Using multiple databases in a Spring JPA application

Question

I have a Spring application which supports a single customer.

I would like to extend this application to support multiple customers where each customers database is stored in a separate database. The schema for the database is the same for each customer, and the same DAOs and business logic should remain the same.

How would I accomplish this with Spring/JPA? Would I need to have multiple persistence contexts and wire in an appropriate entity manager factory based upon the currently logged in user? Are there any examples of implementing something similar to this?

beny23 · Accepted Answer · 2011-08-19 10:50:25Z

I would advice against running separate database under a single application. If a redesign of the data model to incorporate multiple customers is not an option, why don't you run multiple instances of your application server/web container, one for each customer? As otherwise you'll have to deal with the drawbacks of having a shared platform and isolated databases.

With multiple customer databases and a single application your code will become more complex, you can't guarantee that customer data is fully isolated (e.g. due to a bug in the application a customer is shown the wrong data, so there's not much benefit in isolating each customer) and you'll have the nightmare of maintaining each customer database. Also, by having different databases you can virtually guarantee that someone pointy-haired is going to ask for some bespoke functionality for customer A while leaving customer B's functionality untouched, because "... it will be easy, as we've got different databases...", forgetting that the application is shared.

MaDa · Accepted Answer · 2011-08-19 10:37:16Z

If you really, really want to have separate databases for particular customers, this would be the way to go — define separate persistence units with the same entity definitions, but different entity manager factory configurations.

To me it sounds more like a need to redesign the database structure. I'm guessing that the application has been written for only one client in mind and it turned out that more appeared on the horizon, so, hey, let's do something about it, and fast! Aren't you trying to copy-paste, but in a bigger scale? You'll going to have a lot of redundancy with JPA if you want to have a few databases with the same structure: for example, everything what's defined inside the mapping-file (queries, entity relationship mappings, etc.) is defined per persistence unit — you'll have to repeat these definitions and keep them all synchronized.

I'll stop here, as it is merely guesswork, for the lack of broader description.

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