Convert ActiveRecord::Relations into their ARel AST in Function args. F…

…ixes #17

lib/squeel/visitors/predicate_visitor.rb

@@ -115,6 +115,8 @@ def visit_Squeel_Nodes_Function(o, parent)
           case arg
           when Nodes::Function
             accept(arg, parent)
+          when ActiveRecord::Relation
+            arg.arel.ast
           when Nodes::KeyPath
             can_accept?(arg.endpoint) ? accept(arg, parent) : contextualize(traverse(arg, parent))[arg.endpoint.to_sym]
           when Symbol, Nodes::Stub

spec/squeel/visitors/predicate_visitor_spec.rb

@@ -207,6 +207,13 @@ module Visitors
         predicate.to_sql.should be_like '"people"."id" IN (SELECT  "people"."id" FROM "people"  ORDER BY "people"."id" DESC LIMIT 3)'
       end
 
+      it 'converts ActiveRecord::Relation values in function arguments to their ARel AST' do
+        predicate = @v.accept(dsl{exists(Person.where{name == 'Aric Smith'})})
+        predicate.should be_a Arel::Nodes::NamedFunction
+        predicate.expressions.first.should be_a Arel::Nodes::SelectStatement
+        predicate.to_sql.should be_like "exists(SELECT \"people\".* FROM \"people\"  WHERE \"people\".\"name\" = 'Aric Smith')"
+      end
+
       it "doesn't try to sanitize_sql an array of strings in the value of a Predicate" do
         predicate = @v.accept(dsl{name >> ['Aric Smith', 'Gladyce Kulas']})
         predicate.should be_a Arel::Nodes::In