Where to put Business Rules on ASP.NET Web App, Repository Pattern
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I have been a little confused with trying to determine where to put the business rules for my application.

I am developing an web application using asp.net conventional web forms (not mvc) and on top of that I have a class library where I have the repository pattern for writing to database. I have a "Business Layer" in the repository pattern and also, I am writing stored procedures to affect the tables.

Where should I put for example, Mandatory field validation rules ? 

Other example would be, converting foreign currency to USD (i have an exchange rate table, currently I do it in sprocs).

Would you recommend staying away from the sprocs for rules and build everything in my repository business layer ? or In what cases do you recommend building rules and validations within the sprocs ?
