Revision as of 16:35, 31 May 2011

Parsing DDL for Metadata

The primary job of the DBWSBuilder utility is to extract metadata from the database about some artifact (i.e. a Table or a StoredProcedure) that is to be used as the basis of a (JAX-WS compliant) Web Service. The DBWSBuilder translates the information (fields, arguments, scalar or complex datatypes, etc.) into DBWS runtime artifacts (e.g. EclipseLink Project XML files, JAX-WS Provider class, etc.) Thus it is crucial that DBWSBuilder get complete and accurate metadata from the database.

For Oracle databases, DBWSBuilder uses a modified cut-down version of the JPublisher classes to send SQL queries to Data Dictionary views (ALL_OBJECTS, ALL_ARGUMENTS, etc.) that is then converted to an in-memory object-graph of all relevant information about the specific database artifact required for the Web Service. This object-graph is then walked and the required DBWS runtime artifacts generated.

Unfortunately, the information in the Data Dictionary views can be (under certain circumstances) incomplete or inaccurate, or the in-memory object-graph constructed from the views can be distorted. For example, an argument to a StoredProcedure may have a default value assigned to it, thus making it optional. This in turn means that the calling sequence can change in that fewer arguments need be passed in:

CREATE OR REPLACE PACKAGE SOMEPKG AS
 
  TYPE EMP_REC IS RECORD(
    EMPNO EMP.EMPNO%TYPE,
    FNAME EMP.FNAME%TYPE,
    LNAME EMP.LNAME%TYPE
  );
 
  PROCEDURE DOSOMETHING(MYREC IN OUT EMP_REC, STUFF IN VARCHAR2,
    P_EMPNO IN NUMBER := 20, FLAG IN BOOLEAN DEFAULT FALSE,
    WHATEVER IN VARCHAR2 DEFAULT 'bogus');
END;

The object-graph created 4 StoredProcedure representations:

DOSOMETHING(MYREC,STUFF)
DOSOMETHING(MYREC,STUFF, P_EMPNO)
DOSOMETHING(MYREC,STUFF, P_EMPNO, FLAG)
DOSOMETHING(MYREC,STUFF, P_EMPNO, FLAG, WHATEVER)

however, there are an additional 4 possibilities:

DOSOMETHING(MYREC,STUFF, FLAG)
DOSOMETHING(MYREC,STUFF, WHATEVER)
DOSOMETHING(MYREC,STUFF, FLAG, WHATEVER)
DOSOMETHING(MYREC,STUFF, P_EMPNO, WHATEVER)

This also highlights a problem where the number of in-memory objects could expand geometrically 2^N