How to do "where exists" in Arel
How do you do a query that includes a "where exists" in Arel? For example on a query like this to show all the suppliers with at least one order:

    SELECT *
    FROM suppliers
    WHERE EXISTS
      (SELECT *
        FROM orders
        WHERE suppliers.supplier_id = orders.supplier_id);

I see "exists" in the Arel docs http://rubydoc.info/gems/arel/2.0.7/Arel/Nodes/Exists but I'm having trouble using it.
How to do "where exists" in Arel
===

How do you do a query that includes a "where exists" in Arel? For example on a query like this to show all the suppliers with at least one order:

    SELECT *
    FROM suppliers
    WHERE EXISTS
      (SELECT *
        FROM orders
        WHERE suppliers.supplier_id = orders.supplier_id);

I see "exists" in the Arel docs http://rubydoc.info/gems/arel/2.0.7/Arel/Nodes/Exists but I'm having trouble using it.