We implemented a database abstraction layer called DbGen which generates the actual queries from a common ground.

The key idea is to traverse a tree datastructure which will map to database entities, for instance:

    database my_db {
      int    /basic/i
      float  /basic/f
      string /basic/s
      stored /r
      intmap(stored) /imap
    }

Kind of an ORM but without objects (Opa is purely functional) and without relations when using NoSQL.

But DbGen has support for several types of database including PostgreSQL: See for instance this blog http://www.josetteorama.com/to-sql-from-nosql/