Best way to connect to multiple databases with same schema?

[Eric Hermanson]

I have a situation where I need to connect to several different
databases (via ODBC), all of which have the same schema. Rather than
duplicating the same model 'X' number of times (with different
connection dictionaries), I'm wondering if there is a better way to go
about it?

In this situation, the entity, rather than the model, would need to know
about several different databases (and their connection dictionaries).
I'm just unsure of exactly what "level" within EOF I should be
manipulating to perform such a query (i.e. maybe create several
adaptor/database channels, modify EOEntity/EOAdaptor, take advantage of
certain delegate methods, etc)?

Here are some requirements of the data fetch:

- read-only (no update/insert/delete of data required)

- fetch all data from all tables into the same entity such that I
get one result array when calling [editingContext
objectsWithFetchSpecification:xxx]

- allow for a timeout on each database so if no data is available,
it will skip that database and go to next, possibly sending a
notification alerting that the given database is down.

- i would like to incorporate this information into a WebObjects 3.1
application which will offers the possibility of running queries in the
background and returning data to the user as it becomes available. I've
heard that WO4.0 has some support for this type of thing, but I'm
wondering if it's possible with 3.1?


Thank You,
Eric

[Philippe Converset]

Post by Eric Hermanson
I have a situation where I need to connect to several different
databases (via ODBC), all of which have the same schema. Rather than
duplicating the same model 'X' number of times (with different
connection dictionaries), I'm wondering if there is a better way to go
about it?

Yes, you can use the same model on different databases. All you have to do
is set the right connection dictionary on the model.

In the ODBC case, you have to create a Data Source via "ODBC Data Source
Administrator", it is not necessary to choose a database in your Data source
since it will be affected by code.
You must create, in your code, a connection dictionary for each database.
Each connection dictionary must have its DBQ part in the connectionString
key properly affected to the path of the database (ex. :
DBQ=C:\Production1\Episod27\Databases\db.mdb).
You must use of course a different editing context for each database, these
contexts are created like this :
EOObjectStoreCoordinator *coord = [[[EOObjectStoreCoordinator alloc] init]
autorelease];
editingContext_ = [[EOEditingContext alloc]
initWithParentObjectStore:coord];

Before every fetch on an editing context, set the right connection
dictionary on your model (method -[A2Model setConnectionDictionary:]). This
should work well.

Phil.