小编Max*_*Max的帖子

exports.saveUser = functions.auth.user().onCreate(event => {
    
   const userId = event.data.uid
  
   const saveUserToListPromise = db.collection("users").doc(userId).set({
      "userId" : userId
   })
   
   var userCounterRef = db.collection("users").doc("userCounter");
   
   const transactionPromise = db.runTransaction(t => {
      return t.get(userCounterRef)
          .then(doc => {
              // Add one user to the userCounter
              var newUserCounter = doc.data().userCounter + 1;
              t.update(userCounterRef, { userCounter: newUserCounter });
          });
  })
  .then(result => {
      console.log('Transaction success!');
  })
  .catch(err => {
      console.log('Transaction failure:', err);
  });
  
  return Promise.all([saveUserToListPromise, transactionPromise])

})