Populating application constant values using context namespaces

Question

I have a table like below:
SQL> SELECT * FROM my_constants;
CONSTANT_ID CONSTANT_O CONSTANT_N CONSTANT_V CONSTANT_T CONSTANT_MODULE       SOURCE_ID
      10252 CONSTANT1  CONSTANT1  5000       NUMBER(10) MODULE1                       1
      10253 CONSTANT2  CONSTANT2  5001       NUMBER(10) MODULE2                       1
      10254 CONSTANT1  CONSTANT1  6000       NUMBER(10) MODULE1                       2
      10255 CONSTANT2  CONSTANT2  6001       NUMBER(10) MODULE2                       2I have created a context which uses a procedure load_constants in a package global_constants, say . Right now this package is loading all the rows of CONSTANT_NAME and CONSTANT_VALUE using a logon trigger. I also have a get_val procedure in the package which returns the value of a constant when I query like following:
select global_constants.get_val('CONSTANT1') from dual;All is working fine till here. But, if you observe, the constant names are common in my table, but they are seggregated by SOURCE_ID. Now, my question is that, is there a way I can have the constant names common, but can retrieve the values based on the SOURCE_ID and CONSTANT_NAME combination?
Since DBMS_SESSION.SET_CONTEXT accepts only three parameters (i.e, It only allows us to populate a max 2D array values), I am unable to set the combination. I already can think of a way of handling it a crude way by appending the combination and loading it. But, in the current situation, it is not possible to do so. Also, please note that the logon trigger does neither know which source has created this session nor which source values it should populate, so is populating everything.
Any Ideas?

