Define a record type in PL/SQL block that references a collection of itself

Question

How to define a record type in PL/SQL anonymous block that contains a property that is a collection of itself? Look at the following example:

DECLARE
    type t_item is record (
        name varchar2(64),
        children t_items              -- referencing t_items type
    );
    type t_items is table of t_item;  -- referencing t_item type

BEGIN
    -- script code
END

PL/SQL has no type hoisting so Oracle engine raises an exception:

PLS-00498: illegal use of a type before its declaration

How to define a record t_item that contains a table of t_item in its property children?

Answer 1

You can use objects defined in the SQL Scope using inheritance:

SQL Fiddle

Oracle 11g R2 Schema Setup:

CREATE TYPE abstract_item IS OBJECT (
  name VARCHAR2(64)
) NOT FINAL NOT INSTANTIABLE
/

CREATE TYPE t_items IS TABLE OF abstract_item
/

CREATE TYPE t_item UNDER abstract_item (
  children t_items
) INSTANTIABLE
/

Query 1:

SELECT t_item(
         '1',
         t_items(
           t_item( '1.1', t_items() ),
           t_item(
             '1.2',
             t_items(
               t_item( '1.2.1', null )
             )
           ),
           t_item( '1.3', null )
         )
       )
FROM   DUAL

Results: (SQLFiddle doesn't display it nicely - but it runs without errors)

| T_ITEM('1',T_ITEMS(T_ITEM('1.1',T_ITEMS()),T_ITEM('1.2',T_ITEMS(T_ITEM('1.2.1',NULL))),T_ITEM('1.3',NULL))) |
|-------------------------------------------------------------------------------------------------------------|
|                                                                                  oracle.sql.STRUCT@2a094aab |

You could use a similar declaration in PL/SQL:

DECLARE
  items t_item;
BEGIN
  items = t_item( 'Item Name', t_items( /* ... */ ) );
END;
/