How to map to abstract base class?

markalroberts · **Joined:** Thu May 31, 2007 1:19 pm **Posts:** 23

Hi,

A set of classes that inherit from an abstract base class that has a set of common properties. Each concrete class has it's own table in the DB.

abstract class AC{
public string Id,
public string Name,
public string Description
}

class C1 : AC{
public int Credit
}

class C2 : AC{
public int Age
}

In my mapping XML, I would like not to have to define the Id, Name and Description _for each_ <class> elment (i.e. I wish to have a similar notion of inherited values in the XML definition).

Is this possible?

Thanks,
Mark.

marcal · **Posted:** Mon Jul 16, 2007 2:09 pm

I don't think so.

harald_m_mueller · **Joined:** Wed Nov 29, 2006 10:32 am **Posts:** 34

[... oops - I misread your posting ...]
No, I also think it's impossible. Maybe the attributes in the the contributions can do this - but I did not look ...
(We use our own code generator to create the XMLs, and there, you can do such things easily).
Regards
Harald

markalroberts · **Joined:** Thu May 31, 2007 1:19 pm **Posts:** 23

Hi,

One can do something like this:

[Class(NameType(Class1))]
Class1: BaseClass{
}
[Class(NameType(Class1Ext))]
Class1Ext: BaseClass{
[Property]
}
BaseClass{
[Id, Generator]
[Property]
[Property]
}

As long as there is no "Class" attribute for the base class, the attributes are inherited together with the properties of the class (actually if you can examine the XML configuration created by the HbmSerializer, and it expands the super classes out, copying the attributes from the base)

mnichols · **Joined:** Mon Aug 21, 2006 9:18 am **Posts:** 179

You may want to check out my blog posting on this at
http://blogs.chayachronicles.com/sonofnun/archive/2007/06/26/251.aspx

You CAN do what you are after.

Hope this helps,
Mike

markalroberts · **Joined:** Thu May 31, 2007 1:19 pm **Posts:** 23

I looked at this in my travels... I think the problem is with these subclasses is that one needs a descriminator column - i.e. if I understand it, a column that tells NHibernate which subclass to instantiate in a table-per-class hierarchy scenario.

Now, this is not something I have in my schema :(

Mark.

mnichols · **Joined:** Mon Aug 21, 2006 9:18 am **Posts:** 179

Yes a discriminator column is required for the table-per-class-hierarchy strategy and if you have no control over your db schema then that wouldn't work.
However, if you ARE actually able to modify db schema and are holding to a predefined schema based on your relational view of the domain, then I'd encourage you to consider putting the discriminator in. Domain design should determine the table schema, not vice versa.

Good luck!
Mike