A few links pertaining to my code contracts talk

I am giving an intro talk on Code Contracts tomorrow for the Central PA .NET Code Camp 2010.
Here a few links from that talk.

• Code Contracts web site
  


• Sample chapter on Code Contracts from Jon Skeet's book C# in Depth (second edition)
  


• Pex for Fun web site that I took examples from.
  


• Excellent series of blog posts from Kevin Hazzard on code contracts
  

Souce Code and other materials from Grokking ORMs talk

Here are the slides and source code from my talk at Central PA.NET Code Camp 2010 called Grokking Object-Relational Mappers. The zip file is at https://public.me.com/jwigger and is called Grokking_ORMs_9_10_2010.zip
Here is a few links covered in the talk.

• Julie Lerman's book, THE book on EF - Programming Entity Framework


• Frans Bouma, developer of LLBLGen has a lot of interesting, highly opinionated posts on his blog. This post explains his position on why LLBLGen works well with Entity Framework. I will post more on this topic but I do really like the LLBLGen designer and code generator used in combination with EF. Caveat Lector: I received a free developer license of LLBLGen to work on this presentation.


• NHibernate's Home is here at nhforge.org


• Upcoming NHibernate 3 Cookbook by Jason Dentler and his Hanselminutes podcast episode


• Jeremy Miller's MSDN article on persistence ignorance and the unit of work pattern.


• 
  An explanation of the Select N+1 problem that relates to lazy loading objects.

Code Contracts Support within .NET Framework BCL

Code Contracts were one of the Holy Grails in Computer Science when I received my bachelor’s degree in 1997. Yes, there was research aplenty including my professor Dr. Tim Wahls’ work with the Larch and later Java Modeling Language (JML) approaches to Design By Contracts. However, it was far removed from mainstream programming. Microsoft is poised to change that with Code Contracts.

Code Contracts allow formal specifications to be applied to code. These consist of preconditions, post-conditions, and object invariants. The idea is that code can have its intent made clearer for callers by specifying characteristics of valid use and code that calls code with contracts available can be more reliable by guaranteeing that the contracts aren’t broken. Compile-time checking allows abuse of contracts to be caught very early in the development cycle. An excellent chapter by Jon Skeet from C# in Depth (second edition) covering contracts is available here.

Code Contracts are still a development labs product but Microsoft has already modified some BCL code to support contracts. An earlier draft of Skeet’s chapter illustrates the progress is making. An example showing a case beyond what Code Contracts were NOT aware of is now caught by .NET 4 and the static contract checker! The system random number generator Next function takes two arguments , a lower bound and upper bound, and produces a pseudorandom number >= lower bound and < upper bound. Looking at the BCL source available through Microsoft’s symbol server shows a contract that stipulates that the lower bound can’t be larger than the upper bound.

 int randomNum;  
 Random randomGenerator = new Random();  
 randomNum = randomGenerator.Next(7, 1);  
 //caught as an exception violation   

If we have a function with a precondition that an input number is a valid output of a six-sided die, then the static contract checker uses the contracts built-in to the BCL to support its inference. The static check has found that the output of the Next function will always produce legal input.

 Random randomGenerator = new Random();  
 randomNum = randomGenerator.Next(1, 7);