Answer 1

SQL> select * from my_constants;
CONSTANT_ID CONSTANT_O CONSTANT_N CONSTANT_V CONSTANT_T CONSTANT_MODULE       SOURCE_ID
      10252 CONSTANT1  CONSTANT1  5000       NUMBER(10) MODULE1                       1
      10253 CONSTANT2  CONSTANT2  5001       NUMBER(10) MODULE2                       1
      10254 CONSTANT1  CONSTANT1  6000       NUMBER(10) MODULE1                       2
      10255 CONSTANT2  CONSTANT2  6001       NUMBER(10) MODULE2                       2
SQL> CREATE OR REPLACE PACKAGE my_constant_info
  2  IS
  3     PROCEDURE load_context;
  4 
  5     FUNCTION get_val (in_constant_name IN VARCHAR2)
  6        RETURN VARCHAR2;
  7  END my_constant_info;
  8  /
Package created.
SQL> CREATE OR REPLACE PACKAGE BODY my_constant_info
  2  IS
  3     PROCEDURE load_context
  4     IS
  5        l_names    DBMS_SQL.varchar2s;
  6        l_values   DBMS_SQL.varchar2s;
  7 
  8        CURSOR con_cur
  9        IS
10           SELECT   constant_name, constant_value
11               FROM my_constants
12           ORDER BY constant_id DESC;
13 
14        l_count    NUMBER (8);
15        l_name     VARCHAR2 (100);
16        l_val      VARCHAR2 (400);
17     BEGIN
18        FOR i IN con_cur
19        LOOP
20           l_count               := con_cur%ROWCOUNT;
21           l_names (l_count)     := i.constant_name;
22           l_values (l_count)    := i.constant_value;
23           DBMS_SESSION.set_context ('my_context', l_names (l_count),
24                                     l_values (l_count));
25        END LOOP;
26     EXCEPTION
27        WHEN OTHERS
28        THEN
29           DBMS_OUTPUT.put_line (l_count || ', ' || l_name || ': ' || l_val);
30           RAISE;
31     END load_context;
32 
33   FUNCTION get_val (in_constant_name IN VARCHAR2)
34        RETURN VARCHAR2
35     AS
36        l_return_val   VARCHAR2 (400);
37        l_null_val     EXCEPTION;
38     BEGIN
39        l_return_val    := SYS_CONTEXT ('my_context', in_constant_name);
40 
41         IF l_return_val IS NULL
42        THEN
43           RAISE l_null_val;
44        ELSE
45           RETURN l_return_val;
46        END IF;
47     EXCEPTION
48        WHEN l_null_val
49        THEN
50           raise_application_error (-20011,
51                                       'Requested Constant '''
52                                    || in_constant_name
53                                    || ''' Returned Null.');
54     END get_val;
55  END my_constant_info;
56  /
Package body created.
SQL> CREATE CONTEXT my_context USING my_constant_info;
Context created.
SQL>
SQL> CREATE OR REPLACE TRIGGER my_constant_logon
  2     AFTER LOGON ON DATABASE
  3  BEGIN
  4     my_constant_info.load_context;
  5  EXCEPTION
  6     WHEN OTHERS
  7     THEN
  8        RAISE;
  9  END;
10  /
Trigger created.
SQL> BEGIN
  2     my_constant_info.load_context;
  3  END;
  4  /
PL/SQL procedure successfully completed.
SQL>
SQL> select my_constant_info.get_val('CONSTANT1') from dual;
MY_CONSTANT_INFO.GET_VAL('CONSTANT1')
5000
SQL> I am able to get the value 5000. But, if you look at the data back, there are two rows with CONSTANT1 one for source_id 1 and another for 2. The values of the CONSTANT1 changes according to the source_id. I would like to implement such a solution that it will have to output the values based on the combination of CONSTANT_NAME and SOURCE_ID
One way (not practical for me) is as follows:
SQL> CREATE OR REPLACE PACKAGE BODY my_constant_info
  2  IS
  3     PROCEDURE load_context
  4     IS
  5        l_names    DBMS_SQL.varchar2s;
  6        l_values   DBMS_SQL.varchar2s;
  7 
  8        CURSOR con_cur
  9        IS
10           SELECT   constant_name ||'-'|| source_id constant_name, constant_value
11               FROM my_constants
12           ORDER BY constant_id DESC;
13 
14        l_count    NUMBER (8);
15        l_name     VARCHAR2 (100);
16        l_val      VARCHAR2 (400);
17     BEGIN
18        FOR i IN con_cur
19        LOOP
20           l_count               := con_cur%ROWCOUNT;
21           l_names (l_count)     := i.constant_name;
22           l_values (l_count)    := i.constant_value;
23           DBMS_SESSION.set_context ('my_context', l_names (l_count),
24                                     l_values (l_count));
25        END LOOP;
26     EXCEPTION
27        WHEN OTHERS
28        THEN
29           DBMS_OUTPUT.put_line (l_count || ', ' || l_name || ': ' || l_val);
30           RAISE;
31     END load_context;
32 
33   FUNCTION get_val (in_constant_name IN VARCHAR2)
34        RETURN VARCHAR2
35     AS
36        l_return_val   VARCHAR2 (400);
37        l_null_val     EXCEPTION;
38     BEGIN
39        l_return_val    := SYS_CONTEXT ('my_context', in_constant_name);
40 
41         IF l_return_val IS NULL
42        THEN
43           RAISE l_null_val;
44        ELSE
45           RETURN l_return_val;
46        END IF;
47     EXCEPTION
48        WHEN l_null_val
49        THEN
50           raise_application_error (-20011,
51                                       'Requested Constant '''
52                                    || in_constant_name
53                                    || ''' Returned Null.');
54     END get_val;
55  END my_constant_info;
56  /
Package body created.
SQL> BEGIN
  2     my_constant_info.load_context;
  3  END;
  4  /
PL/SQL procedure successfully completed.
SQL> select my_constant_info.get_val('CONSTANT1-1') from dual;
MY_CONSTANT_INFO.GET_VAL('CONSTANT1-1')
5000
SQL> select my_constant_info.get_val('CONSTANT1-2') from dual;
MY_CONSTANT_INFO.GET_VAL('CONSTANT1-2')
6000
SQL> I would like to know any other elegant way of implementing the same, where in if I say something like
select my_constant_info.get_val('CONSTANT1', p_source_id) from dual;
or
v_cons_val := my_constant_info.get_val('CONSTANT1', p_source_id);
** where p_source_id is a value passed to a procedure and v_cons_val is a variable, say.Please let me know if you need any further infomation.