Features - NHibernate versus Writing Custom Object-Relational Mapper

Question

I'm looking for a list of all the features you would have implement in a custom object relational mapper (ORM) to meet all the features of NHibernate.

to start:

1. database portability through different drivers and dialects
2. caching
3. lazy loading
4. custom SQL
5. query interface - LINQ, Criteria, QBE (Query By Example)
6. basic and advanced mapping functionality (ex. discriminator columns, examples)
7. support for transactions and unit of work
8. Multi-Criteria
9. Multi-Query
10. Batching
11. Hooks to supplement/override functionality

<Insert yours Here>

See another list here: 25 Reasons Not To Write Your Own Object Relational Mapper from Ayende Rahien

Answer 1

Some kind of query interface (like linq or Criteria)

Some kind of mapping functionallity

Support for transactions and Unit of work

Answer 2

Multi query,

Batching.

And most importantly: Hooks to supplement/override whatevery functionality that works in ways you did not expect/want/feel like that day.

The last part is one place where NHibernate excels.

Answer 3

Ayende published a near complete list of important ORM features here: http://ayende.com/Blog/archive/2006/05/12/25ReasonsNotToWriteYourOwnObjectRelationalMapper.aspx

An important one that is missing from your list is IsDirty/State Change checking. Identity Map is another important one which enables a lot of the other features such as IsDirty.