Question

I am working with brownfield database that uses strings as primary keys.
Using Fluent NHibernate with Sqlite (in-memory provider for unit testing) and SQL Server 2005.

I have the following entity:

public class Entity
{
    public virtual DateTime TimeStamp { get; set; }

    public virtual string Name { get; set; }
}

With this mapping:

public class EntityMap : ClassMap<Entity>
{
    public EntityMap()
    {
        Map(_ => _.TimeStamp);
        Id(_ => _.Name).CustomType("AnsiString");
    }
}

However it does not work saying NHibernate.TypeMismatchException : Provided id of the wrong type. Expected: System.Int32, got System.String

How make this work? Also, is there any good documentation about fluent nhibernate available?

Thanks in advance.

Answer 1

If you are using strings as your primary keys you’ll probably have to do something like this:

public class EntityMap : ClassMap<Entity>
{
    public EntityMap()
    {
        Id(x => x.Name).GeneratedBy.Assigned();
        Map(x => x.TimeStamp);
    }
}

From the nhibernate documentation:

5.1.4.7. Assigned Identifiers

If you want the application to assign identifiers (as opposed to
having NHibernate generate them), you may use the assigned generator.
This special generator will use the identifier value already assigned
to the object’s identifier property. Be very careful when using this
feature to assign keys with business meaning (almost always a terrible
design decision).

Due to its inherent nature, entities that use this generator cannot be
saved via the ISession’s SaveOrUpdate() method. Instead you have to
explicitly specify to NHibernate if the object should be saved or
updated by calling either the Save() or Update() method of the
ISession.

Also here is a related article. It is a bit dated but still applies to your situation:

http://groups.google.com/group/fluent-nhibernate/browse_thread/thread/6c9620b7c5bb7ca8