What is the right way to update createdAt and updatedAt date fields for a document in firestore?

Question

I have a document collection called schools for which we have kept fields called createdAt and updatedAt. I'm updating these fields using firestore cloud trigger functions in onCreate and onUpdate triggeres respectively.

The problem I'm facing here is, these field updates will call onUpdate trigger again unnecessarily. For these to handle, I've written an additional function called skipOnUpdateTrigger

const excludeFields = ["createdAt", "UpdatedAt"]

shouldSkipOnUpdateTrigger = function(docDataOld, docDataNew, excludeFields){
    for(let i of excludeFields){
        if (docDataOld[i] !== docDataNew[i])
            return true;
 }
    return false;
}

Is there a better way I can handle this situation to avoid those extra triggers?

Frank van Puffelen Frank van Puffelen · Accepted Answer · 2019-07-08T14:21:34

The simplest way I've found is to prevent the need for Cloud Functions altogether, and let the client include the lastUpdated value in each write with a server-side timestamp.

You can enforce this in security rules, by checking:

allow update: if request.resource.data.lastUpdated = request.time

What is the right way to update createdAt and updatedAt date fields for a document in firestore?

2 Answers