Is there a package for object-relational mapping in R?

(By object-relational mapping, I mean what is described here: Wikipedia: Object-relational mapping.)

Here is how I could imagine this work in R : a kind of "virtual data frame" is linked to a database, and returns the results of SQL queries when accessed. For instance, head(virtual_list) would actually return the results of (select * from mapped_table limit 5) on the mapped database.

I have found this post by John Myles White, but there seems to have been no progress in the last 3 years.

Is there a working package that implements this ?

If not,

1. Would it be useful ?
2. What would be the best way to implement it (S4 ?) ?