arel more nicely supports EXISTS queries

4 files changed, 11 insertions, 8 deletions

diff --git a/lib/arel/nodes/exists.rb b/lib/arel/nodes/exists.rb
index 167a345006..18ba8403b4 100644
--- a/lib/arel/nodes/exists.rb
+++ b/lib/arel/nodes/exists.rb
@@ -1,11 +1,7 @@
 module Arel
   module Nodes
-    class Exists
-      attr_reader :select_stmt
-
-      def initialize select_stmt
-        @select_stmt = select_stmt
-      end
+    class Exists < Arel::Nodes::Function
+      alias :select_stmt :expressions
     end
   end
 end
diff --git a/lib/arel/select_manager.rb b/lib/arel/select_manager.rb
index f2520f38d7..f6738bf26f 100644
--- a/lib/arel/select_manager.rb
+++ b/lib/arel/select_manager.rb
@@ -22,6 +22,12 @@ module Arel
       self
     end
 
+    ###
+    # Produces an Arel::Nodes::Exists node
+    def exists
+      Arel::Nodes::Exists.new @ast
+    end
+
     def where_clauses
       #warn "where_clauses is deprecated" if $VERBOSE
       to_sql = Visitors::ToSql.new @engine
diff --git a/lib/arel/tree_manager.rb b/lib/arel/tree_manager.rb
index ca87def8d6..6176f8a250 100644
--- a/lib/arel/tree_manager.rb
+++ b/lib/arel/tree_manager.rb
@@ -4,7 +4,7 @@ module Arel
     include Arel::Relation
 
     attr_accessor :visitor
-    attr_reader :ast
+    attr_reader :ast, :engine
 
     def initialize engine
       @engine  = engine
diff --git a/lib/arel/visitors/to_sql.rb b/lib/arel/visitors/to_sql.rb
index 3c96b3e259..b6af47cc57 100644
--- a/lib/arel/visitors/to_sql.rb
+++ b/lib/arel/visitors/to_sql.rb
@@ -62,7 +62,8 @@ module Arel
       end
 
       def visit_Arel_Nodes_Exists o
-        "EXISTS (#{visit o.select_stmt})"
+        "EXISTS (#{visit o.select_stmt})#{
+          o.alias ? " AS #{visit o.alias}" : ''}"
       end
 
       def visit_Arel_Nodes_Values o