Patterns, gotchas and small wins from fifteen-odd years of .NET and web work — the Regira packages and modules, entity pipelines, editorial front-ends and everything between.
Business rules that refuse a change live in one place, hold for every screen and import, and cover deleting as well as saving. A user who breaks three rules hears about all three at once, next to the fields they concern.
A rule can be checked when a request arrives, just before a record is stored, or by the database itself. In the wrong place it is skipped by imports and deletes, judged on a value the application has not tidied yet, or answered with a message nobody can act on. Where each kind of rule belongs, and why.