Firebase: Transaction with async/await

If you look at the docs you see that the function passed to runTransaction is a function returning a promise (the result of transaction.get().then()). Since an async function is just a function returning a promise you might as well write db.runTransaction(async transaction => {})

You only need to return something from this function if you want to pass data out of the transaction. For example if you only perform updates you won't return anything. Also note that the update function returns the transaction itself so you can chain them:

try {
    await db.runTransaction(async transaction => {
      transaction
        .update(
          db.collection("col1").doc(id1),
          dataFor1
        )
        .update(
          db.collection("col2").doc(id2),
          dataFor2
        );
    });
  } catch (err) {
    throw new Error(`Failed transaction: ${err.message}`);
  }

The above did not work for me and resulted in this error: "[Error: Every document read in a transaction must also be written.]".

The below code makes use of async/await and works fine.

try{
   await db.runTransaction(async transaction => {
       const doc = await transaction.get(ref);
       if(!doc.exists){
            throw "Document does not exist";
       }
       const newCount = doc.data().count + 1;
       transaction.update(ref, {
           count: newCount,
       });
  })
} catch(e){
   console.log('transaction failed', e);
}

IMPORTANT: As noted by a couple of the users, this solution doesn't use the transaction properly. It just gets the doc using a transaction, but the update runs outside of it.

Check alsky's answer. https://stackoverflow.com/a/52452831/683157

---

Take a look to the documentation, runTransaction must receive the updateFunction function as parameter. (https://firebase.google.com/docs/reference/js/firebase.firestore.Firestore#runTransaction)

Try this

var docRef = admin.firestore().collection("docs").doc(docId);
let doc = await admin.firestore().runTransaction(t => t.get(docRef));

if (!doc.exists) {throw ("doc not found");}
var newLikes = doc.data().likes + 1;

await doc.ref.update({ likes: newLikes });