I do have an app with a different database connection per session. This does
appear to be relatively uncharted territory, but it has been working in
production for a while and it has been working pretty well. This is not a high
volume transactional application.
I use two models in this setup. One is a common or application wide model and
the other contains the data specific to the logged in user. The common model
contains the information necessary to connect to databases based on state in
the session. In my case, the database connection may change based on the
authorizations of the logged in user (admins can change db connections for
various purposes and it is possible for a user to be authorized to view data in
a number of databases... rare, but possible)
I don't know if there is a better way to do this, but this is the way I have
come up to achieve this end. The key (as others here have mentioned) is to be
very careful about how you use editing contexts. I explicitly create the Object
Store Coordinators for the session and then use those to manage session
specific database connections.
Create the Object Store coordinator in the Session() constructor
emrOSC = new EOObjectStoreCoordinator();
emrEC = ERXEC.newEditingContext(emrOSC);
When someone changes their current facility, I check authorization then check
to see if I need to change the database and if I do, I dump the old OSC,
recreate it and connect:
ERXEOAccessUtilities.closeDatabaseConnections(emrOSC);
emrOSC.dispose();
emrOSC = new EOObjectStoreCoordinator();
emrEC = ERXEC.newEditingContext(emrOSC);
EOUtilities.connectWithModelNamed(emrEC, COMMON_MODEL_NAME,
null);
EOUtilities.connectWithModelNamed(emrEC, EMR_MODEL_NAME, cdict);
emrEC.setFetchTimestamp(System.currentTimeMillis());
Notice, I only want to override the database connection for the EMR Model so
all the others are reconnecting to the same (common) database. (By the way,
thanks to whoever wrote ERXEOAccessUtilities.closeDatabaseConnections because
it saves an awful lot of legwork iterating through channels and contexts and
such)
I'm pretty sure that I'm missing an awful lot of optimization that you get when
you take advantage of the way EO generally uses object store coordinators,
cooperating object stores and snapshots, but so far, that hasn't been a
problem. I tend to be a bit harsh in invalidating objects so that I don't get
into trouble with parts of the object graph that may be hanging around due to
my own carelessness so I'm moderately confident that if more optimization
becomes necessary, I can take advantage of more of the EOF goodness.
One good thing is that doing this really forces you do follow the editing
context best practices that have been talked about here and on the wiki (don't
use default ec, using localInstanceOf, use ERXEC...)
I'm always looking for better, more elegant ways to do this so any ideas or
patterns or suggestions are welcome.
Larry Mills-Gahl
[email protected]
On Jun 18, 2012, at 12:32 PM, Paul Dunkler wrote:
> Hi List,
>
> is there any way to have different database connections per session? I need
> this in an application for giving the user the ability to change between
> several different copies of the database to work on.
>
> I always tried to copy EOModels and so on, read some mails from the list but
> not really found an answer for that problem. I know that what i trying to do
> will cause a bit memory overhead but i do not want to provide ~25
> applications just because they need different database connections.
>
> Would be nice to get some suggestions...
>
> --
> With best regards
> Paul Dunkler
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