1. Does NHibernate support parent/child relationship via multiple fields? Example: Table1.Field1 + Table1.Field2 matches Table2.Field1 + Table2.Field2.
2. I

1. Yes it does, using <composite-id>.
2. It doesn't use a join because you probably didn't tell it to. Use outer-join="true" in the mappings, or a HQL query with 'left join fetch'.

1. Yes it does, using <composite-id>.



Help me with writing map file for them, please.

2. Also I've another one question: does NHibernate support next relationship - One object

I forgot to say that I have another one table:


And if I use <composite-id> for Table1:


Then for Table3 I need to define relation on 2 columns - but I've relation only on one column - How to corect write a map file for this scheme?

From my experience it is easier to work with NHibernate when the database is normalised. This also means that you should use a surrogate primary key (an autoincremented primary key instead of the composite primary key - it makes your life easier. As a consequence your foreign key will be simpler too!

I'm not a database design expert but a FK-FK relationship is not modeling anything. There are 3 type of associations:
1. one-to-one which is modeled with PK-FK or PK-PK
2. one-to-many which is modeled with PK-FK
3 many-to-many which is simplified to two one-to-many by creating a joining table.

O/R mappers are designed to work with this kinds of relationships.

When in my work I encountered FK-FK relationships it was because of poor database design and I transformed them to PK-FK by mapping to a view built specifically to correct that anomaly.

Regards,
Radu