Merge commit 'brynary/master'

Conflicts:

	lib/arel.rb
	lib/arel/session.rb

60 files changed, 1629 insertions, 0 deletions

diff --git a/lib/arel.rb b/lib/arel.rb
new file mode 100644
index 0000000000..54a31b6ed0
--- /dev/null
+++ b/lib/arel.rb
@@ -0,0 +1,13 @@
+$LOAD_PATH.unshift(File.dirname(__FILE__))
+
+require 'rubygems'
+require 'activesupport'
+require 'active_support/dependencies'
+require 'active_support/core_ext/class/attribute_accessors'
+require 'active_support/core_ext/module/delegation'
+require 'activerecord'
+require 'active_record/connection_adapters/abstract/quoting'
+
+require 'arel/algebra'
+require 'arel/engines'
+require 'arel/session'
diff --git a/lib/arel/algebra.rb b/lib/arel/algebra.rb
new file mode 100644
index 0000000000..c206fea0b0
--- /dev/null
+++ b/lib/arel/algebra.rb
@@ -0,0 +1,4 @@
+require 'arel/algebra/extensions'
+require 'arel/algebra/predicates'
+require 'arel/algebra/relations'
+require 'arel/algebra/primitives'
diff --git a/lib/arel/algebra/extensions.rb b/lib/arel/algebra/extensions.rb
new file mode 100644
index 0000000000..bc8edd3274
--- /dev/null
+++ b/lib/arel/algebra/extensions.rb
@@ -0,0 +1,4 @@
+require 'arel/algebra/extensions/object'
+require 'arel/algebra/extensions/class'
+require 'arel/algebra/extensions/symbol'
+require 'arel/algebra/extensions/hash'
diff --git a/lib/arel/algebra/extensions/class.rb b/lib/arel/algebra/extensions/class.rb
new file mode 100644
index 0000000000..520111b90f
--- /dev/null
+++ b/lib/arel/algebra/extensions/class.rb
@@ -0,0 +1,32 @@
+module Arel
+  module ClassExtensions
+    def attributes(*attrs)
+      @attributes = attrs
+      attr_reader *attrs
+    end
+
+    def deriving(*methods)
+      methods.each { |m| derive m }
+    end
+
+    def derive(method_name)
+      methods = {
+        :initialize => "
+          def #{method_name}(#{@attributes.join(',')})
+            #{@attributes.collect { |a| "@#{a} = #{a}" }.join("\n")}
+          end
+        ",
+        :== => "
+          def ==(other)
+            #{name} === other &&
+            #{@attributes.collect { |a| "@#{a} == other.#{a}" }.join(" &&\n")}
+          end
+        "
+      }
+      class_eval methods[method_name], __FILE__, __LINE__
+    end
+    
+    Class.send(:include, self)
+  end
+end
+
diff --git a/lib/arel/algebra/extensions/hash.rb b/lib/arel/algebra/extensions/hash.rb
new file mode 100644
index 0000000000..05c15e7ebe
--- /dev/null
+++ b/lib/arel/algebra/extensions/hash.rb
@@ -0,0 +1,11 @@
+module Arel
+  module HashExtensions
+    def bind(relation)
+      inject({}) do |bound, (key, value)|
+        bound.merge(key.bind(relation) => value.bind(relation))
+      end
+    end
+    
+    Hash.send(:include, self)
+  end
+end
diff --git a/lib/arel/algebra/extensions/object.rb b/lib/arel/algebra/extensions/object.rb
new file mode 100644
index 0000000000..d8c60b5dd5
--- /dev/null
+++ b/lib/arel/algebra/extensions/object.rb
@@ -0,0 +1,17 @@
+module Arel
+  module ObjectExtensions
+    def bind(relation)
+      Arel::Value.new(self, relation)
+    end
+
+    def find_correlate_in(relation)
+      bind(relation)
+    end
+
+    def let
+      yield(self)
+    end
+    
+    Object.send(:include, self)
+  end
+end
diff --git a/lib/arel/algebra/extensions/symbol.rb b/lib/arel/algebra/extensions/symbol.rb
new file mode 100644
index 0000000000..9bb47ef7ab
--- /dev/null
+++ b/lib/arel/algebra/extensions/symbol.rb
@@ -0,0 +1,9 @@
+module Arel
+  module SymbolExtensions
+    def to_attribute(relation)
+      Arel::Attribute.new(relation, self)
+    end
+    
+    Symbol.send(:include, self)
+  end
+end
diff --git a/lib/arel/algebra/predicates.rb b/lib/arel/algebra/predicates.rb
new file mode 100644
index 0000000000..72167c2b27
--- /dev/null
+++ b/lib/arel/algebra/predicates.rb
@@ -0,0 +1,41 @@
+module Arel
+  class Predicate
+    def or(other_predicate)
+      Or.new(self, other_predicate)
+    end
+
+    def and(other_predicate)
+      And.new(self, other_predicate)
+    end
+  end
+
+  class Binary < Predicate
+    attributes :operand1, :operand2
+    deriving :initialize
+
+    def ==(other)
+      self.class === other          and
+      @operand1  ==  other.operand1 and
+      @operand2  ==  other.operand2
+    end
+
+    def bind(relation)
+      self.class.new(operand1.find_correlate_in(relation), operand2.find_correlate_in(relation))
+    end
+  end
+
+  class Equality < Binary
+    def ==(other)
+      Equality === other and
+        ((operand1 == other.operand1 and operand2 == other.operand2) or
+         (operand1 == other.operand2 and operand2 == other.operand1))
+    end
+  end
+
+  class GreaterThanOrEqualTo  < Binary; end
+  class GreaterThan           < Binary; end
+  class LessThanOrEqualTo     < Binary; end
+  class LessThan              < Binary; end
+  class Match                 < Binary; end
+  class In                    < Binary; end
+end
diff --git a/lib/arel/algebra/primitives.rb b/lib/arel/algebra/primitives.rb
new file mode 100644
index 0000000000..df8d16a5d5
--- /dev/null
+++ b/lib/arel/algebra/primitives.rb
@@ -0,0 +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
new file mode 100644
index 0000000000..44a2f41733
--- /dev/null
+++ b/lib/arel/algebra/primitives/attribute.rb
@@ -0,0 +1,150 @@
+require 'set'
+
+module Arel
+  class Attribute
+    attributes :relation, :name, :alias, :ancestor
+    deriving :==
+    delegate :engine, :christener, :to => :relation
+
+    def initialize(relation, name, options = {})
+      @relation, @name, @alias, @ancestor = relation, name, options[:alias], options[:ancestor]
+    end
+
+    def named?(hypothetical_name)
+      (@alias || name).to_s == hypothetical_name.to_s
+    end
+
+    def aggregation?
