More than one way to sort a List<>

One operation you occasionally need to perform is sorting a generic list of objects. Often developers code handle with an inline delegate. If I wanted to sort a collection of boardgames by rating, my code might look like this:

  games.Sort(

      delegate(BoardGame a, BoardGame b)

      {

          if (a.Rating < b.Rating)

              return 1;

          if (a.Rating > b.Rating)

              return -1;

          return 0;

      });

Although this works, it tends to look a bit cluttered. It also increases a method's complexity and doesn't adhere to the idea of separation of concerns. If we only need to sort Boardgames in this one location, a better solution is to move the comparison code into a separate method in the same class. The new method looks like this:

  public int CompareBoardgamesByRank(BoardGame a, BoardGame b)

  {

      if (a.Rating < b.Rating)

          return 1;

      if (a.Rating > b.Rating)

          return -1;

      return 0;

  }

Our call to Sort looks like this:

  games.Sort(CompareBoardgamesByRank);

This makes the code much cleaner for a single sort. If we want to sort Boardgames by rating from multiple locations, we need a better place to store the comparison method. If we implement IComparable on our Boardgame class, we can create a CompareTo method on the class like so:

  public int CompareTo(object obj)

  {

      BoardGame b = (BoardGame)obj;

      if (Rating < b.Rating)

          return 1;

      if (Rating > b.Rating)

          return -1;

      return 0;

  }

Since the class now has a default comparison, we no longer need to specify a delegate when calling Sort - the CompareTo method will automatically be executed with an empty call:

  games.Sort();

What if we need additional comparison methods for our Boardgame? An easy way to handle this is to create static methods on the class, which will be available anywhere that Boardgame can be accessed. Here are a couple methods I've added to my Boardgame class:

  public static int CompareByName(BoardGame a, BoardGame b)

  {

      return string.Compare(a.Name, b.Name);

  }

  public static int CompareByRankAssending(BoardGame a, BoardGame b)

  {

      if (a.Rating > b.Rating)

          return 1;

      if (a.Rating < b.Rating)

          return -1;

      return 0;

  }

Which I can now pass into the Sort method:

  games.Sort(BoardGame.CompareByRankAssending);

Refactoring assemblies without breaking existing apps

Over time, most development shops identify common code that needs to be used across multiple projects. This code is eventually collected into a single assembly, usually something like Common.dll or Utilities.dll. In the beginning this is a decent way to eliminate code duplication. Over time, however, this single assembly becomes difficult to maintain.

At this point the obvious fix is to split the assembly into multiple smaller ones. Unfortunately, by then the single assembly is used on numerous projects. A major refactoring now requires extensive changes across all of these referencing applications. This realization usually stops any refactoring effort, leaving the utilities assembly to continue growing larger and more unwieldy.

To look at potential solutions, I've created a Utilities assembly with the following Logger class:

  namespace Utilities

  {

      public class Logger

      {

          public void LogError(string message)

          {

              Debug.WriteLine("Error: " + message);

          }

      }

  }

The goal is to move this class to a separate assembly called LoggingUtilities.

One solution is to use the TypeForwardedTo attribute. This is an assembly-level attribute that flags a specified class as having moved. To use this, I start by moving the Logger class to my new assembly. Note that I keep the same namespace as before - this is required for the forwarding to work.

Next I add a reference to LoggingUtilities within Utilities.

Finally, I open up AssemblyInfo.cs file in the Utilities project and add the following line:

  [assembly: TypeForwardedTo(typeof(Utilities.Logger))]

If I recompile the dlls and drop them in a folder with my existing application, it will continue to function even though the class has been moved.

This takes care of keeping the current compiled code running, but what about future versions? If I open up the source for one of my applications and attempt to compile, I now receive errors stating "The type or namespace name 'Logger' could not be found." It seems the redirection works at runtime but not at compile time. For someone not familiar with the previous refactoring, this could prove an interesting issue to track down.

In my opinion, there is a far better solution than using the TypeForwardedTo attribute. Going back to the original code, this time I copy the code to the new assembly (as opposed to moving it.) On the copy I change the namespace to match my new assembly.

  namespace LoggingUtilities

  {

      public class Logger

      {

          public void LogError(string message)

          { 

              Debug.WriteLine("Error: " + message);

          }

      }

  }

In my original Logger class, I create an instance of my new Logger. Each method in the original class now forwards requests to the new Logger instance. In this way, I am wrapping the new class in the original. This allows applications to still use the old class, though the functionality has been moved.

  public class Logger

  {

      LoggingUtilities.Logger _logger =

          new LoggingUtilities.Logger();

      [Obsolete("Use LoggingUtilities.Logger instead")]

      public void LogError(string message)

      {

          _logger.LogError(message);

      }

  }

As before we need to evaluate referencing projects. Because our original class still exists, these applications will continue to compile.

