Best way to organize firebase writes on update trigger - node.js

Question

There may be more than one correct answer to this question, but here's my issue: I have a user document in firebase with many fields that can be updated and which interact in different ways. If one field is updated, it may require a change to another field on the backend. Is it better to have a whole bunch of if statements each with their own write action if the condition is met or, or do single write at the end of the function for all the fields that might change. If a field does not change, I would have to write its original value back to itself. That seems clunky, but so does the other option. Am I missing a third option? What is the best practice here?
Here's an example of what I'm talking about. Updating fields one at a time is what I have now, which looks like this:
export const userUpdate = functions.firestore
.document("users/{userID}")
.onUpdate(async (change) => {
const beforeData = change.before.data();
const afterData = change.after.data();
// user levels up and gets more HP
if(beforeData.userLevel != afterData.userLevel){
const newMaxHP = 15 + 5 * afterData.userLevel;
change.after.ref.update({
maxHp: newMaxHP
})
}
//update user rating
if (beforeData.numberOfRatings != afterData.numberOfRatings) {
const newRating = placerRating(beforeData.userRating, beforeData.numberOfRatings, afterData.latestRating);
change.after.ref.update({
userRating: newRating
})
}
//replenish user funds from zero
if (afterData.money == 0){
change.after.ref.update({
money: 20
})
}
If I did it all in a single write, the if statements would assign a value to a variable, but not update the firestore document. Each if statement would include an else statement assigning the variable to the field's original value. There would be a single write at the end like this:
change.after.ref.update({
maxHp: newMaxHP,
userRating: newRating,
money: 20
})
I hope that helps.
[edit to add follow-up question about updating a map value]
#Dharmaraj's answer works great, but I'm struggling to apply it when updating a map value. BTW - I'm using Typescript.
Before using #Dharmaraj's solution, I was doing this:
admin.firestore().collection("users").doc(lastPlayerAttacker).update({
"equipped.weapon.usesLeft": admin.firestore.FieldValue.increment(-1)
});
Using the update object, I'm trying it like this, but I get the error "Object is of type 'unknown'"
const lastPlayerUpdates:{[key:string]:unknown} = {};
lastPlayerUpdates.equipped.weapon.usesLeft = admin.firestore.FieldValue.increment(-1);
admin.firestore().collection("users").doc(lastPlayerAttacker).update(lastPlayerUpdates);
Any advice on how to fix it?

Answer 1

Every time you call update(), you are being charged for 1 write operation. It'll be best to accumulate all updated fields in an object and then update the document only once as it'll be more efficient too. Try refactoring the code as shown below:
export const userUpdate = functions.firestore
.document("users/{userID}")
.onUpdate(async (change) => {
const beforeData = change.before.data();
const afterData = change.after.data();
const updatedData = {};
// user levels up and gets more HP
if (beforeData.userLevel != afterData.userLevel) {
const newMaxHP = 15 + 5 * afterData.userLevel;
updatedData.maxHp = newMaxHP;
}
//update user rating
if (beforeData.numberOfRatings != afterData.numberOfRatings) {
const newRating = placerRating(beforeData.userRating, beforeData.numberOfRatings, afterData.latestRating);
updatedData.userRating = newRating;
}
//replenish user funds from zero
if (afterData.money == 0) {
updatedData.money = 20;
}
await change.after.ref.update(updatedData);
console.log("Data updated");
return null;
})