most in memory operations save join and group

Conflicts:

	lib/arel/algebra/extensions/object.rb
	lib/arel/algebra/primitives/value.rb
	lib/arel/engines/memory/relations.rb
	lib/arel/engines/sql/formatters.rb
	lib/arel/engines/sql/primitives.rb
	spec/arel/unit/relations/alias_spec.rb
	spec/arel/unit/relations/array_spec.rb
	spec/arel/unit/relations/order_spec.rb

8 files changed, 59 insertions, 7 deletions

diff --git a/lib/arel/algebra/extensions/array.rb b/lib/arel/algebra/extensions/array.rb
index 5b6d6d6abd..935569a07b 100644
--- a/lib/arel/algebra/extensions/array.rb
+++ b/lib/arel/algebra/extensions/array.rb
@@ -2,4 +2,11 @@ class Array
   def to_hash
     Hash[*flatten]
   end
+  
+  def group_by
+    inject({}) do |groups, element|
+      (groups[yield(element)] ||= []) << element
+      groups
+    end
+  end
 end
\ No newline at end of file
diff --git a/lib/arel/algebra/extensions/hash.rb b/lib/arel/algebra/extensions/hash.rb
index 7472b5aa73..bc97785e62 100644
--- a/lib/arel/algebra/extensions/hash.rb
+++ b/lib/arel/algebra/extensions/hash.rb
@@ -4,4 +4,11 @@ class Hash
       bound.merge(key.bind(relation) => value.bind(relation))
     end
   end
+  
+  def slice(*attributes)
+    inject({}) do |cheese, (key, value)|
+      cheese[key] = value if attributes.include?(key)
+      cheese
+    end
+  end
 end
\ No newline at end of file
diff --git a/lib/arel/algebra/extensions/object.rb b/lib/arel/algebra/extensions/object.rb
index d626407dcb..efdbbf525f 100644
--- a/lib/arel/algebra/extensions/object.rb
+++ b/lib/arel/algebra/extensions/object.rb
@@ -12,4 +12,9 @@ class Object
       self
     end
   end
+
+  def let
+    yield(self)
+  end
 end
+
diff --git a/lib/arel/algebra/primitives.rb b/lib/arel/algebra/primitives.rb
index a4c3169e0b..df8d16a5d5 100644
--- a/lib/arel/algebra/primitives.rb
+++ b/lib/arel/algebra/primitives.rb
@@ -1,4 +1,5 @@
 require 'arel/algebra/primitives/attribute'
+require 'arel/algebra/primitives/ordering'
 require 'arel/algebra/primitives/value'
 require 'arel/algebra/primitives/expression'
 
diff --git a/lib/arel/algebra/primitives/attribute.rb b/lib/arel/algebra/primitives/attribute.rb
index 943c5b030e..7a4411e248 100644
--- a/lib/arel/algebra/primitives/attribute.rb
+++ b/lib/arel/algebra/primitives/attribute.rb
@@ -17,6 +17,10 @@ module Arel
     def aggregation?
       false
     end
+    
+    def inspect
+      "<Attribute #{name}>"
+    end
 
     module Transformations
       def self.included(klass)
@@ -129,5 +133,18 @@ module Arel
       end
     end
     include Expressions
+    
+    module Orderings
+      def asc
+        Ascending.new(self)
+      end
+      
+      def desc
+        Descending.new(self)
+      end
+      
+      alias_method :to_ordering, :asc
+    end
+    include Orderings
   end
 end
diff --git a/lib/arel/algebra/primitives/ordering.rb b/lib/arel/algebra/primitives/ordering.rb
new file mode 100644
index 0000000000..e8d8f97188
--- /dev/null
+++ b/lib/arel/algebra/primitives/ordering.rb
@@ -0,0 +1,18 @@
+module Arel
+  class Ordering
+    attributes :attribute
+    deriving :initialize, :==
+    delegate :relation, :to => :attribute
+    
+    def bind(relation)
+      self.class.new(attribute.bind(relation))
+    end
+    
+    def to_ordering
+      self
+    end
+  end
+  
+  class Ascending  < Ordering; end
+  class Descending < Ordering; end
+end
\ No newline at end of file
diff --git a/lib/arel/algebra/primitives/value.rb b/lib/arel/algebra/primitives/value.rb
index 76c82890d0..e363805140 100644
--- a/lib/arel/algebra/primitives/value.rb
+++ b/lib/arel/algebra/primitives/value.rb
@@ -7,12 +7,8 @@ module Arel
       Value.new(value, relation)
     end
 
-    def aggregation?
-      false
-    end
-
-    def to_attribute
-      value
+    def to_ordering
+      self
     end
   end
 end
diff --git a/lib/arel/algebra/relations/operations/order.rb b/lib/arel/algebra/relations/operations/order.rb
index 05af3fde4d..eccd8bcda0 100644
--- a/lib/arel/algebra/relations/operations/order.rb
+++ b/lib/arel/algebra/relations/operations/order.rb
@@ -10,7 +10,8 @@ module Arel
 
     # TESTME
     def orders
-      (orderings + relation.orders).collect { |o| o.bind(self) }
+      # QUESTION - do we still need relation.orders ?
+      (orderings + relation.orders).collect { |o| o.bind(self) }.collect { |o| o.to_ordering }
     end
   end
 end
\ No newline at end of file