Note that I've added an "Obsolete" attribute to the LogError method. This means we will receive a compiler warning (or error) that we need to change our application to use the new class. This makes it clear what needs to be modified, saving time on any rework.

Code can be both clean and efficient

Chapter 26 of Code Complete focuses on code tuning - the art of modifying code to improve performance. One example given is a switched loop:

  for (i = 0; i < count; i++)

  {

      if (sumType == SUMTYPE_NET)

      {

          netSum = netSum + amount[i];

      }

      else

      {

          grossSum = grossSum + amount[i];

      }

  }

Notice the 'if' statement inside the loop. If the array is rather large, this statement will be evaluate numerous times, despite the fact that the result will never change. The recommended solution is to unswitch the loop, so the 'if' statement is only evaluated once:

  if (sumType == SUMTYPE_NET)

  {

      for (i = 0; i < count; i++)

      {

          netSum = netSum + amount[i];

      }

  }

  else

  {

      for (i = 0; i < count; i++)

      {

          grossSum = grossSum + amount[i];

      }

  }

This recommendation was given with one warning: this code is harder to maintain. If the logic for the loops needs to change, you have to make sure to change both loops to match.

As with most coding tasks, there is more than one possible solution. In this case the ideal approach is to have both a single comparison and a single loop. If we throw one additional variable into the code, we can calculate the summation and then add it accordingly:

  for (i = 0; i < count; i++)

  {

      arraySum = arraySum + amount[i];

  }

  if (sumType == SUMTYPE_NET)

  {

      netSum = netSum + arraySum;

  }

  else

  {

      grossSum = grossSum + arraySum;

  }

Export filtered Access data to Excel

In my free time I've been creating an MSAccess database containing a few data-entry forms. One of these forms allows the user to filter records based on several different criteria. This part was relatively straightforward. The difficulty was in trying to export the filtered information to an Excel spreadsheet. Although this functionality exists in Access, the installed help file was less than helpful. Forum posts seemed to contain partial solutions or solve something almost, but not quite what I was trying to do.

The following VBA subroutine is the eventual solution:

Private Sub Export_Click()
    Dim whereClause As String
    
    ' Generate our WHERE clause based on form values
    whereClause = GenerateFilterClause
    
    ' If we have no filter, export nothing
    If IsEmptyString(Nz(whereClause)) Then
        Exit Sub
    End If
    
    Dim query As String
    query = "SELECT DISTINCTROW Contacts.* " & _
            " FROM Contacts " & _
            " INNER JOIN Applications " & _
            " ON Contacts.ContactID = Applications.ContactID " & _
            " WHERE " & whereClause & ";"
    
    Dim filename As String
    filename = "c:\test.xls"

    ' Placeholder query already in the database
    Dim queryName As String
    queryName = "FilterExportQuery"

    ' Update the placeholder with the created query
    CurrentDb.QueryDefs(queryName).SQL = query

    ' Run the export
    DoCmd.TransferSpreadsheet acExport, acSpreadsheetTypeExcel9, queryName, filename
End Sub

Monitoring log files in real time

Debugging Windows services, especially in a test or production environment, can be tricky. In many cases you won't have access to the box. You certainly won't have the ability to step through the code.

Thus, you are usually forced to monitor log files, looking for an indication of where the problem occurred. The typical method is to start by opening the file in Notepad. Then, when you want to see more recent log entries, you close and reopen the file. This is mildly annoying when dealing with a single service. If your business workflow is split among multiple services, this becomes incredibly inefficient.

An easier solution is to use a log monitor app such as BareTail. For this little demo I am using the free version of the tool.

I have three separate services logging to files named "process1.log", "process2.log" and "process3.log." To keep it simple I am only logging the RequestID for each received request. Here I have loaded all three logs into BareTail.


When I send a new request to the system it should update each log file. BareTail monitors the logs and displays any updates. In the screenshot below, note the new Request ID #2918891. Note also that the document tabs for each file show a green arrow - this indicates an update was made.


As you view each tab, the green arrow will be cleared to visually show which files you have already reviewed.


Say you were trying to debug a request that fails to make it through the system. A quick glance at the document tabs will show you how far a request made it through the system. After reviewing each log (to clear the green markers) we submit another request. In the following screenshot, note that we have a green arrow for process1.log and process2.log, but none for process3.log. So either the second process failed to send the message on, or the third process failed to receive it.

