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A Little Chat About Code Sensible Code Generation

By , 9 Apr 2009
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At work we all try and do our best to be productive. And as software developers we all probably have to author classes, that follow a familiar pattern. So if like me you are looking to work smart, you will undoubtedly look into code that writes code.

This is good in my opinion, code generation can save a LOT of time. But the cardinal rule of clever code generation is never ever having to touch the generated code once it has been generated. If you do have to make changes by hand to a generated file, its all wrong and the entire process can no longer be trusted.

Now this perplexed me for a while as I had a very real demand to perform some calculations when a property changes. Now this would be cool and could possibly be made part of the generated code if you know about it in advance and have the correct knowledge to instruct your code generator about this in advance. We neither knew about these requirements up front or were able to build enough intelligence into our code generator to deal with this sort of this.

So you can imagine that our business analyst came along and said "when property X changes, use property Y and Z to work out Q". Mmmmm.

This would require me to do something when a property changes, this would mean manually changing my auto generated code. Oh no.

So I had a think about this, and luckily C# being the lovely language that it is has the answers. Partial classes / methods. All we need to do is provide the stubs in the generated code portion and provide hooks that the manually created partial class can use.

Here is an example.

The code generated part

   1:  using System;
   2:  using System.Collections.Generic;
   3:  using System.Linq;
   4:  using System.Text;
   5:  
   6:  namespace NiceCodeGenStylee
   7:  {
   8:      public partial class Class1
   9:      {
  10:  
  11:          private Int32 number1 = 0;
  12:          private Int32 number2 = 0;
  13:  
  14:          /// <span class="code-SummaryComment"><summary></span>
  15:          /// When this method in called the hand cranked 
  16:          /// code should have the implementation
  17:          /// <span class="code-SummaryComment"></summary></span>
  18:          partial void Number1PropertyChanging(
                            IntReportChanges args);
  19:  
  20:          /// <span class="code-SummaryComment"><summary></span>
  21:          /// When this method in called the hand cranked 
  22:          /// code should have the implementation
  23:          /// <span class="code-SummaryComment"></summary></span>
  24:          partial void Number1CodePropertyChanged(
                            Int32ItemChanges args);
  25:  
  26:  
  27:          /// <span class="code-SummaryComment"><summary></span>
  28:          /// When this method in called the hand cranked 
  29:          /// code should have the implementation
  30:          /// <span class="code-SummaryComment"></summary></span>
  31:          partial void Number2PropertyChanging(
                            IntReportChanges args);
  32:  
  33:          /// <span class="code-SummaryComment"><summary></span>
  34:          /// When this method in called the hand cranked 
  35:          /// code should have the implementation
  36:          /// <span class="code-SummaryComment"></summary></span>
  37:          partial void Number2CodePropertyChanged(
                            Int32ItemChanges args);
  38:  
  39:  
  40:          /// <span class="code-SummaryComment"><summary></span>
  41:          /// Number1 property
  42:          /// <span class="code-SummaryComment"></summary></span>
  43:          public Int32 Number1
  44:          {
  45:              get { return number1; }
  46:              set
  47:              {
  48:                  //is it different
  49:                  if(value != number1)
  50:                  {
  51:                      Int32 oldValue = number1;
  52:  
  53:                      //what are the changes
  54:                      Int32ItemChanges possibleValueChanges
  55:                          = new Int32ItemChanges(
                                      oldValue, value);
  56:  
  57:                      //report the possible change, allows non generated file to 
  58:                      //respond to the change, or cancel it
  59:                      IntReportChanges changes =
  60:                          new IntReportChanges
  61:                          {
  62:                              Values = possibleValueChanges
  63:                          };
  64:                      Number1PropertyChanging(changes);
  65:  
  66:                      //if there was no cancellation
  67:                      if (!changes.Cancel)
  68:                      {
  69:                          number1 = value;
  70:                          //report the change, allows non generated file to 
  71:                          //respond to the change
  72:                          Number1CodePropertyChanged(
                                   possibleValueChanges);
  73:                      }
  74:                  }
  75:  
  76:              }
  77:          }
  78:  
  79:          /// <span class="code-SummaryComment"><summary></span>
  80:          /// Number2 property
  81:          /// <span class="code-SummaryComment"></summary></span>
  82:          public Int32 Number2
  83:          {
  84:              get { return number2; }
  85:              set
  86:              {
  87:                  //is it different
  88:                  if (value != number2)
  89:                  {
  90:                      Int32 oldValue = number2;
  91:  
  92:                      //what are the changes
  93:                      Int32ItemChanges possibleValueChanges
  94:                          = new Int32ItemChanges(oldValue, value);
  95:  
  96:                      //report the possible change, allows non generated file to 
  97:                      //respond to the change, or cancel it
  98:                      IntReportChanges changes =
  99:                          new IntReportChanges
 100:                          {
 101:                              Values = possibleValueChanges
 102:                          };
 103:                      Number1PropertyChanging(changes);
 104:  
 105:                      //if there was no cancellation
 106:                      if (!changes.Cancel)
 107:                      {
 108:                          number2 = value;
 109:                          //report the change, allows non generated file to 
 110:                          //respond to the change
 111:                          Number1CodePropertyChanged(
                                   possibleValueChanges);
 112:                      }
 113:                  }
 114:  
 115:              }
 116:          }
 117:  
 118:  
 119:      }
 120:  }

Where the manually created code part, can use these partial method stubs to do calculations when a property changes or even cancel a changing property based on some condition.

