Question

Using the latest version of NHibernate (and possibly some plugins), is that possible to map entities across multiple databases on different servers without DB link?

For the background, I’m looking to implement something loosely similar to what is described in this DBA.SE post.

Answer 1

I’ve got an interesting answer on the nhusers mailing list. Excerpt follows:

From Jason Meckley

[…] if you are talking about storing
a single entity across multiple
databases, the answer is not cleanly.
you might be able to do something with
custom user types and/or event
listeners to hydrate the object, but
that would be a mess to maintain.

A different approach is to transfer
the data from one db to another using
an ETL process. similar to
replication, but only transferring the
data required by the other database.
you end up with 1 writable database
and many read databases. then you map
the domain to a single database.

Another option is to determine why
there are multiple databases. if they
represent different types of
data/objects then explicitly express
this in the domain. for example
CustomerWithAddress is a different
entity than CustomerOrder. If you need
information from both, then query each
database individually and build up a
projection in code.

var x =
session1.get(id);
var y =
session2.get(id);
return merge(x, y);