in advance.

~filip

Upvotes: 0

Views: 50

Answers (1)

Alexander Staroselsky
Alexander Staroselsky

Reputation: 38777

You may be able to use Promise.all to return a Promise when all delete() actions have completed that you can use with then()/catch() to perform an action or handle errors. As delete returns Promise<void> we can push each delete action to an array of promises that we can use with Promise.all():

function foo(user_uid) {
  return db.collection("users").doc(user_uid).collection("grades").doc("g").collection("es111").get().then(function(querySnapshot) {
    let promises = [];

    querySnapshot.forEach(function(doc) {
      // add each delete() promise to promises array
      promises.push(db.collection("users").doc(user_uid).collection("grades").doc("g").collection("es111").doc(doc.id).delete());
      // or more simply
      // promises.push(doc.ref.delete());
    });

    return Promise.all(promises);
  })
  .catch(function(error) {
    console.log("Error getting documents: ", error);
  });
}

// ...

// usage
foo()
  .then(() => console.log('Success!'))
  .catch(err => console.error(err));

Another option to consider is using batched writes:

db.collection("users").doc(user_uid).collection("grades").doc("g").collection("es111").get().then(function(querySnapshot) {
    const batch = db.batch();

    querySnapshot.forEach(function(doc) {
      batch.delete(doc.ref);
    });

    return batch.commit();
  })
  .then(() => console.log('Batched delete completed!'));

It looks like batched writes support a maximum of 500 operations at at time. Notice that you can simply the delete by using DocumentSnapshot.ref to reference the individual document instead of re-writing the query.

Hopefully that helps!

Upvotes: 2

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