oracle Form Builer:ID_NULL Built-in

Description                                                                    
Returns a BOOLEAN value that indicates whether the object ID is available.
Syntax                                                                        
FUNCTION ID_NULL(Alert ALERT);
FUNCTION ID_NULL(Block BLOCK);
FUNCTION ID_NULL(Canvas CANVAS);
FUNCTION ID_NULL(Editor EDITOR);
FUNCTION ID_NULL(FormModule FORMMODULE);
FUNCTION ID_NULL(GroupColumn GROUPCOLUMN);
FUNCTION ID_NULL(Item ITEM);
FUNCTION ID_NULL(LOV LOV);
FUNCTION ID_NULL(MenuItem MENUITEM);
FUNCTION ID_NULL(ParamList PARAMLIST);
FUNCTION ID_NULL(RecordGroup RECORDGROUP);
FUNCTION ID_NULL(Relation RELATION);
FUNCTION ID_NULL(Report_Object REPORT_OBJECT);
FUNCTION ID_NULL(TabPage TABPAGE);
FUNCTION ID_NULL(Timer TIMER);
FUNCTION ID_NULL(Viewport VIEWPORT);
FUNCTION ID_NULL(VisualAttribute VISUALATTRIBUTE);
FUNCTION ID_NULL(Window WINDOW);
Built-in Type unrestricted function
Returns BOOLEAN
Enter Query Mode yes

Parameters                                                         
object_id You can call this function to test results of the following object ID types:

• Alert
• Block
• Canvas
• Editor
• FormModule
• GroupColumn
• Item
• LOV
• MenuItem
• ParamList
• RecordGroup
• Relation
• REPORT_OBJECT
• TabPage
• Timer
• Viewport
• VisualAttribute
• Window

Usage Notes                                                  
Use ID_NULL when you want to check for the existence of an object created dynamically at runtime. For example, if a specific record group already exists, you will receive an error message if you try to create that record group. To perform this check, follow this general process:

• 　　Use the appropriate FIND_ built-in to obtain the object ID.
• 　　Use ID_NULL to check whether an object with that ID already exists.
• 　　If the object does not exist, proceed to create it.

      If you are going to test for an object’s existence at various times (that is, more than once during a run), then you need to reissue the appropriate FIND_ every time -- once preceding each use of ID_NULL.

ID_NULL Examples                                        

 /*** Built-in: CREATE_GROUP ** Example: Creates a record group and populates its values ** from a query. */
DECLARE
  rg_name VARCHAR2(40) := 'Salary_Range';
  rg_id   RecordGroup;
  gc_id   GroupColumn;
  errcode NUMBER;
BEGIN
  /* ** Make sure the record group does not already exist.*/
  rg_id := Find_Group(rg_name); /* ** If it does not exist, create it and add the two ** necessary columns to it. */
  IF Id_Null(rg_id) THEN
    rg_id := Create_Group(rg_name); /* Add two number columns to the record group */
    gc_id := Add_Group_Column(rg_id, 'Base_Sal_Range', NUMBER_COLUMN);
    gc_id := Add_Group_Column(rg_id, 'Emps_In_Range', NUMBER_COLUMN);
  END IF; /* ** Populate group with a query */
  errcode := Populate_Group_With_Query(rg_id,
                                       'SELECT SAL-MOD(SAL,1000),COUNT(EMPNO) ' ||
                                       'FROM EMP ' ||
                                       'GROUP BY SAL-MOD(SAL,1000) ' ||
                                       'ORDER BY 1');
END;