   1:  using System;
   2:  using System.Collections.Generic;
   3:  using System.Linq;
   4:  using System.Text;
   5:  
   6:  namespace NiceCodeGenStylee
   7:  {
   8:      partial class Class1
   9:      {
  10:          /// <span class="code-SummaryComment"><summary></span>
  11:          /// When this method in called the hand cranked 
  12:          /// code should have the implementation
  13:          /// <span class="code-SummaryComment"></summary></span>
  14:          partial void Number2PropertyChanging(
                   IntReportChanges args)
  15:          {
  16:              if (args.Values.NewValue == 0)
  17:              {
  18:                  Console.WriteLine(
  19:                      "Number2 is invalid value, cancelling");
  20:                  args.Cancel = true;
  21:              }
  22:          }
  23:  
  24:          /// <span class="code-SummaryComment"><summary></span>
  25:          /// When this method in called the hand cranked 
  26:          /// code should have the implementation
  27:          /// <span class="code-SummaryComment"></summary></span>
  28:          partial void Number2CodePropertyChanged(
                   Int32ItemChanges args)
  29:          {
  30:              Console.WriteLine(String.Format(
  31:                  "Number2 changed to {0}, doing calcs", 
                       args.NewValue));
  32:              DoNumberCalcs();
  33:          }
  34:  
  35:  
  36:          /// <span class="code-SummaryComment"><summary></span>
  37:          /// When this method in called the hand cranked 
  38:          /// code should have the implementation
  39:          /// <span class="code-SummaryComment"></summary></span>
  40:          partial void Number1PropertyChanging(
                   IntReportChanges args)
  41:          {
  42:              if (args.Values.NewValue == 0)
  43:              {
  44:                  Console.WriteLine(
  45:                      "Number1 is invalid value, cancelling");
  46:                  args.Cancel = true;
  47:              }
  48:          }
  49:  
  50:          /// <span class="code-SummaryComment"><summary></span>
  51:          /// When this method in called the hand cranked 
  52:          /// code should have the implementation
  53:          /// <span class="code-SummaryComment"></summary></span>
  54:          partial void Number1CodePropertyChanged(
                   Int32ItemChanges args)
  55:          {
  56:              Console.WriteLine(String.Format(
  57:                  "Number1 changed to {0}, doing calcs", 
                       args.NewValue));
  58:              DoNumberCalcs();
  59:          }
  60:  
  61:  
  62:          private void DoNumberCalcs()
  63:          {
  64:              Console.WriteLine(
  65:                  String.Format("Number1 ({0}) + Number2 ({1}) ={2}",
  66:                      number1, number2, number1 + number2));
  67:          }
  68:      }
  69:  }

Where these little helper classes are used

   1:  using System;
   2:  using System.Collections.Generic;
   3:  using System.Linq;
   4:  using System.Text;
   5:  
   6:  namespace NiceCodeGenStylee
   7:  {
   8:      struct Int32ItemChanges
   9:      {
  10:          public readonly Int32 OldValue;
  11:          public readonly Int32 NewValue;
  12:  
  13:          public Int32ItemChanges(
                   Int32 oldValue, Int32 newValue)
  14:          {
  15:              OldValue = oldValue;
  16:              NewValue = newValue;
  17:          }
  18:      }
  19:  
  20:  }
   1:  using System;
   2:  using System.Collections.Generic;
   3:  using System.Linq;
   4:  using System.Text;
   5:  
   6:  namespace NiceCodeGenStylee
   7:  {
   8:      class IntReportChanges
   9:      {
  10:          public Int32ItemChanges Values { get; set; }
  11:          public Boolean Cancel { get; set; }
  12:      }
  13:  }

And here is a demo of it running

image-thumb6.png

See it all works lovely.

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

About the Author

Sacha Barber
Software Developer (Senior)
United Kingdom United Kingdom
I currently hold the following qualifications (amongst others, I also studied Music Technology and Electronics, for my sins)
 
- MSc (Passed with distinctions), in Information Technology for E-Commerce
- BSc Hons (1st class) in Computer Science & Artificial Intelligence
 
Both of these at Sussex University UK.
 
Award(s)

I am lucky enough to have won a few awards for Zany Crazy code articles over the years

  • Microsoft C# MVP 2014
  • Codeproject MVP 2014
  • Microsoft C# MVP 2013
  • Codeproject MVP 2013
  • Microsoft C# MVP 2012
  • Codeproject MVP 2012
  • Microsoft C# MVP 2011
  • Codeproject MVP 2011
  • Microsoft C# MVP 2010
  • Codeproject MVP 2010
  • Microsoft C# MVP 2009
  • Codeproject MVP 2009
  • Microsoft C# MVP 2008
  • Codeproject MVP 2008
  • And numerous codeproject awards which you can see over at my blog

Comments and Discussions

 
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