+      false
+    end
+
+    def inspect
+      "<Attribute #{name}>"
+    end
+
+    module Transformations
+      def self.included(klass)
+        klass.send :alias_method, :eql?, :==
+      end
+
+      def hash
+        @hash ||= history.size + name.hash + relation.hash
+      end
+
+      def as(aliaz = nil)
+        Attribute.new(relation, name, :alias => aliaz, :ancestor => self)
+      end
+
+      def bind(new_relation)
+        relation == new_relation ? self : Attribute.new(new_relation, name, :alias => @alias, :ancestor => self)
+      end
+
+      def to_attribute(relation)
+        bind(relation)
+      end
+    end
+    include Transformations
+
+    module Congruence
+      def history
+        @history ||= [self] + (ancestor ? ancestor.history : [])
+      end
+
+      def join?
+        relation.join?
+      end
+
+      def root
+        history.last
+      end
+
+      def original_relation
+        @original_relation ||= original_attribute.relation
+      end
+
+      def original_attribute
+        @original_attribute ||= history.detect { |a| !a.join? }
+      end
+
+      def find_correlate_in(relation)
+        relation[self] || self
+      end
+
+      def descends_from?(other)
+        history.include?(other)
+      end
+
+      def /(other)
+        other ? (history & other.history).size : 0
+      end
+    end
+    include Congruence
+
+    module Predications
+      def eq(other)
+        Equality.new(self, other)
+      end
+
+      def lt(other)
+        LessThan.new(self, other)
+      end
+
+      def lteq(other)
+        LessThanOrEqualTo.new(self, other)
+      end
+
+      def gt(other)
+        GreaterThan.new(self, other)
+      end
+
+      def gteq(other)
+        GreaterThanOrEqualTo.new(self, other)
+      end
+
+      def matches(regexp)
+        Match.new(self, regexp)
+      end
+
+      def in(array)
+        In.new(self, array)
+      end
+    end
+    include Predications
+
+    module Expressions
+      def count(distinct = false)
+        distinct ?  Distinct.new(self).count :  Count.new(self)
+      end
+
+      def sum
+        Sum.new(self)
+      end
+
+      def maximum
+        Maximum.new(self)
+      end
+
+      def minimum
+        Minimum.new(self)
+      end
+
+      def average
+        Average.new(self)
+      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/expression.rb b/lib/arel/algebra/primitives/expression.rb
new file mode 100644
index 0000000000..875498c282
--- /dev/null
+++ b/lib/arel/algebra/primitives/expression.rb
@@ -0,0 +1,43 @@
+module Arel
+  class Expression < Attribute
+    attributes :attribute, :alias, :ancestor
+    deriving :==
+    delegate :relation, :to => :attribute
+    alias_method :name, :alias
+
+    def initialize(attribute, aliaz = nil, ancestor = nil)
+      @attribute, @alias, @ancestor = attribute, aliaz, ancestor
+    end
+
+    def aggregation?
+      true
+    end
+
+    def inspect
+      "<#{self.class.name} #{attribute.inspect}>"
+    end
+
+    module Transformations
+      def as(aliaz)
+        self.class.new(attribute, aliaz, self)
+      end
+
+      def bind(new_relation)
+        new_relation == relation ? self : self.class.new(attribute.bind(new_relation), @alias, self)
+      end
+
+      def to_attribute(relation)
+        Attribute.new(relation, @alias, :ancestor => self)
+      end
+    end
+    include Transformations
+  end
+
+  class Count    < Expression; end
+  class Distinct < Expression; end
+  class Sum      < Expression; end
+  class Maximum  < Expression; end
+  class Minimum  < Expression; end
+  class Average  < Expression; end
+end
+
diff --git a/lib/arel/algebra/primitives/ordering.rb b/lib/arel/algebra/primitives/ordering.rb
new file mode 100644
index 0000000000..3efb4c6280
--- /dev/null
+++ b/lib/arel/algebra/primitives/ordering.rb
@@ -0,0 +1,23 @@
+module Arel
+  class Ordering
+    delegate :relation, :to => :attribute
+
+    def bind(relation)
+      self.class.new(attribute.bind(relation))
+    end
+
+    def to_ordering
+      self
+    end
+  end
+
+  class Ascending  < Ordering
+    attributes :attribute
+    deriving :initialize, :==
+  end
+  
+  class Descending < Ordering
+    attributes :attribute
+    deriving :initialize, :==
+  end
+end
diff --git a/lib/arel/algebra/primitives/value.rb b/lib/arel/algebra/primitives/value.rb
new file mode 100644
index 0000000000..e363805140
--- /dev/null
+++ b/lib/arel/algebra/primitives/value.rb
@@ -0,0 +1,14 @@
+module Arel
+  class Value
+    attributes :value, :relation
+    deriving :initialize, :==
+
+    def bind(relation)
+      Value.new(value, relation)
+    end
+
+    def to_ordering
+      self
+    end
+  end
+end
diff --git a/lib/arel/algebra/relations.rb b/lib/arel/algebra/relations.rb
new file mode 100644
index 0000000000..f9fa24ba25
--- /dev/null
+++ b/lib/arel/algebra/relations.rb
@@ -0,0 +1,14 @@
+require 'arel/algebra/relations/relation'
+require 'arel/algebra/relations/utilities/compound'
+require 'arel/algebra/relations/utilities/nil'
+require 'arel/algebra/relations/utilities/externalization'
+require 'arel/algebra/relations/row'
+require 'arel/algebra/relations/writes'
+require 'arel/algebra/relations/operations/alias'
+require 'arel/algebra/relations/operations/group'
+require 'arel/algebra/relations/operations/join'
+require 'arel/algebra/relations/operations/order'
+require 'arel/algebra/relations/operations/project'
+require 'arel/algebra/relations/operations/where'
+require 'arel/algebra/relations/operations/skip'
+require 'arel/algebra/relations/operations/take'
diff --git a/lib/arel/algebra/relations/operations/alias.rb b/lib/arel/algebra/relations/operations/alias.rb
new file mode 100644
index 0000000000..0331d98b85
--- /dev/null
+++ b/lib/arel/algebra/relations/operations/alias.rb
@@ -0,0 +1,7 @@
+module Arel
+  class Alias < Compound
+    attributes :relation
+    deriving :initialize
+    alias_method :==, :equal?
