Hansen8 Developers Group Meeting IV

Microsoft Enterprise Library

Raja introduced us to Microsoft Enterprise Library via five examples:

1. Dependency Injection
   
2. Exception Handling
   
3. Logging
   
4. Caching
   
5. Validation
   

To me, the best part was that the app.config file can be edited visually making it a straightforward matter to modify logging, exception handling and validation rules. Russell pointed out that this is an example of Aspect Oriented Programming which allows for the separation of cross-cutting concerns.

Dependency Injection was demonstrated via a UnityContainer which acts as a sort of factory to produce an instance of RateTable containing a strategy:

        using (IUnityContainer container = new UnityContainer())
        {
            container.LoadConfiguration();
            var rt = container.Resolve(); 
            rt.Calculate();
        }

The specific strategy is specified in the app.config:

  <unity xmlns="http://schemas.microsoft.com/practices/2010/unity">
    <container>
      <register type="IRateAlgorithm" mapTo="FlatRate"/>
    </container>
  </unity>

Exception Handling requires an ExceptionManager instance:

    exManager = EnterpriseLibraryContainer.Current.GetInstance();
    catch ( Exception e) exManager.HandleException(e, "BillRun"); 

Without the Enterprise Library Configuration Editor installed on my machine it's difficult to describe the app.config, but essentially it maps "BillRun" exceptions (a policy) through a exception type to an exception handler allowing logging, substitution and custom handling of the exception.

Logging is very similar to exceptions. A LogWriter instance is required. Also, a LogEntry object further clarifies the message category:

	private LogWriter writer = EnterpriseLibraryContainer.Current.GetInstance();
	public void DoLogging()
	{
	    LogEntry log = new LogEntry();
	    log.Message = "Delinquency Run Starting....";
	    log.Categories.Add(Category.General);
	    log.Categories.Add(Category.BillRun);
	    log.Priority = Priority.Normal;
	    writer.Write(log);
	}

Caching contains too much code...skipping

Validation requires a ValidatorFactory to create a specific validator:

  valFactory = EnterpriseLibraryContainer.Current.GetInstance();
  customerValidator = valFactory.CreateValidator();

Validation and ValidationResult:

	ValidationResults results = customerValidator.Validate(customer);
	if (!results.IsValid)
	{
		StringBuilder builder = new StringBuilder();
		builder.AppendLine("Customer is not valid:");
		foreach (ValidationResult result in results)
		{
			//do stuff
		}
	}

At a minimum using Microsoft.Practices.EnterpriseLibrary give guidance for basic coding practices.