I have two objects with one-to-many relationship with following mapping definition. Whenever, I delete a CostCentre, all LeasePty that
reference it, will have the CostCentre_id set to null and the CostCentre will be deleted. Whereas, I wish the system give me an exception
to tell me that the CostCentre is being referenced and cannot be deleted when I try to delete the CostCentre.

I tried to change the reference to mapping.References(x => x.CostCentre).WithForeignKey().not.nullable. However, this give me an database error when the transaction is actually committed. Can I get an exception at an earlier stage? Thanks!

public class CostCentreMap : IAutoMappingOverride<CostCentre>
{
public void Override(AutoMap<CostCentre> mapping) {

mapping.Id(x => x.Id)
.WithUnsavedValue(0)
.GeneratedBy.Native();

mapping.HasMany(x => x.LeasePties)
.AsBag();

}
}

public class LeasePtyMap : IAutoMappingOverride<LeasePty> {
public void Override(AutoMap<LeasePty> mapping) {

mapping.Id(x => x.Id, "ID")
.WithUnsavedValue(0)
.GeneratedBy.Native();

mapping.Map(x => x.EngAddr1)
.Not.Nullable()
.WithLengthOf(30);

mapping.Map(x => x.EngAddr2)
.Nullable()
.WithLengthOf(30);

mapping.OptimisticLock.Version();
mapping.DynamicUpdate();
mapping.Version(x => x.Version);

/*-------------------------------------- Key --------------------------------------*/
mapping.References(x => x.CostCentre)
.WithForeignKey();
}

}