Building an object of nested table types

Question

Hi,
Looking for suggestions for the following.
I have a procedure with 4 table types.
They are in a hierarchical order so that 4 is the child of 3, 3 is the child of 2 and 2 is the child of 1.
One of the columns of table 1 is a table type holding all the child records from table 2,
One of the columns of table 2 is a table type holding all the child records from table 3,
One of the columns of table 3 is a table type holding all the child records from table 4,
I have 4 cursors that pull out all of the data to populate each of my 4 table types.
I am trying to figure out how to nest my fetches to populate all of my table types to create a single object that hold all of my data.
It’s a table of a table of a table of a table.
Column 3 of table 1 holds table 2
Column 3 of table 2 holds table 3
Column 3 of table 3 holds table 4
I’ve tried creating my procedure like this (pseudo code)
declare
tab_1 tab_1_type;
tab_2 tab_2_type;
tab_3 tab_3_type;
tab_4 tab_4_type;
cursor get_tab_1 is
select col1, col2, tab_2 – added the table type for the child records
from data_table_1
cursor get_tab_2(tab_1_pk in number) is
select col1, col2, tab_3 – added the table type for the child records
from data_table_2
where tab_2_fk = tab_1_pk
cursor get_tab_3(tab_2_pk in number) is
select col1, col2, tab_4 – added the table type for the child records
from data_table_3
where tab_3_fk = tab_2_pk
cursor get_tab_4(tab_3_pk in number) is
select col1, col2, col3
from data_table_4
where tab_4_fk = tab_3_pk
begin
open get_tab_1;
loop
open get_tab_2
loop
open get_tab_3
loop
open get_tab_4(tab_3_pk);
bulk collect get_tab_4 into tab_4;
close get_tab_4;
fetch get_tab_3 into tab_3;
tab_4:= null;
exit when get_tab_3 %notfound;
end loop;
close get_tab_3;
fetch get_tab_2 into tab_2;
tab_3:= null;
exit when get_tab_2 %notfound;
end loop;
close get_tab_2;
fetch get_tab_1 into tab_1;
tab_3:= null;
exit when get_tab_1 %notfound;
end loop;
close get_tab_1;
l_return := tab_1;
end;
The above won’t work because once the cursor is opened the child tables will be assigned values of null before they have had a chance to populate from the nested fetches.
It’s almost as if I need to execute the fetch and update the extra columns afterwards somehow, something like:
fetch get_tab_3 into tab_3;
tab_3.col3 := tab_4;
tab_4 := null;
end loop;
close get_tab_3;
can I do that?
Also the above seems very cumbersome. If there is a more elegant way of building up this object I’d like to hear it.
Cheers
Yog

Answer 1

Interesting little exercise getting a 3 deep nested structure using a single SQL. Below is my attempt. You should be able to run it in any schema that has CREATE TYPE privs.
SQL> -- Nested structure design:
SQL> --
SQL> -- USER LIST = (
SQL> -- (USER1,OBJECT_LIST1).., (USERn,OBJECT_LISTn)
SQL> -- )
SQL> --
SQL> -- LIST OF OBJECTS = (
SQL> -- (TYPE1, NAME_LIST1).., (TYPEn, NAME_LISTn)
SQL> -- )
SQL> --
SQL> -- LIST OF NAMES = ( NAME1..,NAMEn )
SQL>
SQL>
SQL> create or replace type TObjectList is table of varchar2(50)
2 /
Type created.
SQL>
SQL> create or replace type TObjType is object(
2 obj_type varchar2(50),
3 obj_list TObjectList
4 );
5 /
Type created.
SQL>
SQL> create or replace type TObjTypeList is table of TObjType;
2 /
Type created.
SQL>
SQL> create or replace type TUser is object(
2 user_name varchar2(50),
3 objects TObjTypeList
4 );
5 /
Type created.
SQL>
SQL> create or replace type TUserList is table of TUser;
2 /
Type created.
SQL>
SQL> col NESTED_STRUCTURE format a100
SQL>
SQL> -- constructing the above user list (have made the start of the USER bold in the output below)
SQL> select
2 CAST( COLLECT(
3 TUser(
4 username,
5 CAST( MULTISET(
6 select
7 TObjType(
8 object_type,
9 CAST( COLLECT(o.object_name) as TObjectList)
10 )
11 from all_objects o
12 where o.owner = u.username
13 group by
14 o.object_type
15 ) as TObjTypeList
16 )
17 )
18 ) as TUserList
19 ) as NESTED_STRUCTURE
20 from all_users u
21 where u.username in ('BILLY','DBSNMP')
22 /
NESTED_STRUCTURE(USER_NAME, OBJECTS(OBJ_TYPE, OBJ_LIST))
TUSERLIST(TUSER('BILLY', TOBJTYPELIST(TOBJTYPE('FUNCTION', TOBJECTLIST('GETEMP', 'GETEMP2', 'TESTRET
URN', 'WTF', 'ANOOP_REF')), TOBJTYPE('INDEX', TOBJECTLIST('PK_DEPT', 'PK_EMP')), TOBJTYPE('PROCEDURE
', TOBJECTLIST('USESEQ1', 'FOOPROC', 'W')), TOBJTYPE('TABLE', TOBJECTLIST('X', 'LOAD_TABLE', 'DEPT',
'EMP', 'BONUS', 'SALGRADE')), TOBJTYPE('TYPE', TOBJECTLIST('TEMP', 'TEMPLOYEE', 'TX', 'TARRAY2D', '
TARRAY1D', 'TARRAY3D', 'TOBJECT', 'TOBJTYPE', 'TOBJECTLIST', 'TOBJTYPELIST', 'TUSER', 'TUSERLIST', '
SYSTPTkQoC5hBR+DgQPsKOl0PFQ==', 'SYSTPTkQoC5hyR+DgQPsKOl0PFQ==', 'SYSTPTkQoC5qzR+DgQPsKOl0PFQ==', 'S
YSTPTkQoC5raR+DgQPsKOl0PFQ==')))), TUSER('DBSNMP', TOBJTYPELIST(TOBJTYPE('INDEX', TOBJECTLIST('MGMT_
DB_FILE_GTT_PK', 'MGMT_DB_SIZE_GTT_PK')), TOBJTYPE('PACKAGE', TOBJECTLIST('MGMT_RESPONSE')), TOBJTYP
E('PACKAGE BODY', TOBJECTLIST('MGMT_RESPONSE')), TOBJTYPE('SEQUENCE', TOBJECTLIST('MGMT_RESPONSE_CAP
TURE_ID', 'MGMT_RESPONSE_SNAPSHOT_ID')), TOBJTYPE('TABLE', TOBJECTLIST('MGMT_SNAPSHOT', 'MGMT_SNAPSH
OT_SQL', 'MGMT_BASELINE', 'MGMT_BASELINE_SQL', 'MGMT_CAPTURE', 'MGMT_CAPTURE_SQL', 'MGMT_RESPONSE_CO
NFIG', 'MGMT_LATEST', 'MGMT_LATEST_SQL', 'MGMT_HISTORY', 'MGMT_HISTORY_SQL', 'MGMT_TEMPT_SQL', 'MGMT
DBFILE_GTT', 'MGMT_DB_SIZE_GTT')), TOBJTYPE('VIEW', TOBJECTLIST('MGMT_RESPONSE_BASELINE')))))
SQL>
PS. To understand how the SQL works, run it from the inside out - i.e. run the innermost select on its own to see the output and then add to it until the full select is reached.