Dynamic Typed Table/Model in Java EE?

Question

Usually with Java EE when we create Model, we define the fields and types of fields through XML or annotation before compilation time. Is there a way to change those in runtime? Or better, is it possible to create a new Model based on the user's input during the runtime? Such that the number of columns and types of fields are dynamic (determined at runtime)?

Help is much appreciated. Thank you.

I felt the need to clarify myself.

1. Yes, I meant database modeling, when talking about Model.

2. As for the use cases, I want to provide a means for users to define and create their own tables. Infinite flexibility is not required. However some degree of freedom has to be there: e.g. the users can define what fields are needed to describe their product.

Answer 1

You sound like you want to be able to change both objects and schema according to user input at runtime. This sounds like a chaotic recipe for disaster to me. I've never seen it done.

I have seen general schemas that incorporate foreign key relationships to generic tables of name/value pairs, but these tend to become infinitely flexible abstractions that can neither be easily understood nor get out of their own way when it comes to performance.

I'm betting that your users really don't want infinite flexibility. I'd caution you against taking this direction. Better to get your real use cases straight.

Anything is possible, of course. My direct experience tells me that it's a bad idea that your users will hate if you can pull it off. Best of luck.