Cleaning up enumerations

When working on existing code I occasionally run into an enumeration class similar to this:

  public class PowertoolsConstants

  {

      public enum Powertools

      {

          PowerDrill = 0, // Standard, corded drill

          Chainsaw,       // Everyone's favorite

          CircularSaw     // If the chainsaw is out of gas, use this

      }

      public static Powertools ConvertFromString(string s)

      {

          switch (s)

          {

              case "PowerDrill":

                  return Powertools.PowerDrill;

              case "0":

                  return Powertools.PowerDrill;

              case "Chainsaw":

                  return Powertools.Chainsaw;

              case "1":

                  return Powertools.Chainsaw;

              case "CircularSaw":

                  return Powertools.CircularSaw;

              case "2":

                  return Powertools.CircularSaw;

              default:

                  throw new Exception("Unknown Powertool");

          }

      }

      public static string ConvertFromPowertool(Powertools p)

      {

          switch (p)

          {

              case Powertools.Chainsaw:

                  return "Chainsaw";

              case Powertools.CircularSaw:

                  return "CircularSaw";

              case Powertools.PowerDrill:

                  return "PowerDrill";

              default:

                  return "Unknown";

          }

      }

  }

Nothing too complex, but it can be cleaned up a bit. For starters, accessing the enum currently requires referencing the class:

  PowertoolsConstants.Powertools tool =

      PowertoolsConstants.Powertools.Chainsaw;

If we move the enum declaration above the class we can remove the class reference:

  Powertools tool = Powertools.Chainsaw;

Next is addressing the two methods in the class: ConvertFromString and ConvertFromPowertool. The purpose of these methods is to switch between our enumeration and a string representation of the enum, perhaps to store values in an xml file or database. As the .Net Framework already contains this functionality, the methods are not necessary and can be deleted.

To convert from an enum value to a string we can use Enum.GetName

  string toolName = Enum.GetName(typeof(Powertools), tool);

To convert from a string to an enum value we can use Enum.Parse. Note that this will throw an ArgumentException if an invalid string is passed in.

  tool = (Powertools)Enum.Parse(typeof(Powertools), toolName);

With the two methods removed, the class PowertoolsConstants is empty and can be deleted.

One final thing to look at are the comments beside the enum values. These appear to be usage notes. If a developer using the enum needs to know this information, he shouldn't have to open this code to get it. The way to correct this is to replace the existing comments with xml-style comments.

  public enum Powertools

  {

      /// <summary>

      /// Standard, corded drill

      /// </summary>

      PowerDrill = 0,

      /// <summary>

      /// Everyone's favorite

      /// </summary>

      Chainsaw,

      /// <summary>

      /// If the chainsaw is out of gas, use this

      /// </summary>

      CircularSaw

  }

Doing this will provide the developer with Intellisense hints as they code:

Parameterized tests in NUnit

In an earlier post I showed how to pass parameters to test methods using an NUnit RowTest extension. As of version 2.5, the extensions are no longer packaged with the NUnit installer. The good news is that the addition of parameterized tests replaces the RowTest and adds a number of new features as well.

For reference, my previous RowTest looked like this:

[RowTest]

[Row(2, 3)]

[Row(-1, -4)]

public void AddTwoNumbers(int x, int y)

{

    Assert.AreEqual(x + y, Add(x, y),

        "Add returned incorrect result");

}

A basic switch to a parameterized test is a matter of dropping the RowTest attribute and replacing each Row attribute with a similarly-formatted TestCase attribute. The new code, which creates two distinct tests as before, looks like this:

[TestCase(2, 3)]

[TestCase(-1, -4)]

public void AddTwoNumbers(int x, int y)

{

    Assert.AreEqual(x + y, Add(x, y),

        "Add returned incorrect result");

}

In addition to single parameters you can now specify ranges. If I want to test values of X from 1 to 5, with a Y value of 1, I can do so using the Range and Values attributes, like so:

[Test]

public void AddTwoNumbers(

                    [Range(1, 5)]int x,

                    [Values(1)]int y)

{

    Assert.AreEqual(x + y, Add(x, y),

        "Add returned incorrect result");

}        

In the test runner, this shows up as five distinct unit tests


If I specify the range 1-5 for both X and Y, NUnit defaults to creating 25 unique tests. This is the default Combinatorial attribute.


If I wish to use a value from each range only once, I instead mark the test as Sequential

[Test, Sequential]

public void AddTwoNumbers(

                    [Range(1, 5)]int x,

                    [Range(1, 5)]int y)

{

    Assert.AreEqual(x + y, Add(x, y),

        "Add returned incorrect result");

}        

which produces the desired effect