Mapping custom GUID with Fluent NHibernate

Using Guids "normally" In your entity the Id should be of type Guid:

public virtual Guid Id { get; private set; } 

And in your ClassMap you should map it like this:

Id(x => x.Id) .Column("Id") .GeneratedBy.GuidComb();

This will use the recommended comb algorithm to generate new guids.

or

Id(x => x.Id) .Column("Id") .GeneratedBy.Guid();

to genertae new Guids using System.Guid or

Id(x => x.Id) .Column("Id") .GeneratedBy.GuidNative();

if you want to let the database generate the Guid for you.

EDIT: CompositeId does not have the GeneratedBy method as I thought, the source of the issue may be the mapping for the KeyReference method. Check the Well class mapping to ensure it is set to assigned since no native identity (Oracle sequence in your case) is valid for that id.

You need to tell NHibernate you are assigning the Id manually for that entity. Try something like the mapping shown below. Of course, when you create new instance of this entity you will need to set the appropriate values for GUID & SetDate in your code. You will also need to assign the appropriate Well class instance to the Well property.

CompositeId() .KeyReference(x => x.Well, "WellID") .KeyProperty(x => x.GUID, "GUID") .KeyProperty(x => x.SetDate, "SET_DATE") .GeneratedBy.Assigned();