+  end
+end
diff --git a/lib/arel/algebra/relations/operations/group.rb b/lib/arel/algebra/relations/operations/group.rb
new file mode 100644
index 0000000000..2bfc42214b
--- /dev/null
+++ b/lib/arel/algebra/relations/operations/group.rb
@@ -0,0 +1,12 @@
+module Arel
+  class Group < Compound
+    attributes :relation, :groupings
+    deriving :==
+
+    def initialize(relation, *groupings, &block)
+      @relation = relation
+      @groupings = (groupings + arguments_from_block(relation, &block)) \
+        .collect { |g| g.bind(relation) }
+    end
+  end
+end
diff --git a/lib/arel/algebra/relations/operations/join.rb b/lib/arel/algebra/relations/operations/join.rb
new file mode 100644
index 0000000000..e9320f28e1
--- /dev/null
+++ b/lib/arel/algebra/relations/operations/join.rb
@@ -0,0 +1,64 @@
+module Arel
+  class Join < Relation
+    attributes :relation1, :relation2, :predicates
+    deriving :==
+    delegate :name, :to => :relation1
+
+    def initialize(relation1, relation2 = Nil.instance, *predicates)
+      @relation1, @relation2, @predicates = relation1, relation2, predicates
+    end
+
+    def hash
+      @hash ||= :relation1.hash
+    end
+
+    def eql?(other)
+      self == other
+    end
+
+    def attributes
+      @attributes ||= (relation1.externalize.attributes +
+        relation2.externalize.attributes).collect { |a| a.bind(self) }
+    end
+
+    def wheres
+      # TESTME bind to self?
+      relation1.externalize.wheres
+    end
+
+    def ons
+      @ons ||= @predicates.collect { |p| p.bind(self) }
+    end
+
+    # TESTME
+    def externalizable?
+      relation1.externalizable? or relation2.externalizable?
+    end
+
+    def join?
+      true
+    end
+
+    def engine
+      relation1.engine != relation2.engine ? Memory::Engine.new : relation1.engine
+    end
+  end
+
+  class InnerJoin  < Join; end
+  class OuterJoin  < Join; end
+  class StringJoin < Join
+    def attributes
+      relation1.externalize.attributes
+    end
+
+    def engine
+      relation1.engine
+    end
+  end
+
+  class Relation
+    def join?
+      false
+    end
+  end
+end
diff --git a/lib/arel/algebra/relations/operations/order.rb b/lib/arel/algebra/relations/operations/order.rb
new file mode 100644
index 0000000000..a589b56997
--- /dev/null
+++ b/lib/arel/algebra/relations/operations/order.rb
@@ -0,0 +1,18 @@
+module Arel
+  class Order < Compound
+    attributes :relation, :orderings
+    deriving :==
+
+    def initialize(relation, *orderings, &block)
+      @relation = relation
+      @orderings = (orderings + arguments_from_block(relation, &block)) \
+        .collect { |o| o.bind(relation) }
+    end
+
+    # TESTME
+    def orders
+      # QUESTION - do we still need relation.orders ?
+      (orderings + relation.orders).collect { |o| o.bind(self) }.collect { |o| o.to_ordering }
+    end
+  end
+end
diff --git a/lib/arel/algebra/relations/operations/project.rb b/lib/arel/algebra/relations/operations/project.rb
new file mode 100644
index 0000000000..223d320e22
--- /dev/null
+++ b/lib/arel/algebra/relations/operations/project.rb
@@ -0,0 +1,20 @@
+module Arel
+  class Project < Compound
+    attributes :relation, :projections
+    deriving :==
+
+    def initialize(relation, *projections, &block)
+      @relation = relation
+      @projections = (projections + arguments_from_block(relation, &block)) \
+        .collect { |p| p.bind(relation) }
+    end
+
+    def attributes
+      @attributes ||= projections.collect { |p| p.bind(self) }
+    end
+
+    def externalizable?
+      attributes.any?(&:aggregation?) or relation.externalizable?
+    end
+  end
+end
diff --git a/lib/arel/algebra/relations/operations/skip.rb b/lib/arel/algebra/relations/operations/skip.rb
new file mode 100644
index 0000000000..689e06e1c3
--- /dev/null
+++ b/lib/arel/algebra/relations/operations/skip.rb
@@ -0,0 +1,6 @@
+module Arel
+  class Skip < Compound
+    attributes :relation, :skipped
+    deriving :initialize, :==
+  end
+end
diff --git a/lib/arel/algebra/relations/operations/take.rb b/lib/arel/algebra/relations/operations/take.rb
new file mode 100644
index 0000000000..eb32ec492e
--- /dev/null
+++ b/lib/arel/algebra/relations/operations/take.rb
@@ -0,0 +1,10 @@
+module Arel
+  class Take < Compound
+    attributes :relation, :taken
+    deriving :initialize, :==
+
+    def externalizable?
