Apple

On Jun 18, 2012, at 5:31 PM, Ramsey Gurley <email@hidden> wrote:

Speaking of which, I wonder what migrations do for cross db fks? Does it blow up trying to form a constraint? I'll have to look sometime.

Which raises another interesting issue. Do you create cross model relationships Larry? I could see that causing problems. For example, create an EO in common with an FK to an EO in emr. Then change connections! Now the common EO's relationship points off into space, or worse, at some other object.

Maybe that could be mitigated by forming to-one's using a two key join table in the destination entity's DB with a unique index on one key column? Interesting problem in any case.

Ramsey

On Jun 18, 2012, at 2:04 PM, Larry Mills-Gahl wrote:

Not automatically. Migrations happen during the application startup and at that point, they have default connection dictionary information. I do use migrations but that just migrates the common databases and an empty stub database (that uses the default connection dictionary) on the main db server. Using that empty stub means that I don't have to worry about loading and unloading different model groups. If you aren't connected to a particular facility db, you are connected to the stub and EO is happy about all the objects, you just don't have any data.

I have some old perl that will iterate through the active databases to check schema consistency.

When I have extra time (come on ... stop laughing!!) finishing the utility to trigger migrations across active databases is on the list of things to do. Right now it's not an urgent or consistent issue so it doesn't get top priority.I haven't made this completely automatic (because I'm chicken and have an allergy to injecting lead into my own foot)

Larry Mills-Gahl
email@hidden

On Jun 18, 2012, at 4:47 PM, Chuck Hill wrote:

IIRC, it is not handled.

On 2012-06-18, at 1:43 PM, Ramsey Gurley wrote:

Out of curiosity, do you happen to know if it's possible to run migrations against multiple data stores like you have Larry?

Ramsey

On Jun 18, 2012, at 1:25 PM, Larry Mills-Gahl wrote:

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@hidden

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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Chuck Hill             Senior Consultant / VP Development

Practical WebObjects - for developers who want to increase their overall knowledge of WebObjects or who are trying to solve specific problems.
http://www.global-village.net/gvc/practical_webobjects

References:
	>Different Database Connection per session for the same model (From: Paul Dunkler <email@hidden>)
	>Re: Different Database Connection per session for the same model (From: Larry Mills-Gahl <email@hidden>)
	>Re: Different Database Connection per session for the same model (From: Ramsey Gurley <email@hidden>)
	>Re: Different Database Connection per session for the same model (From: Chuck Hill <email@hidden>)
	>Re: Different Database Connection per session for the same model (From: Larry Mills-Gahl <email@hidden>)
	>Re: Different Database Connection per session for the same model (From: Ramsey Gurley <email@hidden>)
	>Re: Different Database Connection per session for the same model (From: Mike Gargano <email@hidden>)