What exactly is Arel in Rails 3.0?

Question

I understand that it is a replacement for ActiveRecord and that it uses objects instead of queries.

But...

why is this better?

will objects/queries

Answer 1

ARel, is unfortunately tied directly to generating SQL and thus is unsuitable for DataMapper's needs.

The way I would put it is that ARel is an explicit query model for ActiveRecord that generates and optimizes SQL queries for RDBMSes.

DataMapper on the other hand is a genuine mapper for data, and can interface with non-relational data stores already. In the future DataMapper is likely to include a separate library called Veritas, which is intended to provide relational functionality to data sourced from ANY data store, not just RDBMSes.