+      true
+    end
+  end
+end
diff --git a/lib/arel/algebra/relations/operations/where.rb b/lib/arel/algebra/relations/operations/where.rb
new file mode 100644
index 0000000000..608aaeb4b7
--- /dev/null
+++ b/lib/arel/algebra/relations/operations/where.rb
@@ -0,0 +1,16 @@
+module Arel
+  class Where < Compound
+    attributes :relation, :predicate
+    deriving :==
+
+    def initialize(relation, *predicates, &block)
+      predicate = block_given?? yield(relation) : predicates.shift
+      @relation = predicates.empty?? relation : Where.new(relation, *predicates)
+      @predicate = predicate.bind(@relation)
+    end
+
+    def wheres
+      @wheres ||= (relation.wheres + [predicate]).collect { |p| p.bind(self) }
+    end
+  end
+end
diff --git a/lib/arel/algebra/relations/relation.rb b/lib/arel/algebra/relations/relation.rb
new file mode 100644
index 0000000000..9fdac26528
--- /dev/null
+++ b/lib/arel/algebra/relations/relation.rb
@@ -0,0 +1,136 @@
+module Arel
+  class Relation
+    attr_reader :count
+
+    def session
+      Session.new
+    end
+
+    def call
+      engine.read(self)
+    end
+
+    def bind(relation)
+      self
+    end
+
+    module Enumerable
+      include ::Enumerable
+
+      def each(&block)
+        session.read(self).each(&block)
+      end
+
+      def first
+        session.read(self).first
+      end
+    end
+    include Enumerable
+
+    module Operable
+      def join(other_relation = nil, join_class = InnerJoin)
+        case other_relation
+        when String
+          StringJoin.new(self, other_relation)
+        when Relation
+          JoinOperation.new(join_class, self, other_relation)
+        else
+          self
+        end
+      end
+
+      def outer_join(other_relation = nil)
+        join(other_relation, OuterJoin)
+      end
+
+      [:where, :project, :order, :take, :skip, :group].each do |operation_name|
+        class_eval <<-OPERATION, __FILE__, __LINE__
+          def #{operation_name}(*arguments, &block)
+            arguments.all?(&:blank?) && !block_given?? self : #{operation_name.to_s.classify}.new(self, *arguments, &block)
+          end
+        OPERATION
+      end
+
+      def alias
+        Alias.new(self)
+      end
+
+      module Writable
+        def insert(record)
+          session.create Insert.new(self, record)
+        end
+
+        def update(assignments)
+          session.update Update.new(self, assignments)
+        end
+
+        def delete
+          session.delete Deletion.new(self)
+        end
+      end
+      include Writable
+
+      JoinOperation = Struct.new(:join_class, :relation1, :relation2) do
+        def on(*predicates)
+          join_class.new(relation1, relation2, *predicates)
+        end
+      end
+    end
+    include Operable
+
+    module AttributeAccessable
+      def [](index)
+        case index
+        when Symbol, String
+          find_attribute_matching_name(index)
+        when Attribute, Expression
+          find_attribute_matching_attribute(index)
+        when ::Array
+          # TESTME
+          index.collect { |i| self[i] }
+        end
+      end
+
+      def find_attribute_matching_name(name)
+        attributes.detect { |a| a.named?(name) }
+      end
+
+      def find_attribute_matching_attribute(attribute)
+        matching_attributes(attribute).max do |a1, a2|
+          (a1.original_attribute / attribute) <=> (a2.original_attribute / attribute)
+        end
+      end
+
+      def position_of(attribute)
+        (@position_of ||= Hash.new do |h, attribute|
+          h[attribute] = attributes.index(self[attribute])
+        end)[attribute]
+      end
+
+      private
+      def matching_attributes(attribute)
+        (@matching_attributes ||= attributes.inject({}) do |hash, a|
+          (hash[a.root] ||= []) << a
+          hash
+        end)[attribute.root] || []
+      end
+
+      def has_attribute?(attribute)
+        !matching_attributes(attribute).empty?
+      end
+    end
+    include AttributeAccessable
+
+    module DefaultOperations
+      def attributes;             []  end
+      def wheres;                 []  end
+      def orders;                 []  end
+      def inserts;                []  end
+      def groupings;              []  end
+      def joins(formatter = nil); nil end # FIXME
+      def taken;                  nil end
+      def skipped;                nil end
+    end
+    include DefaultOperations
+  end
+end
diff --git a/lib/arel/algebra/relations/row.rb b/lib/arel/algebra/relations/row.rb
new file mode 100644
index 0000000000..3158557448
--- /dev/null
+++ b/lib/arel/algebra/relations/row.rb
@@ -0,0 +1,26 @@
+module Arel
+  class Row
+    attributes :relation, :tuple
+    deriving :==, :initialize
+
+    def [](attribute)
+      attribute.type_cast(tuple[relation.position_of(attribute)])
+    end
+
+    def slice(*attributes)
+      Row.new(relation, attributes.inject([]) do |cheese, attribute|
+        # FIXME TESTME method chaining
+        cheese << tuple[relation.relation.position_of(attribute)]
+        cheese
+      end)
+    end
+
+    def bind(relation)
+      Row.new(relation, tuple)
+    end
+
+    def combine(other, relation)
+      Row.new(relation, tuple + other.tuple)
+    end
+  end
+end
diff --git a/lib/arel/algebra/relations/utilities/compound.rb b/lib/arel/algebra/relations/utilities/compound.rb
new file mode 100644
index 0000000000..5e775618f1
--- /dev/null
+++ b/lib/arel/algebra/relations/utilities/compound.rb
@@ -0,0 +1,30 @@
+module Arel
+  class Compound < Relation
+    attr_reader :relation
+    delegate :joins, :join?, :inserts, :taken, :skipped, :name, :externalizable?,
+             :column_for, :engine,
+             :to => :relation
+
+    [:attributes, :wheres, :groupings, :orders].each do |operation_name|
+      class_eval <<-OPERATION, __FILE__, __LINE__
+        def #{operation_name}
+          @#{operation_name} ||= relation.#{operation_name}.collect { |o| o.bind(self) }
+        end
+      OPERATION
+    end
+
+    def hash
+      @hash ||= :relation.hash
+    end
+
+    def eql?(other)
+      self == other
+    end
+
+  private
+
+    def arguments_from_block(relation, &block)
+      block_given?? [yield(relation)] : []
+    end
+  end
+end
diff --git a/lib/arel/algebra/relations/utilities/externalization.rb b/lib/arel/algebra/relations/utilities/externalization.rb
new file mode 100644
index 0000000000..13758ccec9
--- /dev/null
+++ b/lib/arel/algebra/relations/utilities/externalization.rb
@@ -0,0 +1,24 @@
+module Arel
+  class Externalization < Compound
+    attributes :relation
+    deriving :initialize, :==
+
+    def wheres
+      []
+    end
+
+    def attributes
+      @attributes ||= relation.attributes.collect { |a| a.to_attribute(self) }
+    end
+  end
+
+  class Relation
+    def externalize
+      @externalized ||= externalizable?? Externalization.new(self) : self
+    end
+
+    def externalizable?
