Monday, July 13

Another Standards Discussion: Views and Business Rules

Let’s say that the business you work for has also been around for many years, and in that time loads of little rules about the data have appeared. Market A works differently to market B. This car shouldn’t be included in this list of products. When pulling together a list of shoppers, we only care about those that have credit cards.

Every time a new project comes up, a new part of a public facing website or a new module in an in-house application, new stored procs are developed. Often, these procs are written by people who weren’t around when the DB schema involved was designed, or they haven’t got all of those little rules I discussed above memorized. Who does?

This is where Views can come in handy. Instead of building each of those annoying little rules into each new Stored Procedure that’s developed, build them into Views, and point all Stored Procs towards Views instead of Tables.

And I mean ALL Stored Procs. As a standard. If you follow this standard, you can be sure that when it’s time to implement a new business rule, you can find the appropriate View, alter some code, and all the dependant Stored Procedures will now follow that new business rule.

For example, you have a table called Lotto.Entry. It records who has entered a lottery, and how old they are. Supplying the website, there are three hundred stored procedures which access data from this table. The CEO at your company decides that it’s no longer ethical to be reporting on people under 17 who have entered the lottery. If all those 300 Stored Procedures are pointing towards the table, you’re faced with moving data around, or changing all of those procs. If the procs are instead pointing towards Lotto.vEntry, that view can have a “WHERE Entry.Age > 17” clause added. Other Views should point towards this View instead of the underlying Table, so that the business rules are “inherited” across the system.

Another advantage is that the business rules are centralized. You know to look towards the basic view of a table if you want to know how its data is handled.

Pretending to delete data is another thing that can be done in views. Let’s say you want the users of the website/UI to feel like they’re deleting data, but you want an audit trail on that data, and you simply want to hide it from the users. Add an “IsDeleted” field to your table, and a “WHERE IsDeleted = 0” clause to the base view of that table. The data is then easily “undeleted” in cases of errors.

Views are a centralized, transparent and predictable way of implementing rules in which your data is accessed.

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