Re: [Modeling-users] leaving the database open

[Sebastien B. <sbi...@us...>]

  Hi and sorry for the delay in the answer,

"Ernesto Revilla" <er...@si...> wrote:
> Hi all,
>=20
> strange thing (for me) that the AdaptorContext does not define a close
> operation.
>=20
> Working with SQLite, I only see code to close the database when all chann=
els
> are closed and the os.environ.get('MDL_TRANSIENT_DB_CONNECTION') is set (=
to
> something different as '' and 0).

You're right: the connection to the db is only closed in this situation.
So, if you need to close it after an operation, you have to set
MDL_TRANSIENT_DB_CONNECTION to true before that operation.

  The mechanism will probably change however in the near future; maybe a
  delegate can handle those situations.

  Now if you need a method to close the database connection after some
operations took place, this can be made the way it is in
AbstractDBAPI2AdaptorContext.adaptorChannelDidClose() -- the important
thing is to set self._cnx to None so that it automatically reconnects
when needed. If you're doing this in a multi-thread environment with
many ECs, you should lock the ObjectStoreCoordinator (which is any EC's
rootObjectStore()) before closing the connection.


> The problem arose when I executed the mdl_create_DB_schema.py with
> execfile from within my PyModel definition with execfile with the -R
> option. The database was open (after running a schema creation). So
> rerunning the script with some changes in the model, didn't drop the
> DB.
>=20
> So I have the following questions:
> * does loading the model open the database?

Not at all --if you want to see when the db connection is opened you can
MDL_ENABLE_DATABASE_LOGGING to "yes".

> * is it possible to close explicitly the database, i.e. context, so
> that after the creation of the schema the database is closed?

I'll suggest setting MDL_TRANSIENT_DB_CONNECTION

> * what does the MDL_TRANSIENT_DB_CONNECTION mean:
>   a) do not close the DB when all cursor have closed, or
>   b) the opposite, close the DB when all channels are closed?

If set to true, it closes the db when the last opened channel is
closed. The default behaviour is now to keep the db connection
opened. BTW I've just realized that the User's Guide says exactly the
opposite, this should be fixed.

>=20
> If mdl_generate_DB_schema.py is invoked with the -R option, using
> SQLiteAptor, and the file does not exist, an error is rosen. Perhaps this
> could be ignored. (-R is: drop the database if it exists). This could be
> done with the following code in
> dropDatabaseWithAdministrativeConnectionDictionary:
>=20
>     try:
>       os.unlink(administrativeConnectionDictionary['database'])
>     except OSError, exc:
>       # ignore if file does not exist, else, reraise exception
>       if not exc.errno=3D=3D2:
>         raise


Well, the error shouldn't be ignored when the file does not exist to be
consistent with other adaptors which also raise when an attempt is made
to drop an non-existing database.

In the script, -R is: drop the db and recreate it and agreed, it fails
if the database does not exist; if you want to ignore the error, the
option -i/--ignore-errors is your friend :)  Now if you want to
explictly ask for DB creation (not re-creation), then you want to use
-C.

  I'm not sure I fully understood your use-case with executing the
  script, hopefully this answers your question.

-- S=E9bastien.