Question

Is it possible to do a select directly into a hierarchical user type?

Imagine a table structure like this:

PARENT
------
ID
NAME

CHILD
-----
ID
PARENT_ID
NAME

Additionally, I have user types like this:

create or replace type child_item as object
(
  ID NUMBER(10),
  NAME VARCHAR(255)
);

create or replace type children_table as table of child_item;

create or replace type parent_item as object
(
  ID NUMBER(10),
  NAME VARCHAR(255),
  CHILDREN CHILDREN_TABLE
);

create or replace type parent_table as table of parent_item;

And a statement like this:

select * from parent p inner join child c on p.id = c.parent_id;

Now, I want the result of that statement to be in an object of type parent_table. Is this somehow possible without the use of a complex FOR loop?

Answer 1

You can use COLLECT:

SELECT parent_item(p.ID, 
                   p.NAME, 
                   CAST(COLLECT(child_item(c.id, c.NAME)) AS children_table))
  FROM PARENT p
 INNER JOIN child c ON p.id = c.parent_id
 GROUP BY p.ID, p.NAME

This will return a list of PARENT_ITEM that you can BULK COLLECT into a PARENT_TABLE.

You could use COLLECT again in an outer query to get a PARENT_TABLE directly:

SELECT CAST(COLLECT(parents) AS parent_table)
  FROM (SELECT parent_item(p.ID, 
                           p.NAME, 
                           CAST(COLLECT(child_item(c.id, c.NAME)) 
                             AS children_table)
                          ) parents
          FROM PARENT p
         INNER JOIN child c ON p.id = c.parent_id
         GROUP BY p.ID, p.NAME)