Oracle PL/SQL How to create list of lists - oracle

Question

in python we create complex arrays like :
[['element1',['element2',['element3'],
['element1',['element2',['element3'],
['element1',['element2',['element3']]
is there anyway to do that in PL/SQL?

Answer 1

You can use inheritance with Oracle types to have multiple nested collections:
Oracle Setup:
CREATE TYPE collect_abstract_type IS OBJECT(
isCollection NUMBER(1,0),
MEMBER FUNCTION toString RETURN CLOB
) NOT FINAL NOT INSTANTIABLE
/
CREATE TYPE collect_element_type UNDER collect_abstract_type (
value VARCHAR2(20),
OVERRIDING MEMBER FUNCTION toString
RETURN CLOB,
CONSTRUCTOR FUNCTION collect_element_type(value VARCHAR2)
RETURN SELF AS RESULT
)
/
CREATE TYPE BODY collect_element_type AS
OVERRIDING MEMBER FUNCTION toString
RETURN CLOB
IS
BEGIN
RETURN '"' || SELF.value || '"';
END;
CONSTRUCTOR FUNCTION collect_element_type(value VARCHAR2)
RETURN SELF AS RESULT
IS
BEGIN
SELF.isCollection := 0;
SELF.value := value;
RETURN;
END;
END;
/
CREATE OR REPLACE TYPE collect_abstract_type_table IS TABLE OF collect_abstract_type
/
CREATE TYPE collect_list_type UNDER collect_abstract_type (
items collect_abstract_type_table,
OVERRIDING MEMBER FUNCTION toString
RETURN CLOB,
CONSTRUCTOR FUNCTION collect_list_type
RETURN SELF AS RESULT,
CONSTRUCTOR FUNCTION collect_list_type(items collect_abstract_type_table)
RETURN SELF AS RESULT
)
/
CREATE TYPE BODY collect_list_type AS
OVERRIDING MEMBER FUNCTION toString
RETURN CLOB
IS
p_string CLOB;
p_first BOOLEAN := TRUE;
BEGIN
p_string := '[';
FOR i IN 1 .. SELF.items.count LOOP
IF p_first THEN
p_first := FALSE;
ELSE
p_string := p_string || ',';
END IF;
IF SELF.items(i) IS NULL THEN
p_string := p_string || 'NULL';
ELSE
p_string := p_string || SELF.items(i).toString;
END IF;
END LOOP;
p_string := p_string || ']';
RETURN p_string;
END;
CONSTRUCTOR FUNCTION collect_list_type
RETURN SELF AS RESULT
IS
BEGIN
SELF.isCollection := 1;
SELF.items := collect_abstract_type_table();
RETURN;
END;
CONSTRUCTOR FUNCTION collect_list_type(items collect_abstract_type_table)
RETURN SELF AS RESULT
IS
BEGIN
SELF.isCollection := 1;
IF items IS NULL THEN
SELF.items := collect_abstract_type_table();
ELSE
SELF.items := items;
END IF;
RETURN;
END;
END;
/
Then you could do something like:
SELECT collect_list_type(
collect_abstract_type_table(
collect_element_type( 'Element1' ),
collect_list_type(
collect_abstract_type_table(
collect_element_type( 'Element2' ),
collect_list_type()
)
),
NULL,
collect_element_type( 'Element4' )
)
).toString() AS list
FROM DUAL;
Which outputs:
LIST
--------------------------------------------
["Element1",["Element2",[]],NULL,"Element4"]