Fluent NHibernate subclass reference

Question

So I have following entities:

TimelineRecord:
    ID: PK
    From: DateTime
    To: DateTime

ServiceRecord extends TimelineRecord:
    ID: PK
    TimelineRecord_ID: FK
    SomeSpecificProperties...

Demand:
    ID: PK
    From: DateTime
    To: DateTime
    ...

ServiceDemandConnection:
    ID: PK
    Service: ServiceRecord
    Demand: Demand

TimelineRecord, Demand and ServiceDemandConnection are mapped using ClassMap with Id(x => x.Id). ServiceRecord is mapped using SubclassMap (table-per-class). References in ServiceDemandConnection are mapped using References(x => x.Service).Cascade.None() and the same for .Demand.

The problem is with inserting ServiceDemandConnection with properly set ServiceRecord and Demand. I get an error: Detail=Key (servicerecord_id)=(8) is not present in table "ServiceRecord". What error states is true. 8 is the ID of TimelineRecord, not ServiceRecord. However, ID of ServiceRecord (TimelineRecord_ID, which is actually not mapped/not accessible in the code) should be used instead. The current mapping hides ServiceRecord.ID.

How should I tell NHibernate to use ID of the subclass table (ServiceRecord), and not of the base class table (TimelineRecord)? NHibernate actually creates a proper constraint in the database, but during runtime it violates it somehow.

Answer 1

You need to either

• map ServiceRecord as separate class not using SubclassMap to use it's ID
• or use ID from base class and do not map it inside SubclassMap

The second approach works because SubclassMap creates a FK relationship between child and parent object so that data is consistent and you have something like

TimeLineRecord
  ID : PK

ServiceRecord extends TimelineRecord:
  TimelineRecord_ID: FK -----> TimeLineRecord.ID

It is still valid to point references to child classess.