I periodically ponder how to best design an application whose every business rule exists in just a single location. (While I know there is no proverbial “best way” and that designs are situational, people must have a leaning toward one practice or another.) I work for a shop where they prefer to house as much of the business rules as possible in the database. This requires developers in many cases to perform identical front-end validations to avoid sending data to the database that will result in an exception—not very DRY. It grates me anytime I find myself duplicating any kind of logic—even lowly validation logic. I am a single-point-of-truth purist to an anal degree.

On the other end of the spectrum, I know of shops that create dumb databases (the Rails community leans in this direction) and handle all of the business logic in a separate tier (in Rails the models would house “most” of this). Note the word “most” which implies that some business logic does end up spilling into other places (in Rails it might spill over into the controllers). In way, a clean separation of concerns where all business logic exists in a single core location is a Utopian fantasy that’s hard to uphold (n-tiered architecture or not).

Furthermore, is see the “Database as a fortress” and would agree that it should be built on constraints that cause it to reject bad data. As such, I hold principles that cause a degree of angst as I attempt to balance them.

How do you balance the database-as-a-fortress view with the desire to have a single-point-of-truth?