How do I provide visibility to records for users based on field criteria? My demand is: When I have some specific object Files with some specific products the users that contact in this accounts that have this product will see this register of Files. Like:
How to reach this solution? I think about a trigger on the object File that will check the accounts that contain the same product, and then, create a sharing rule for that, but I don`t know if is the best option and also, because of the limit of 300. It's that any other way?
Uh, interesting one! You mean real Files (ContentDocument, ContentVersion), not some custom object, right? Files are bit tricky, normally community user would see all files attached to their account + special "Asset" files.
trigger on the object File (...) and then create a sharing rule
Don't think it'll work. Sharing rules are metadata, not data. You'd need a deployment or cheat by making API callout. But also sharing rules don't really work for community, you're supposed to use sharing sets.
You could try making ContentDocumentLinks between the file header (ContentDocument) and Account. And yes, you should be able to do it from trigger. I don't remember if there are limitations like 1 file can be linked at most to X records, this might be tricky. a change of Account's product would potentially mean lots of links to add/remove, maybe move this bit to @future / Queueable.
Alternatively you could just make all files & their folders visible in the community, maybe even for guest user (look into Asset files?). And just show / hide links to their folders based on what's on the account. Bit "security by obscurity" but well, fairly easy to do, adding/removing products wouldn't mean lots of operations. Depends if these files are somewhat sensitive or it's more about guiding the user to what they're interested in.
Ask on https://salesforce.stackexchange.com/ too, somebody can have even better ideas.