1 files changed, 63 insertions, 0 deletions
diff --git a/lib/arel/engines/sql/relations/compiler.rb b/lib/arel/engines/sql/relations/compiler.rb
new file mode 100644
index 0000000000..6026fc126f
--- /dev/null
+++ b/lib/arel/engines/sql/relations/compiler.rb
@@ -0,0 +1,63 @@
+module Arel
+  module SqlCompiler
+    class GenericCompiler
+      attr_reader :relation
+
+      def initialize(relation)
+        @relation = relation
+      end
+
+      def select_sql
+        build_query \
+          "SELECT     #{select_clauses.join(', ')}",
+          "FROM       #{from_clauses}",
+          (joins(self)                                   unless joins(self).blank? ),
+          ("WHERE     #{where_clauses.join(" AND ")}"    unless wheres.blank?      ),
+          ("GROUP BY  #{group_clauses.join(', ')}"       unless groupings.blank?   ),
+          ("HAVING    #{having_clauses.join(', ')}"      unless havings.blank?     ),
+          ("ORDER BY  #{order_clauses.join(', ')}"       unless orders.blank?      ),
+          ("LIMIT     #{taken}"                          unless taken.blank?       ),
+          ("OFFSET    #{skipped}"                        unless skipped.blank?     ),
+          ("#{locked}"                                   unless locked.blank?)
+      end
+
+    protected
+      def method_missing(method, *args, &block)
+        relation.send(method, *args, &block)
+      end
+
+      def build_query(*parts)
+        parts.compact.join(" ")
+      end
+
+      def from_clauses
+        sources.blank? ? table_sql(Sql::TableReference.new(relation)) : sources
+      end
+
+      def select_clauses
+        attributes.collect { |a| a.to_sql(Sql::SelectClause.new(relation)) }
+      end
+
+      def where_clauses
+        wheres.collect { |w| w.to_sql(Sql::WhereClause.new(relation)) }
+      end
+
+      def group_clauses
+        groupings.collect { |g| g.to_sql(Sql::GroupClause.new(relation)) }
+      end
+
+      def having_clauses
+        havings.collect { |g| g.to_sql(Sql::HavingClause.new(relation)) }
+      end
+
+      def order_clauses
+        orders.collect { |o| o.to_sql(Sql::OrderClause.new(relation)) }
+      end
+
+      def using_distinct_on?
+        select_clauses.any? { |x| x =~ /DISTINCT ON/ }
+      end
+    end
+
+  end
+end