+      false
+    end
+  end
+end
diff --git a/lib/arel/algebra/relations/utilities/nil.rb b/lib/arel/algebra/relations/utilities/nil.rb
new file mode 100644
index 0000000000..6a9d678c45
--- /dev/null
+++ b/lib/arel/algebra/relations/utilities/nil.rb
@@ -0,0 +1,7 @@
+require 'singleton'
+
+module Arel
+  class Nil < Relation
+    include Singleton
+  end
+end
diff --git a/lib/arel/algebra/relations/writes.rb b/lib/arel/algebra/relations/writes.rb
new file mode 100644
index 0000000000..d344987915
--- /dev/null
+++ b/lib/arel/algebra/relations/writes.rb
@@ -0,0 +1,36 @@
+module Arel
+  class Deletion < Compound
+    attributes :relation
+    deriving :initialize, :==
+
+    def call
+      engine.delete(self)
+    end
+  end
+
+  class Insert < Compound
+    attributes :relation, :record
+    deriving :==
+
+    def initialize(relation, record)
+      @relation, @record = relation, record.bind(relation)
+    end
+
+    def call
+      engine.create(self)
+    end
+  end
+
+  class Update < Compound
+    attributes :relation, :assignments
+    deriving :==
+
+    def initialize(relation, assignments)
+      @relation, @assignments = relation, assignments.bind(relation)
+    end
+
+    def call
+      engine.update(self)
+    end
+  end
+end
diff --git a/lib/arel/engines.rb b/lib/arel/engines.rb
new file mode 100644
index 0000000000..cd848d83e2
--- /dev/null
+++ b/lib/arel/engines.rb
@@ -0,0 +1,2 @@
+require 'arel/engines/sql'
+require 'arel/engines/memory'
diff --git a/lib/arel/engines/memory.rb b/lib/arel/engines/memory.rb
new file mode 100644
index 0000000000..9e7193ef13
--- /dev/null
+++ b/lib/arel/engines/memory.rb
@@ -0,0 +1,4 @@
+require 'arel/engines/memory/relations'
+require 'arel/engines/memory/primitives'
+require 'arel/engines/memory/engine'
+require 'arel/engines/memory/predicates'
diff --git a/lib/arel/engines/memory/engine.rb b/lib/arel/engines/memory/engine.rb
new file mode 100644
index 0000000000..c7ac9422d4
--- /dev/null
+++ b/lib/arel/engines/memory/engine.rb
@@ -0,0 +1,16 @@
+module Arel
+  module Memory
+    class Engine
+      module CRUD
+        def read(relation)
+          relation.eval
+        end
+
+        def create(relation)
+          relation.eval
+        end
+      end
+      include CRUD
+    end
+  end
+end
diff --git a/lib/arel/engines/memory/predicates.rb b/lib/arel/engines/memory/predicates.rb
new file mode 100644
index 0000000000..03d4f25b0a
--- /dev/null
+++ b/lib/arel/engines/memory/predicates.rb
@@ -0,0 +1,35 @@
+module Arel
+  class Binary < Predicate
+    def eval(row)
+      operand1.eval(row).send(operator, operand2.eval(row))
+    end
+  end
+
+  class Equality < Binary
+    def operator; :== end
+  end
+
+  class GreaterThanOrEqualTo < Binary
+    def operator; :>= end
+  end
+
+  class GreaterThan < Binary
+    def operator; :> end
+  end
+
+  class LessThanOrEqualTo < Binary
+    def operator; :<= end
+  end
+
+  class LessThan < Binary
+    def operator; :< end
+  end
+
+  class Match < Binary
+    def operator; :=~ end
+  end
+
+  class In < Binary
+    def operator; :include? end
+  end
+end
diff --git a/lib/arel/engines/memory/primitives.rb b/lib/arel/engines/memory/primitives.rb
new file mode 100644
index 0000000000..935b34f5ee
--- /dev/null
+++ b/lib/arel/engines/memory/primitives.rb
@@ -0,0 +1,27 @@
+module Arel
+  class Attribute
+    def eval(row)
+      row[self]
+    end
+  end
+
+  class Value
+    def eval(row)
+      value
+    end
+  end
+
+  class Ordering
+    def eval(row1, row2)
+      (attribute.eval(row1) <=> attribute.eval(row2)) * direction
+    end
+  end
+
+  class Descending < Ordering
+    def direction; -1 end
+  end
+
+  class Ascending < Ordering
+    def direction; 1 end
+  end
+end
diff --git a/lib/arel/engines/memory/relations.rb b/lib/arel/engines/memory/relations.rb
new file mode 100644
index 0000000000..c67af2d63b
--- /dev/null
+++ b/lib/arel/engines/memory/relations.rb
@@ -0,0 +1,5 @@
+require 'arel/engines/memory/relations/array'
+require 'arel/engines/memory/relations/operations'
+require 'arel/engines/memory/relations/writes'
+require 'arel/engines/memory/relations/compound'
+
diff --git a/lib/arel/engines/memory/relations/array.rb b/lib/arel/engines/memory/relations/array.rb
new file mode 100644
index 0000000000..5e7c0a4ab1
--- /dev/null
+++ b/lib/arel/engines/memory/relations/array.rb
@@ -0,0 +1,25 @@
+module Arel
+  class Array < Relation
+    attributes :array,  :attribute_names
+    include Recursion::BaseCase
+    deriving :==, :initialize
+
+    def engine
+      @engine ||= Memory::Engine.new
+    end
+
+    def attributes
+      @attributes ||= @attribute_names.collect do |name|
+        name.to_attribute(self)
+      end
+    end
+
+    def format(attribute, value)
+      value
+    end
+
+    def eval
+      @array.collect { |r| Row.new(self, r) }
+    end
+  end
+end
diff --git a/lib/arel/engines/memory/relations/compound.rb b/lib/arel/engines/memory/relations/compound.rb
new file mode 100644
index 0000000000..6dda92a6a1
--- /dev/null
+++ b/lib/arel/engines/memory/relations/compound.rb
@@ -0,0 +1,9 @@
+module Arel
+  class Compound < Relation
+    delegate :array, :to => :relation
+
+    def unoperated_rows
+      relation.call.collect { |row| row.bind(self) }
+    end
+  end
+end
diff --git a/lib/arel/engines/memory/relations/operations.rb b/lib/arel/engines/memory/relations/operations.rb
new file mode 100644
index 0000000000..8e01938360
--- /dev/null
+++ b/lib/arel/engines/memory/relations/operations.rb
@@ -0,0 +1,61 @@
+module Arel
+  class Where < Compound
+    def eval
+      unoperated_rows.select { |row| predicate.eval(row) }
+    end
+  end
+
+  class Order < Compound
+    def eval
+      unoperated_rows.sort do |row1, row2|
+        ordering = orderings.detect { |o| o.eval(row1, row2) != 0 } || orderings.last
