Are there any books on the principles behind ORMs?

Question

There are a few books about specific ORM products such as Hibernate or Linq to SQL, but I would be quite interested in any material on the more general principles, history etc of ORM.

Do you know of any books, white papers, well researched blog posts etc on this topic?

Thanks /Erik

Answer 1

Try Patterns of Enterprise Application Architecture by Martin Fowler. It's not specifically about ORM's but it shows all the design patterns that a good ORM implements for you.

Answer 2

The fundamental pieces that make up an ORM are described in Martin Fowlers' Patterns of Enterprise Application Architecture

Read all the patterns in the Object Relational categories.

Frans Boumas' blog has plenty of posts that dig deep into ORM theory, you don't have to like his product to appreciate the effort he puts into explaining various concepts and giving strong opinions on all stuff ORM related :)

Anyway, thats a start!