fluent nhibernate, unable to resolve property: <property>
public T Save(T item)
{
    try
    {
        _session.BeginTransaction();
        int id = (int)_session.Save(item);
        _session.Transaction.Commit();
        return _session.Get<T>(id);
    }
    catch (Exception)
    {
        _session.Transaction.Rollback();
        throw;
    }
}

Id (int, pk, identity)
Field1 (nvarchar)
Field2 (date)
...

TableAId (int, pk) <-- no fk constraint on these tables
Field1 (nvarchar)
Field2 (nvarchar)
Field3 (bit)

public class TableA
{
    public virtual int Id {get;set;}
    public virtual string Field1 {get;set;}
    public virtual DateTime Field2 {get;set;}
    public virtual TableB TableB {get;set;}
}

public class TableB
{
    public virtual int TableAId {get;set;}
    public virtual string Field1 {get;set;}
    public virtual string Field2 {get;set;}
}

public class TableAMap : ClassMap<TableA>
{
    public TableAMap(){
        Id(x => x.Id);
        Map(x => x.Field1);
        Map(x => x.Field2);
        HasOne(x => x.TableB)
         .Cascade.SaveUpdate()
         .Fetch.Join();
    }
}

public class TableBMap : ClassMap<TableB>
{
    public TableBMap()
    {
        Id(x => x.Id, "TableAId").GeneratedBy.Foreign("TableA");
        Map(x => x.Field1);
        Map(x => x.Field2);
        Map(x => x.Field3);
    }
}

public class TableA
{
    public virtual int Id {get;set;}
    public virtual string Field1 {get;set;}
    public virtual DateTime Field2 {get;set;}
    public virtual TableB TableB {get;set;}
    public virtual int TableBId
    {
         get{return TableB.Id;}
         set{}
    }
}

public class TableAMap : ClassMap<TableA>
{
    public TableAMap()
    {
        Id(x => x.Id);
        Map(x => x.Field1);
        Map(x => x.Field2);
        HasOne<TableB>(x => x.TableB)
         .Cascade.SaveUpdate()
         .Fetch.Join()
         .ForeignKey("TableBId");
    }
}

public class TableBMap : ClassMap<TableB>
{
    public TableBMap()
    {
        Id(x => x.Id, "TableAId");
        Map(x => x.Field1);
        Map(x => x.Field2);
        Map(x => x.Field3);
    }
}

public class TableAMap : ClassMap<TableA>
{
    public TableAMap()
    {
        Id(x => x.Id);
        Map(x => x.Field1);
        Map(x => x.Field2);
        HasOne<TableB>(x => x.TableB)
         .Cascade.All()
         .Constrained()
         .Fetch.Join()
         .ForeignKey("TableBId");
    }
}

public class TableBMap : ClassMap<TableB>
{
    public TableBMap()
    {
        Id(x => x.Id, "TableAId").UnsavedValue(0).GeneratedBy.Foreign("TableA");
        Map(x => x.Field1);
        Map(x => x.Field2);
        Map(x => x.Field3);
        HasOne<TableA>(x => x.TableA);
    }
}