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How to design and build a DBC system using C#, and NVelocity.
Previous Posts


Design by Contract
Sunday, June 12, 2005

May was a quiet month

It's been almost a month since the last time I posted, and I have made a few changes to the DBC framework since then. I'm making changes now in readiness for release to GotDotNet or Sourceforge. So I'm just making sure everything is as logical and consistent as I can make it. Firstly, I have completely rewritten the NVelocity template assembly to simplify it even more (as if that were possible!). Now you can use it like this:
public void TestDefaultCreationOfTemplate()
  ITemplate tpl = TemplateManager.CreateTemplate(@"Hello" +
    " ${otherpart}");
  tpl["otherpart"] = "world";
  Assert.AreEqual(tpl.ProcessedOutput, "Hello world",
    "strings didn't match");
The observant amongst you will also notice that I'm now using unit test cases from visual studio 2005's unit testing framework - why MS couldn't just use NUnit I don't know (well I do, and it doesn't reflect well on them), especially since their framework seems excessively complicated when using autogenerated tests. Anyway, the template class is now just a very thin veneer over the velocity framework. I am still able, should the need arise, to swap out NVelocity and replace it with something else, but the changeover was mostly involved in recompilation of NVelocity to .NET 2.0 and to add a strong name for deployment to the GAC. I've placed the code generation templates into the Core assembly as resources to allow easier deployment and to make them tamper proof and to get rid of the needless configuration settings to allow the system to find the templates. I've broken out the predicate attributes and the exception types to a separate assembly, so development can be done with DBC attrs even if the DBC system is not in use. It also means the attributes can be put to other uses like documentation or validation. Right now, I'm mostly in performance tweeking and refactoring mode. Here's an example of one of the tests I'm using that shows how the system is to be used now:
public void TestTimeToCreateAThousandProxyObjectPairs()
  ArrayList al = new ArrayList();
  DbcProxyDynRTCF cf = new DbcProxyDynRTCF();
  int totalToCreate = 10000;
  DateTime start = DateTime.Now;
  for (int i = 0; i < totalToCreate; i++)
  TimeSpan durn = DateTime.Now - start;
  double d = durn.TotalMilliseconds / ((double)totalToCreate);
  Debug.WriteLine("Average time to create a proxy-object pair" +
    " (ms): " + d.ToString());
  Assert.IsTrue(durn.TotalMilliseconds < ((double)
    totalToCreate) * .17);
Currently the average time needed to instantiate a proxy with a target object is around .2 milliseconds. Interestingly it was around 0.16ms with .NET 1.1, but now I'm working with .NET 2.0 the performance is roughly 25% slower. It may be that some of the techniques I am using can be performed in a better way now, but that remains to be seen -- the only deprecated feature that I have not updated is in my use of CreateCompiler to compile the generated code. This piece of code gets called only once, before the timer is turned on. So it couldn't affect the code performance unduly. So where is this much publicised performance boost that we are supposed to get from .NET 2.0?
public CompilerResults GenerateAssembly()
  Assert(SourceCollection != null && SourceCollection.
     Count > 0);
  CSharpCodeProvider cscp = new CSharpCodeProvider();
  ICodeCompiler compiler = cscp.CreateCompiler();
  CompilerParameters cp = ConstructCompilerParameters();
  string[] classes = new string[SourceCollection.Count];
  SourceCollection.CopyTo(classes, 0);
  CompilerResults cr = compiler.CompileAssemblyFromSourceBatch
    (cp, classes);

  if (cr.Errors.HasErrors)
    foreach (CompilerError ce in cr.Errors)
  return cr;

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