There are 3 techniques that can be used to be able to preserve custom
source code across source code generations of the mapping tool,
depending on the version of VBSF:


I. Version 2.2 supports the preservation of existing code via
the PRESERVED_CODE tag.

   Changes to the source code of existing classes can be
   preserved from generation to generation by means of the new
   %PRESERVED_CODE% tag. This tag must be placed in 2 places:

   1. In the template file to specify where the preserved source code block
      should be placed. See the template4.tmpl file in the samples schrepository
      directory.

   2. In the actual source code inside comments to delimit the preserved code.
      For example:
         
      /* PRESERVED_CODE */
  
      custom code is here, including additional non-persistent attributes,
      methods, static variables and methods, constructors, comments, etc.
    
      /* PRESERVED_CODE */

      Note that only one PRESERVED_CODE code block is allowed per class.



II. In v2.1x and below, a technique of extending the generated classes can be used.
To do this, use the following procedure:

   1. Change the source template to add a suffix or prefix to the package name. For
      example, starting with the package declaration line below:


         package %PACKAGE_NAME%;

      add a suffix to it as shown below:

         package %PACKAGE_NAME%.data;

      or add a prefix to it as shown below:

         package generated.%PACKAGE_NAME%;

	
      If, for example, the persistent classes defined in the mapping tool belong to
      the 'com.mycompany' package, then with the above suffix modification the mapping
      tool would generate classes as shown below:

         
         package com.mycompany.data;

         public class Customer {
            /* persistent attributes */
            /* accessors & mutators */
         }



      And with the prefix modification the mapping tool would generate classes as
      shown below:

         package generated.com.mycompany;

         public class generated.com.mycompany.Customer {
            /* persistent attributes */
            /* accessors & mutators */
         }


   2. Manually create your class as a subclass of the generated class using the same
      package name as defined in the mapping tool and put all the additional logic.
      In the case where a suffix was added, then your subclass would be defined as
      shown below:


         package com.mycompany;

         public class Customer extends com.mycompany.data.Customer {
            /* additional non-persistent attributes and logic methods go here */
         }

  

   The VBSF runtime will persist your subclasses, and you can regenerate the generated
   classes as many times as you want without overwriting your own subclasses. Also note
   that all persistent attributes should be defined as protected so they can be accessed
   by your subclasses.


III. The last technique is demonstrated in the vposdemo2 sample application. It is also
based on extending a persistent base class, but requires both the subclass and the superclass
to be defined in the mapping tool. For details, see the Invoice and InvoiceLine classes in
the vposdemo2 sample application.


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