Using Hibernate for Existing Database

Question

We have an application thats already running for a long time. Now we are migrating it to Spring and possibly using Hibernate or any other ORM.

But we caught up with a question. Is it not recommended / bad idea to use Hibernate for the already existing Database and model the object around Schema?

Most people advocate NOT using Hibernate and instead of go with some other ORMs like iBatis. But in our company, all are proponents of Hibernate.

Any experiences?

Answer 1

Hibernate works well if you can model your database under your objects.
Vice versa, you are likely to get the database model as your your domain model. You need to evaluate how distant those two models are, otherwise you are going to map the database => ORM objects => your domain model. I would avoid that.

If I want to skip the ORM part, I find myself quite happy with JDBI which I prefer over Spring JDBC Template

Answer 2

I would say that it's irresponsible to choose Hibernate, iBatis, or anything else without knowing your requirements.

If you don't have a solid object model, I'd say that Hibernate is a terrible choice.

If you use stored procedures as the interface to your database, I'd say that Hibernate is a terrible choice.

If you don't like the dynamic SQL that Hibernate generates for you, I'd say that Hibernate is a terrible choice.

Get it? Knee-jerk reactions like the ones from those Hibernate proponents aren't a good idea.

It might be that iBatis or Spring JDBC template is a better choice than Hibernate. You ought to become more informed about that decision and make it for your application rather than blindly listen to a mob.

You don't have to be all or none about it, either. It's possible to implement part of your solution with one technology and the rest in another.

I'd recommend making your persistence layer interface-based so you can swap implementations without affecting clients.

Answer 3

I recommend looking at SansORM (a NoORM object mapper). It is designed for SQL-first development, which fits well with retrofitting an existing schema.

Answer 4

As others have pointed out an ORM is only a good choice if your database is not far from an object model.

If that is the case then an option would be Hibernate through JPA for two resons:

• Netbeans has a tool to generate JPA Entities from an existing database. This entities are not dependant on Netbeans so you could use a different IDE after the initial reverse engineering.

• Spring Data JPA can avoid writing trivial queries and focus on the hard ones.