Single or Stand-alone table (part 7)

 This brings up to the Delete Procedure, and the DeleteValidate Procedure. These we will explain in this post.

Just as the Save Procedure call a Validate Procedure, so the Delete Procedure call a DeleteValidate Procedure.   In this manner you can easily insert code to ensure the record being deleted is not being "used" or referenced elsewhere in your application. The Delete itself is very straight forward.

  Procedure.i Delete(*Class.FighterSize)
    Protected Result, DBID 
    Protected Sql$ 
    If DeleteValidate(*Class) = #False 
      ProcedureReturn #False 
    Else 
      DBID = DB::Open(DBTYPE::#Sqlite)
      SetDatabaseLong(DBID, 0, *Class\ID) 
      Sql$ = " DELETE "
      Sql$ = Sql$ + "FROM "
      Sql$ = Sql$ + "FighterSize "
      Sql$ = Sql$ + "WHERE "
      Sql$ = Sql$ + "ID = ?  "
      Result = DB::Update(DBID, Sql$) 
      DB::Close(DBID) 
    ProcedureReturn Result 
  EndIf

If the Record is approved for deletion, we open the Database with a call to our DB Module, Create the Delete SQL. Then Call the Update query Procedure or our DB Module, Close the Database and return the Results of our SQL Query.


The DeleteValidation procedure is very Custom to the application. Only you know how the data layer is built and what records are in use where. So Here I will give you examples of how this module can be written.

Here is a default shell, which tests nothing, simply returns that the record in question is valid to be deleted.

  Procedure.i DeleteValidate(*Class.FighterSize)
    Protected DBID, Sql$, Cnt, PassFail, ErrMsg.s 
    PassFail.i = #True 
    ErrMsg.s = ""
    ;Validation SQL goes here
    If PassFail= #False
      THEMEDMESSAGE::MessageBox("Error", ErrMsg) 
    EndIf
    ProcedureReturn PassFail 
  EndProcedure

In this example I'll make a check against another table to ensure that the Fighter in question has not already been assigned to a carrier. If has, then the record must first be removed from the Carrier Before it can be deleted.

  
  Procedure.i DeleteValidate(*Class.FighterSize)
    Protected DBID, Sql$, Cnt, PassFail, ErrMsg.s 
    PassFail.i = #True 
    ErrMsg.s = ""
    DBID = DB::Open(DBTYPE::#Sqlite)
    SetDatabaseLong(DBID, 0, *Class\ID) 
    Sql$ = "SELECT 
    Sql$ = Sql$ + "Name"
    Sql$ = Sql$ + "FROM "
    Sql$ = Sql$ + "Carrier "
    Sql$ = Sql$ + "WHERE "
    Sql$ = Sql$ + "FighterSizeID = ? "
    If DB::Query(DBID, Sql$) 
      While NextDatabaseRow(DBID)  
        Cnt.c =  GetDatabaseLong(DBID, 0)  
        If Cnt > 0  
          PassFail= #False  
          ErrMsg= "Fighter Size in use in Carrier: "+GetDatabaseString(DBID, DatabaseColumnIndex(DBID,"Name")) 
        EndIf  
      Wend  
    EndIf
    DB::Close(DBID) 
    If PassFail= #False
      THEMEDMESSAGE::MessageBox("Error", ErrMsg) 
    EndIf
    ProcedureReturn PassFail 
  EndProcedure

The DeleteValidate Procedure has the Job to ensure that the record can be deleted, but it also has the job to report to the user why it cannot be deleted. this is simply achieved by displaying a message detailing the reason the record cannot be deleted.


    If PassFail= #False
      THEMEDMESSAGE::MessageBox("Error", ErrMsg) 
    EndIf

once this has been completed, he simply returns the result of his findings back to the Delete Procedure.




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