If factory function returns null, does GetOrSet save null in cache?

[pbolduc]

I have a situation where my factory method will return null of a record is not found. Will the GetOrSet / GetOrSetAsync store null in the cache, or does it just return null and nothing is cache? I do not want null to be cached. It wasn't clear from the docs (or I missed it).

[jodydonetti]

Hi @pbolduc and thanks for using FusionCache!

FusionCache caches null like any other value, because normally not caching null will lead to problems.

For example let's say that someone asks your service for /product/123 and that product doesn't exist: the factory goes to the database, returns null, but null is not cached. This means that evey single request for it will go to the database, again and again.

Basically that is a DoS/DDoS waiting to happen.

As an example, this is what StackOverflow does:

It also allows the caching of a null value and makes that handling not special-cased. In other words, you can tell the difference between “It’s not cached” and “We looked it up. It was null. We cached that null. STOP ASKING!”

Having said that, if you think this is the good thing to do in your scenario and you really need to not cache nulls (or, I would suggest, at least to cache them for a lower Duration), you can use Adaptive Caching to achieve that.

Hope this helps.

[jodydonetti]

It wasn't clear from the docs (or I missed it)

It's in the main readme, in the "Something more" details:

Good catch though: probably I should put it also somewhere else to be more prominent.

[pbolduc]

You are awesome!

[jodydonetti]

Thanks @pbolduc 😊 !

If you'd like, let me know which path you took (cache for less or don't cache).

Also, can you please mark one of my comment as the answer?

Thanks!

[pbolduc]

I used the adaptive caching approach. In my case, I realized after the service I was calling would return empty collection if the data was not found. I cache it for 5 minutes, otherwise I cache for 1 day - https://github.com/bcgov/jag-traffic-courts-online/blob/d7f6ed4a6b4a09301d82a6383fdfeaa963b7fecc/src/backend/TrafficCourts/Citizen.Service/Services/Tickets/Search/TicketSearchService.cs#L198-L226

[jodydonetti]

Got it, thanks for sharing!