+        ordering.eval(row1, row2)
+      end
+    end
+  end
+
+  class Project < Compound
+    def eval
+      unoperated_rows.collect { |r| r.slice(*projections) }
+    end
+  end
+
+  class Take < Compound
+    def eval
+      unoperated_rows[0, taken]
+    end
+  end
+
+  class Skip < Compound
+    def eval
+      unoperated_rows[skipped..-1]
+    end
+  end
+
+  class Group < Compound
+    def eval
+      raise NotImplementedError
+    end
+  end
+
+  class Alias < Compound
+    def eval
+      unoperated_rows
+    end
+  end
+
+  class Join < Relation
+    def eval
+      result = []
+      relation1.call.each do |row1|
+        relation2.call.each do |row2|
+          combined_row = row1.combine(row2, self)
+          if predicates.all? { |p| p.eval(combined_row) }
+            result << combined_row
+          end
+        end
+      end
+      result
+    end
+  end
+end
diff --git a/lib/arel/engines/memory/relations/writes.rb b/lib/arel/engines/memory/relations/writes.rb
new file mode 100644
index 0000000000..12c4f36c0d
--- /dev/null
+++ b/lib/arel/engines/memory/relations/writes.rb
@@ -0,0 +1,7 @@
+module Arel
+  class Insert < Compound
+    def eval
+      unoperated_rows + [Row.new(self, record.values.collect(&:value))]
+    end
+  end
+end
diff --git a/lib/arel/engines/sql.rb b/lib/arel/engines/sql.rb
new file mode 100644
index 0000000000..f31cfc7dac
--- /dev/null
+++ b/lib/arel/engines/sql.rb
@@ -0,0 +1,7 @@
+require 'arel/engines/sql/engine'
+require 'arel/engines/sql/relations'
+require 'arel/engines/sql/primitives'
+require 'arel/engines/sql/predicates'
+require 'arel/engines/sql/formatters'
+require 'arel/engines/sql/extensions'
+require 'arel/engines/sql/christener'
diff --git a/lib/arel/engines/sql/christener.rb b/lib/arel/engines/sql/christener.rb
new file mode 100644
index 0000000000..c1c9325208
--- /dev/null
+++ b/lib/arel/engines/sql/christener.rb
@@ -0,0 +1,13 @@
+module Arel
+  module Sql
+    class Christener
+      def name_for(relation)
+        @used_names ||= Hash.new(0)
+        (@relation_names ||= Hash.new do |hash, relation|
+          @used_names[name = relation.name] += 1
+          hash[relation] = name + (@used_names[name] > 1 ? "_#{@used_names[name]}" : '')
+        end)[relation.table]
+      end
+    end
+  end
+end
diff --git a/lib/arel/engines/sql/engine.rb b/lib/arel/engines/sql/engine.rb
new file mode 100644
index 0000000000..7d2926040c
--- /dev/null
+++ b/lib/arel/engines/sql/engine.rb
@@ -0,0 +1,37 @@
+module Arel
+  module Sql
+    class Engine
+      def initialize(ar = nil)
+        @ar = ar
+      end
+
+      def connection
+        @ar.connection
+      end
+
+      def method_missing(method, *args, &block)
+        @ar.connection.send(method, *args, &block)
+      end
+
+      module CRUD
+        def create(relation)
+          connection.insert(relation.to_sql)
+        end
+
+        def read(relation)
+          rows = connection.select_rows(relation.to_sql)
+          Array.new(rows, relation.attributes)
+        end
+
+        def update(relation)
+          connection.update(relation.to_sql)
+        end
+
+        def delete(relation)
+          connection.delete(relation.to_sql)
+        end
+      end
+      include CRUD
+    end
+  end
+end
diff --git a/lib/arel/engines/sql/extensions.rb b/lib/arel/engines/sql/extensions.rb
new file mode 100644
index 0000000000..1ea31bc140
--- /dev/null
+++ b/lib/arel/engines/sql/extensions.rb
@@ -0,0 +1,4 @@
+require 'arel/engines/sql/extensions/object'
+require 'arel/engines/sql/extensions/array'
+require 'arel/engines/sql/extensions/range'
+require 'arel/engines/sql/extensions/nil_class'
diff --git a/lib/arel/engines/sql/extensions/array.rb b/lib/arel/engines/sql/extensions/array.rb
new file mode 100644
index 0000000000..7f15179721
--- /dev/null
+++ b/lib/arel/engines/sql/extensions/array.rb
@@ -0,0 +1,16 @@
+module Arel
+  module Sql
+    module ArrayExtensions
+      def to_sql(formatter = nil)
+        "(" + collect { |e| e.to_sql(formatter) }.join(', ') + ")"
+      end
+
+      def inclusion_predicate_sql
+        "IN"
+      end
+      
+      Array.send(:include, self)
+    end
+  end
+end
+
diff --git a/lib/arel/engines/sql/extensions/nil_class.rb b/lib/arel/engines/sql/extensions/nil_class.rb
new file mode 100644
index 0000000000..8c335f904a
--- /dev/null
+++ b/lib/arel/engines/sql/extensions/nil_class.rb
@@ -0,0 +1,11 @@
+module Arel
+  module Sql
+    module NilClassExtensions
+      def equality_predicate_sql
+        'IS'
+      end
+      
+      NilClass.send(:include, self)
+    end
+  end
+end
diff --git a/lib/arel/engines/sql/extensions/object.rb b/lib/arel/engines/sql/extensions/object.rb
new file mode 100644
index 0000000000..8fe63dba2f
--- /dev/null
+++ b/lib/arel/engines/sql/extensions/object.rb
@@ -0,0 +1,15 @@
+module Arel
+  module Sql
+    module ObjectExtensions
+      def to_sql(formatter)
+        formatter.scalar self
+      end
+
+      def equality_predicate_sql
+        '='
+      end
+      
+      Object.send(:include, self)
+    end
+  end
+end
diff --git a/lib/arel/engines/sql/extensions/range.rb b/lib/arel/engines/sql/extensions/range.rb
new file mode 100644
index 0000000000..25bf1d01da
--- /dev/null
+++ b/lib/arel/engines/sql/extensions/range.rb
@@ -0,0 +1,15 @@
+module Arel
+  module Sql
+    module RangeExtensions
+      def to_sql(formatter = nil)
+        formatter.range self.begin, self.end
+      end
+
+      def inclusion_predicate_sql
+        "BETWEEN"
+      end
+      
+      Range.send(:include, self)
+    end
+  end
+end
diff --git a/lib/arel/engines/sql/formatters.rb b/lib/arel/engines/sql/formatters.rb
new file mode 100644
index 0000000000..ae80feb18e
--- /dev/null
+++ b/lib/arel/engines/sql/formatters.rb
