SYS_CONTEXT

Question

Can any one explain me what below code do how i can check context values.
c_working_airport_predicate CONSTANT VARCHAR2 (500)
:= ' SYS_CONTEXT ('''
|| c_session_context
|| ''','''
|| c_airport
|| ''') IN '
|| '(pri_working_airport_code ,'
|| ' sec_working_airport_code)';
Thanks,

Answer 1

Seems like some kind of dynamic security predicate that is applied at run-time.
A context is a namespace in a session, containing name-value pairs. E.g. I can create a namespace called EMPDATA. As part of the logon processing of the session, this context gets a name-value pair called ROLE, indicating the session user's role as per HR data. The name-value pair could for example be ROLE=SUPERVISOR.
To view the value from this namespace for the attribute, role:
SYS_CONTEXT( 'EMPDATA', 'ROLE' )
Name values are typically compared with other values (from a table for example) at runtime - in order to make a query succeed or fail, or limit the data output of that query. For example, the above sys context function can be used to limit a query's output to rows only a user with supervisor access can see,
select * from some_table where col123 = SYS_CONTEXT( 'EMPDATA', 'ROLE' )
And that is what the code snippet you post does - dynamically. It gets the value from a namespace (value is in <i>c_session_context</i>) for attribute identified by c_airport. it then uses it in a predicate.
What is unusual is that the context's name is variable, and that the attribute name is also variable. This points to a possible flawed implementation/solution.