Defining Your Own Logging Transactions

You can use the codeless configuration system even if your application is not based on ASP.NET. For instance, you can define transactions in a service processing requests from a queue, or files from an input directory.

This article explains how to do it.

To define custom transactions and use them in the policy XML file:

1. Choose a name for your transaction type, for instance MorningBatch.

2. Create the expression model class, for instance MorningBatchExpressionModel . That will become the type of the Request property that is visible to the XML policy file.

   public readonly struct MorningBatchExpressionModel
   {
       internal MorningBatchExpressionModel( string fileName )
       {
           this.FileName = fileName;
       }
   
       public string FileName { get; }
   
       public DateTime LastWriteTime => File.GetLastWriteTime(this.FileName);
   
       public int Size => new FileInfo(this.FileName).Length;
   
   }
   

3. Derive a class from LogEventMetadata and use your expression model type as the generic parameter instance. Expose a singleton instance of this class.

   internal sealed class MorningBatchMetadata : LogEventMetadata<MorningBatchExpressionModel>
   {
       public static readonly MorningBatchMetadata Instance = new MorningBatchMetadata();
   
       private MorningBatchMetadata() : base( "MorningBatch" )
       {
       }
   
       public override MorningBatchExpressionModel GetExpressionModel( object data )
         => new MorningBatchExpressionModel( (string) data );
   
   }
   

4. In your source code, find the place where the transaction starts and ends. Create an OpenActivityOptions instance and pass a LogEventData created from your singleton LogEventMetadata.

5. Call the ApplyTransactionRequirements(ref OpenActivityOptions) method. This will apply the logging policies to the OpenActivityOptions. You can skip this method call and force a transaction to be opened by directly setting the TransactionRequirement property.

6. Call the OpenActivity<T>(in T, in OpenActivityOptions) method at the beginning of your transaction.

7. Call SetSuccess(in CloseActivityOptions) or SetException(Exception, in CloseActivityOptions) at the end.

   Your transaction code will now look like this:

   var logSource = LogSource.Get();
   
     foreach ( var fileName in Directory.GetFiles( ".", "*.batch") )
     {
   	var options = new OpenActivityOptions(
   							LogEventData.Create( filename, MorningBatchMetadata.Instance ),
   							LogActivityKind.Transaction );
   
   	logSource.ApplyTransactionRequirements( ref options  );
   
   	var transaction = logSource.Default.OpenActivity(
   							Formatted( "Processing {FileName}", fileName ),
   							options )
   
   	try
   	{
   
   		// The original transaction processing code is here.
   
   		transaction.SetSuccess();
   	}
   	catch ( Exception e )
   	{
   		transaction.SetException( e );
   		throw;
   	}
   }
   

8. You can now create a configuration file that references your expression model. For instance, the following file will enable logging for batch files larger than a thousand bytes:

   <logging>
       <verbosity level='warning'/>
       <transactions>
           <policy type='MorningBatch' if='t.Request.Size > 1000' name='Policy1'>
               <verbosity>
                   <source level='debug'/>
               </verbosity>
           </policy>
       </transactions>
   </logging>