@@ -0,0 +1,113 @@
+module Arel
+  module Sql
+    class Formatter
+      attr_reader :environment
+      delegate :christener, :engine, :to => :environment
+      delegate :name_for, :to => :christener
+      delegate :quote_table_name, :quote_column_name, :quote, :to => :engine
+
+      def initialize(environment)
+        @environment = environment
+      end
+    end
+
+    class SelectClause < Formatter
+      def attribute(attribute)
+        # FIXME this should check that the column exists
+        "#{quote_table_name(name_for(attribute.original_relation))}.#{quote_column_name(attribute.name)}" +
+        (attribute.alias ? " AS #{quote(attribute.alias.to_s)}" : "")
+      end
+
+      def expression(expression)
+        if expression.function_sql == "DISTINCT"
+          "#{expression.function_sql} #{expression.attribute.to_sql(self)}" +
+          (expression.alias ? " AS #{quote_column_name(expression.alias)}" : '')
+        else
+          "#{expression.function_sql}(#{expression.attribute.to_sql(self)})" +
+          (expression.alias ? " AS #{quote_column_name(expression.alias)}" : " AS #{expression.function_sql.to_s.downcase}_id")
+        end
+      end
+
+      def select(select_sql, table)
+        "(#{select_sql}) AS #{quote_table_name(name_for(table))}"
+      end
+
+      def value(value)
+        value
+      end
+    end
+
+    class PassThrough < Formatter
+      def value(value)
+        value
+      end
+    end
+
+    class WhereClause < PassThrough
+    end
+
+    class OrderClause < PassThrough
+      def ordering(ordering)
+        "#{quote_table_name(name_for(ordering.attribute.original_relation))}.#{quote_column_name(ordering.attribute.name)} #{ordering.direction_sql}"
+      end
+    end
+
+    class GroupClause < PassThrough
+      def attribute(attribute)
+        "#{quote_table_name(name_for(attribute.original_relation))}.#{quote_column_name(attribute.name)}"
+      end
+    end
+
+    class WhereCondition < Formatter
+      def attribute(attribute)
+        "#{quote_table_name(name_for(attribute.original_relation))}.#{quote_column_name(attribute.name)}"
+      end
+
+      def expression(expression)
+        "#{expression.function_sql}(#{expression.attribute.to_sql(self)})"
+      end
+
+      def value(value)
+        value.to_sql(self)
+      end
+
+      def scalar(value, column = nil)
+        quote(value, column)
+      end
+
+      def select(select_sql, table)
+        "(#{select_sql})"
+      end
+    end
+
+    class SelectStatement < Formatter
+      def select(select_sql, table)
+        select_sql
+      end
+    end
+
+    class TableReference < Formatter
+      def select(select_sql, table)
+        "(#{select_sql}) AS #{quote_table_name(name_for(table))}"
+      end
+
+      def table(table)
+        quote_table_name(table.name) +
+        (table.name != name_for(table) ? " AS " + quote_table_name(name_for(table)) : '')
+      end
+    end
+
+    class Attribute < WhereCondition
+      def scalar(scalar)
+        quote(scalar, environment.column)
+      end
+
+      def range(left, right)
+        "#{left} AND #{right}"
+      end
+    end
+
+    class Value < WhereCondition
+    end
+  end
+end
diff --git a/lib/arel/engines/sql/predicates.rb b/lib/arel/engines/sql/predicates.rb
new file mode 100644
index 0000000000..b84c183c1d
--- /dev/null
+++ b/lib/arel/engines/sql/predicates.rb
@@ -0,0 +1,51 @@
+module Arel
+  class Binary < Predicate
+    def to_sql(formatter = nil)
+      "#{operand1.to_sql} #{predicate_sql} #{operand1.format(operand2)}"
+    end
+  end
+
+  class CompoundPredicate < Binary
+    def to_sql(formatter = nil)
+      "(#{operand1.to_sql(formatter)} #{predicate_sql} #{operand2.to_sql(formatter)})"
+    end
+  end
+
+  class Or < CompoundPredicate
+    def predicate_sql; "OR" end
+  end
+
+  class And < CompoundPredicate
+    def predicate_sql; "AND" end
+  end
+
+  class Equality < Binary
+    def predicate_sql
+      operand2.equality_predicate_sql
+    end
+  end
+
+  class GreaterThanOrEqualTo < Binary
+    def predicate_sql; '>=' end
+  end
+
+  class GreaterThan < Binary
+    def predicate_sql; '>' end
+  end
+
+  class LessThanOrEqualTo < Binary
+    def predicate_sql; '<=' end
+  end
+
+  class LessThan < Binary
+    def predicate_sql; '<' end
+  end
+
+  class Match < Binary
+    def predicate_sql; 'LIKE' end
+  end
+
+  class In < Binary
+    def predicate_sql; operand2.inclusion_predicate_sql end
+  end
+end
diff --git a/lib/arel/engines/sql/primitives.rb b/lib/arel/engines/sql/primitives.rb
new file mode 100644
index 0000000000..bb3bed78e6
--- /dev/null
+++ b/lib/arel/engines/sql/primitives.rb
@@ -0,0 +1,85 @@
+module Arel
+  class SqlLiteral < String
+    def relation
+      nil
+    end
+    
+    def to_sql(formatter = nil)
+      self
+    end
+  end
+
+  class Attribute
+    def column
+      original_relation.column_for(self)
+    end
+
+    def type_cast(value)
+      root.relation.format(self, value)
+    end
+
+    def format(object)
+      object.to_sql(Sql::Attribute.new(self))
+    end
+
+    def to_sql(formatter = Sql::WhereCondition.new(relation))
+      formatter.attribute self
+    end
+  end
+
+  class Value
+    delegate :inclusion_predicate_sql, :equality_predicate_sql, :to => :value
+
+    def to_sql(formatter = Sql::WhereCondition.new(relation))
+      formatter.value value
+    end
+
+    def format(object)
+      object.to_sql(Sql::Value.new(relation))
+    end
+  end
+
+  class Ordering
+    def to_sql(formatter = Sql::OrderClause.new(relation))
+      formatter.ordering self
+    end
+  end
+
+  class Ascending < Ordering
+    def direction_sql; 'ASC' end
+  end
+
+  class Descending < Ordering
+    def direction_sql; 'DESC' end
+  end
+
+  class Expression < Attribute
