FluentMapping ComposedId with AutoInc

Question

I am creating a transfer data tool for the company application, to move data from the old version to the new, and back. Since now we are using NHibernate and FluentMapping, I'll have to map all old tables, and there is a problem with one table with composed primary key. The table looks like this:

public class OldTable {
 public string KeyOne {get;set}
 public string KeyTwo {get;set}
 public string KeyN {get;set}
 public int Sequence {get;set}
 ...
}

And I need to map all the above fields as a composite key, the only problem is that "Sequence" increments based on the other fields to avoid duplicated keys, the others are a mix of foreign keys and simple strings. Is there a way to do this mapping? If it takes creating a expression to calculate the Sequence, no problem.

The good news is the table in the new system just uses a integer Id.

Daniel Schilling · Accepted Answer · 2013-11-01T19:21:43.487

From the documentation:

You can't use an IIdentifierGenerator to generate composite keys. Instead the application must assign its own identifiers.

You see this in the HBM XML schema, too. <id> allows a <generator> to be specified, but <composite-id> does not.

That's not to say this feature couldn't be added to NHibernate. If this is something that would be useful to you, please submit your feature request to the NHibernate issue tracker. Your feature request is most likely to be successful if this feature has been implemented in Hibernate first - if so, it may be simple to port it over. It sounds like it may be implemented in Hibernate already: HHH-2060

score -2 · Answer 2 · answered May 29 '12 at 15:46

Yep, trying to create NHibernate mappings for a legacy database is a total pain. Composite keys are a particular area of fun.

When you say you need to map all fields as primary keys I'll assume that you mean a composite key as you can only have a maximum of one primary key in a table. In that case, would something like the following in your mapping class not work?

CompositeId()
    .KeyProperty(x => x.KeyOne).KeyProperty(x => x.KeyTwo)
    .KeyProperty(x => x.KeyN).KeyProperty(x => x.Sequence)

If you're just trying to read the data out of the legacy database you may have some luck but if it was me, in this scenario I'd probably avoid trying to map NHibernate onto the old legacy database and just write the data mapping code by hand. In my experience it would probably be quicker, easier and less painful.

Actually I mean all fields in the example represents a composite single primary key, the problem is the Sequence (last field in the composite), how to map so it increments correctly? And yes, it is a two way tool. — maiconmm, May 29 '12 at 16:58
-ve vote since the actual problem is not solved as mentioned in the comment above — keyr, Oct 30 '13 at 05:18

FluentMapping ComposedId with AutoInc

2 Answers2