Monday, February 28, 2011

Design Patterns Explained

Design patterns are high-level abstract solution templates. Think of them as blueprints for solutions rather than the solutions themselves. You won’t find a framework that you can simply apply to your application; instead, you will typically arrive at design patterns through refactoring your code and generalizing your problem. Design patterns aren’t just applicable to software development; design patterns can be found in all areas of life from engineering to architecture. In fact, it was the architect Christopher Alexander who introduced the idea of patterns in 1970 to build a common vocabulary for design discussion. He wrote:
The elements of this language are entities called patterns. Each pattern describes a problem that occurs over and over again in our environment and then describes the core of the solution to that problem in such a way that you can use this solution a million times over without ever doing it the same way twice.

The origins of the design patterns that are prevalent in software architecture today were born from the experiences and knowledge of programmers over many years of using object-oriented programming languages.

Patterns are essential to software design and development. They enable the expression of intent through a shared vocabulary when problem solving at the design stage as well as within the source code. Patterns promote the use of good object-oriented software design, as they are built around solid object-oriented design principles. Patterns are an effective way to describe solutions to complex problems. With solid knowledge of design patterns, you can communicate quickly and easily with other members of a team without having to be concerned with the low-level implementation details. Patterns are language agnostic; therefore, they are transferable over other object-oriented languages. The knowledge you gain through learning patterns will serve you in any first-class object-oriented language you decide to program in.

The useful and ultimate value of design patterns lies in the fact that they are tried and tested solutions, which gives confidence in their effectiveness. Design patterns are all about the reuse of solutions. All problems are not equal, of course, but if you can break down a problem and find the similarities with problems that have been solved before, you can then apply those solutions. After decades of object-oriented programming, most of the problems you’ll encounter will have been solved countless times before, and there will be a pattern available to assist in your solution implementation. Even if you believe your problem to be unique, by breaking it down to its root elements, you should be able to generalize it enough to find an appropriate solution. The name of the design pattern is useful because it reflects its behavior and purpose and provides a common vocabulary in solution brainstorming. It is far easier to talk in terms of a pattern name than in detail about how an implementation of it would work.
Reference : Professional ASP.NET Design Patterns by Scott Millett

Tuesday, February 8, 2011


CONTEXT_INFO() function returns the contenxt_info value that was set for the current session or batch by using the SET CONTEXT_INFO statement. It can associate up to 128 bytes of binary information with the current session or connection.

You can set the context_info using:
SET CONTEXT_INFO { binary_str | @binary_var }
where binary_str is a binary constant / @binary_var is varbinary or binary variable.

In SQL server, session context information is also stored in the context_info columns of the following system views:
  • sys.dm_exec_requests
  • sys.dm_exec_sessions
  • sys.sysprocesses

The preferred way to retrieve the context information for the current session is to use the CONTEXT_INFO() function.

SET CONTEXT_INFO 0x1111122222

  • Passing information from a stored procedure that performs DML operations to the triggers Read more
  • To make SQL table will never be modified except via a stored procedure Read more