Kill Objects

In "normal" applications, objects are only deleted logically (see statement DeleteObject). This may create references from a logically deleted object to a "vital" one, but it won't create any relations leading into "nowhere" and causing an error.

Objects need to be removed physically from the database outside the application. The following tools might help here:

• the object Cross-Reference provides the information, whether any other object refers to the object, which is about to be deleted
  

• the object manager functions CollectOrphans() and CollectOrphans2() collect objects, which can be deleted due to cross-reference tests.

Two ways of removing an object from the database:

• Variant 1 - the amount of objects to be deleted is known:

  Var(obsoleteObjects, objectsToKillSafely)  
  
  .  .  .  // determine objects to be deleted
  -> obsoleteObjects 
  
  obsoleteObjects "objects.xrf" GetManager(OBJECT) Call(CollectOrphans2) 
  -> objectsToKillSafely
  
  .  .  . // display in ObjectList for checking purposes
  
  objectsToKillSafely iterate { KillObject }
  
  This requires the object cross-reference created with cxxosr.exe, which can be either established across the entire database, or -to save time- only partially for the objects to be deleted (see partial cross-reference). The parameter file for the partial cross-reference can be generated as follows:   
   
  "xobjects.lst" obsoleteObjects GetManager(OBJECT) Call(GetDBUtility) Call(PartialXRefParams) 
  The function CollectOrphans2() removes all objects from the predetermined collection, that are referenced directly or indirectly by a vital object. The remaining objects can be deleted physically, without causing faulty references. The CollectOrphans2() works iterative (see picture). 
  
  
  

• Variant 2 - determine all objects that can be potentially deleted: Flag /O claims that a corresponding CX_XREF object is created for every database object. Even for the ones that can't be accessed anymore. With this information, it is possible to identify objects which can be deleted physically:
   

  Var(mode, objectsToKillSafely)
  
  TRUE -> mode  // also consider objects that are not deleted logically
  FALSE -> mode // consider only objects, that have been deleted logically
  
  mode "xobjects.xrf" GetManager(OBJECT) Call(CollectOrphans)
  -> objectsToKillSafely
  
  First, the function CollectOrphans() generates a primary set of objects, which is either not referenced at all, or only by logically deleted objects. After, all those objects are searched for, which are referenced by an object outside the set. These objects are removed from the set, and this step is repeated. This iteration cycle stops, when there are no more objects, which are referenced by objects outside the current set (see picture for CollectOrphans2).