For a long time I have been meaning to add somesort of data abstraction layer to the NeuClear Ledger which is the core book entry library used in NeuClear Pay.

What I wanted from this primarily is to:

• Maintain and Create a Schema
• Abstract away from the physical database
• minimal configuration ( I hate XML as a configuration method)

I liked the looks of Hibernate and OfBiz’s Entity Engine, but everytime I wanted to start integrate one of them, it became a nightmare of dependencies and unwanted xml configuration files.

So I came to the conclusion that I dont mind writing sql, for my purposes it’s actually quite simple. So I simply want something now where I can maintain my schema with a minimum of fuss.

Which is why I have now added my own lightweight Entity Engine. It is currently in CVS as part of NeuClear Commons

My idea is to generate Entities using a simple programatic interface that suits my purposes.

The following is an example schema:

EntityModel ledgerModel=new EntityModel("ledger",true);
ledgerModel.addTitle();
ledgerModel.addTimeStamp();

EntityModel bookModel=new EntityModel("book",true);
bookModel.addTitle();
bookModel.addTimeStamp();

EntityModel xactModel=new EntityModel("transaction",true);
xactModel.addComment();
xactModel.addValueTime();
xactModel.addReference(ledgerModel);

EntityModel entryModel=new EntityModel("entry",false);
entryModel.addMoney();
entryModel.addReference(bookModel);
entryModel.addReference(xactModel);
entryModel.create(connection);

To create a table I simply instantiate a new EntityModel. The boolean field in the constructor allows me to pick one of two general primary key models that I use A large number or String URI. This model now contains the primary key and nothing more. I then simply add columns using the addXXX methods.

Several of these column methods define standard column names as well, such as id, comment, amount etc., to alleviate boring repetition.

Table relations are added by the addReference(org.neuclear.commons.sql.entities.EntityModel) method, which takes another EntityModel as a parameter.

Finally I just call the create(java.sql.Connection) method on one of the EntityModel’s which generates the table and any dependencies on the given JDBC Connection.

So the current status is development and unstable. I have the beginnings of an insert row method, which takes an object array. But to be honest, I dont see much point in that at the moment. I will do all inserts and selects manually for now.