Hello everyone,

As the subject says, I'm in the process of creating such a beast. As such, I have two session factories, unlike what is usually recommended, but it's a necessity here.

The first one is dedicated to accessing, and modifying, the object definitions (a POJO mapped to a simple two columns table, one with the entity name, the other with the contents of the Hibernate mapping file). I then use the stored definitions to rebuild the second session factory.

This second session factory is therefore dynamically updated. I spawn sessions with either dynamic-map mode or dom4j mode. The user never sees Hibernate sessions directly, instead I spawn an object from which it can do its stuff (getting the object list, getting an object template to fill, listing objects, writing objects). The object is created with its creation date as a field, and as such I can detect whether the configuration (and therefore the session factory) has been updated in the meanwhile, and proceed only if the template it uses is valid (object exists, its editable fields haven't changed, etc). This is what I use to rebuild the configuration (wlock is the writeLock() or a ReentrantReadWriteLock, persistor has all mappings "pre-digested"):



I can add and remove mappings, and when I regenerate the session factory, Hibernate updates the tables for me, so far so good. But it doesn't delete tables, however. Is there a way to get the DDL from Hibernate to delete a table?

Also, I haven't played yet with "multiple column fields" or even foreign keys. Here is how I detect what fields can be edited, what fields are compulsory. So far, it works, but is there a better way?



Thanks,

Reply to self...

Hibernate's hbm2ddl is not stateful, since SessionFactories are not, so I used a workaround:



And it works :)

But I have learned about the more general SchemaUpdate object, which can ease the process further.

Looks like an interesting project, Hibernate lacks dynamic mapping behaviour.

This is especially bad for modularized applications since you need to build a huge SessionFactory at application start (with all of the classes of the application) instead of being able to add classes only when they are actually needed.

Keep us posted, I would be very happy to use a Hibernate-variant which is capable of dynamically accepting new persistent classes in a SessionFactory !!!

Hello, and thanks for your interest ;)

I have to say, though, that I don't use POJOs, I use the dynamic-map and dom4j entity modes only. Using classes would require a class generator which I just don't know how to program at all (Hibernate does this, I know, but I don't know either where or how - I'm just not ready to dive into that code, since POJO is not my priority).

Apart from the POJO side, I'm making progress. The core is coded and tested, but lacks some fundamental stuff due to Hibernate's lack of DDL capabilities (Hibernate cannot add an index to an existing column, for one; I have spotted other limitations, too, which I'm working on fixing). I also have an HQL query generator from XML which works but is far from being complete.

When I get to a fully functional prototype, I'll publish it, but it WILL require patches to Hibernate itself, I just cannot achieve what I really want without modifying Hibernate's Dialect...

Hibernate's SchemaUpdate and SchemaExport have a LOT of limitations, I don't recommend using them. They are suggested for development only anyway, not for production databases.

We use Liquibase XML changesets for DDL management, which is a nice, database-independent schema transformation management tool.
We write the schema creation and schema update scripts manually for absolute control.

You may generate the changesets according to your dynamic model and execute them with an embedded Liquibase instance.

good work fge,
Looks very interesting, In fact we can use something like this in our project right now. Do you know how soon you would be have this available? Integrated liquibase would be cool for DDL.

-Shailesh