[odb-users] Get real error reason from object_already_persistent

[Boris Kolpackov]

Hi Mikhail,

Tomilov.Mikhail <Mikhail.Tomilov at infotecs.ru> writes:

> I need to insert a row into users table, which has unique constraint
> on "login" field and some FK. If I insert row with duplicate login
> field I get object_already_persistent exception. AFAIK
> object_already_persistent exception is thrown when any postgresql
> constraint fails. It could be PK constraint, unique constraint, FK
> constraint. Can I determine real reason for my case to pass correct
> error code to client?
> 
> It would be natural to get database error info from
> odb::object_already_persistent exception.

The issue is described in Section 19.5.3, "Unique Constraint Violations"
in the ODB manual:

"Due to the granularity of the PostgreSQL error codes, it is impossible
to distinguish between the duplicate primary key and other unique
constraint violations. As a result, when making an object persistent,
the PostgreSQL ODB runtime will translate all unique constraint violation
errors to the object_already_persistent exception."

There is also an informative thread that goes into more details and
discusses possible solutions:

http://www.codesynthesis.com/pipermail/odb-users/2012-September/000785.html

On the second thought, the _pkey suffix idea doesn't sound bad. It
is rarely that anyone assigns an explicit constraint name to the
primary key. 

Would you be willing to test the fix?

Boris