I agree that composability is an important concern, which is why I like to use what someone above called an "ARM" (abstract relational model) library, instead o

I agree that composability is an important concern, which is why I like to use what someone above called an "ARM" (abstract relational model) library, instead of an ORM. I'd put in that category Squeryl (Scala), jooq (Java), and SQLAlchemy (Python), which all allow building relational queries "on their own terms" and allow for easy composition. Another side benefit is it lets the library authors worry about portability between databases so it's much less of an issue.