Funkwhale has some handy docs on its implementation of ActivityPub.
https://docs.funkwhale.audio/federation/index.html
Gives a few basic hints as to how you might go about actually implementing ActivityPub in an app with a DB.
https://docs.funkwhale.audio/federation/index.html
Gives a few basic hints as to how you might go about actually implementing ActivityPub in an app with a DB.