DB Access Exception Handling Policy

Overview

We do not yet have a consistent way of handling DB Access Exceptions in all situations. This is strongly desired.

TODO: Improve section on DB Access Exceptions in the Error and Exception Handling Policy.

Exception Handling

• Scenario 1: just reading data
  • Way 1: Commit before first Catch Clause + Commit in Catch Clause(s), no Finally Clause
    • Advantage:
      • No Finally Clause needed, therfore less deep nesting of code.
    • Disadvantage:
      • Commit can be accidently forgotten about by developers, leaving an open, 'dangling' DB Transaction - this is also true for the case where a 'return' statement is executed in the 'try' code block of the try-catch Clause!!!
  • Way 2: Commit in Finally Clause which encloses try-catch Clause
    • Advantage: Commit can never be forgotten about - this is also true for the case where a 'return' statement is executed in the 'try' code block of the try-catch-finally Clause!!!
    • Disadvantage: Finally Clause is needed, therfore deeper nesting of code.

Recommendation (ChristianK): We should discourage 'Way 1' and ensure that 'Way 2' is implemented everywhere.

• Scenario 2: Writing Data / mixed reading/writing of data
  • Way 1: Commit before first Catch Clause + Rollback in Catch Clause(s), no Finally Clause
    • Advantages:
      • No Finally Clause needed, therfore less deep nesting of code.
      • No bool Variable needed (see below).
    • Disadvantages:
      • Developers must not forget to do a Rollback in ANY Catch Branch!
      • Commit can be accidently forgotten about by developers, leaving an open, 'dangling' DB Transaction.
  • Way 2: Commit or Rollback in Finally Clause which encloses try-catch Clause, depending on value of bool Variable ('SubmissionOK'). DB Transaction is not committed before first Catch Clause and not Committed / Rolled Back in any Catch Clauses. (Example: C:\openpetraorg\trunk\csharp\ICT\Petra\Server\lib\MSysMan\UserDefaults.cs, line 964)
    • Advantage: Commit or Rollback can never be forgotten about - this is also true for the case where a 'return' statement is executed in the 'try' code block of the try-catch-finally Clause!!!
    • Disadvantages:
      • Finally Clause is needed, therfore deeper nesting of code.
      • bool Variable needed.

Recommendation (ChristianK): We should discourage 'Way 1' and ensure that 'Way 2' is implemented everywhere.

DB Transaction Handling

• handling of long running DB Transaction over many Method Calls ('Control Method' / 'Super Structure')
  • Discussion: http://sourceforge.net/apps/phpbb/openpetraorg/viewtopic.php?p=364#p364
    • Starting of a local DB Transaction or use of a Session Object?
    • Exception handling