+    def to_sql(formatter = Sql::SelectClause.new(relation))
+      formatter.expression self
+    end
+  end
+
+  class Count < Expression
+    def function_sql; 'COUNT' end
+  end
+
+  class Distinct < Expression
+    def function_sql; 'DISTINCT' end
+  end
+
+  class Sum < Expression
+    def function_sql; 'SUM' end
+  end
+
+  class Maximum < Expression
+    def function_sql; 'MAX' end
+  end
+
+  class Minimum < Expression
+    def function_sql; 'MIN' end
+  end
+
+  class Average < Expression
+    def function_sql; 'AVG' end
+  end
+end
diff --git a/lib/arel/engines/sql/relations.rb b/lib/arel/engines/sql/relations.rb
new file mode 100644
index 0000000000..8360a1f806
--- /dev/null
+++ b/lib/arel/engines/sql/relations.rb
@@ -0,0 +1,9 @@
+require 'arel/engines/sql/relations/utilities/compound'
+require 'arel/engines/sql/relations/utilities/recursion'
+require 'arel/engines/sql/relations/utilities/externalization'
+require 'arel/engines/sql/relations/utilities/nil'
+require 'arel/engines/sql/relations/relation'
+require 'arel/engines/sql/relations/table'
+require 'arel/engines/sql/relations/operations/join'
+require 'arel/engines/sql/relations/operations/alias'
+require 'arel/engines/sql/relations/writes'
diff --git a/lib/arel/engines/sql/relations/operations/alias.rb b/lib/arel/engines/sql/relations/operations/alias.rb
new file mode 100644
index 0000000000..9b6a484463
--- /dev/null
+++ b/lib/arel/engines/sql/relations/operations/alias.rb
@@ -0,0 +1,5 @@
+module Arel
+  class Alias < Compound
+    include Recursion::BaseCase
+  end
+end
diff --git a/lib/arel/engines/sql/relations/operations/join.rb b/lib/arel/engines/sql/relations/operations/join.rb
new file mode 100644
index 0000000000..7c5e13510a
--- /dev/null
+++ b/lib/arel/engines/sql/relations/operations/join.rb
@@ -0,0 +1,33 @@
+module Arel
+  class Join < Relation
+    def table_sql(formatter = Sql::TableReference.new(self))
+      relation1.externalize.table_sql(formatter)
+    end
+
+    def joins(environment, formatter = Sql::TableReference.new(environment))
+      @joins ||= begin
+        this_join = [
+          join_sql,
+          relation2.externalize.table_sql(formatter),
+          ("ON" unless predicates.blank?),
+          (ons + relation2.externalize.wheres).collect { |p| p.bind(environment).to_sql(Sql::WhereClause.new(environment)) }.join(' AND ')
+        ].compact.join(" ")
+        [relation1.joins(environment), this_join, relation2.joins(environment)].compact.join(" ")
+      end
+    end
+  end
+
+  class InnerJoin < Join
+    def join_sql; "INNER JOIN" end
+  end
+
+  class OuterJoin < Join
+    def join_sql; "LEFT OUTER JOIN" end
+  end
+
+  class StringJoin < Join
+    def joins(_, __ = nil)
+      relation2
+    end
+  end
+end
diff --git a/lib/arel/engines/sql/relations/relation.rb b/lib/arel/engines/sql/relations/relation.rb
new file mode 100644
index 0000000000..4cfb83a601
--- /dev/null
+++ b/lib/arel/engines/sql/relations/relation.rb
@@ -0,0 +1,50 @@
+module Arel
+  class Relation
+    def to_sql(formatter = Sql::SelectStatement.new(self))
+      formatter.select select_sql, self
+    end
+
+    def select_sql
+      build_query \
+        "SELECT     #{select_clauses.join(', ')}",
+        "FROM       #{table_sql(Sql::TableReference.new(self))}",
+        (joins(self)                                   unless joins(self).blank? ),
+        ("WHERE     #{where_clauses.join("\n\tAND ")}" unless wheres.blank?      ),
+        ("GROUP BY  #{group_clauses.join(', ')}"       unless groupings.blank?   ),
+        ("ORDER BY  #{order_clauses.join(', ')}"       unless orders.blank?      ),
+        ("LIMIT     #{taken}"                          unless taken.blank?       ),
+        ("OFFSET    #{skipped}"                        unless skipped.blank?     )
+    end
+
+    def inclusion_predicate_sql
+      "IN"
+    end
+
+    def christener
+      @christener ||= Sql::Christener.new
+    end
+
+  protected
+
+    def build_query(*parts)
+      parts.compact.join("\n")
+    end
+
+    def select_clauses
+      attributes.collect { |a| a.to_sql(Sql::SelectClause.new(self)) }
+    end
+
+    def where_clauses
+      wheres.collect { |w| w.to_sql(Sql::WhereClause.new(self)) }
+    end
+
+    def group_clauses
+      groupings.collect { |g| g.to_sql(Sql::GroupClause.new(self)) }
+    end
+
+    def order_clauses
+      orders.collect { |o| o.to_sql(Sql::OrderClause.new(self)) }
+    end
+
+  end
+end
diff --git a/lib/arel/engines/sql/relations/table.rb b/lib/arel/engines/sql/relations/table.rb
new file mode 100644
index 0000000000..dd22f44226
--- /dev/null
+++ b/lib/arel/engines/sql/relations/table.rb
@@ -0,0 +1,52 @@
+module Arel
+  class Table < Relation
+    include Recursion::BaseCase
+
+    cattr_accessor :engine
+    attr_reader :name, :engine
+
+    def initialize(name, engine = Table.engine)
+      @name, @engine = name.to_s, engine
+    end
+
+    def attributes
+      @attributes ||= columns.collect do |column|
+        Attribute.new(self, column.name.to_sym)
+      end
+    end
+
+    def eql?(other)
+      self == other
+    end
+
+    def hash
+      @hash ||= :name.hash
+    end
+
+    def format(attribute, value)
+      attribute.column.type_cast(value)
+    end
+
+    def column_for(attribute)
+      has_attribute?(attribute) and columns.detect { |c| c.name == attribute.name.to_s }
+    end
+
+    def columns
+      @columns ||= engine.columns(name, "#{name} Columns")
+    end
+
+    def reset
+      @attributes = @columns = nil
+    end
+
+    def ==(other)
+      Table      === other and
+      name       ==  other.name
+    end
+  end
+end
+
+def Table(name, engine = Arel::Table.engine)
+  Arel::Table.new(name, engine)
+end
+
diff --git a/lib/arel/engines/sql/relations/utilities/compound.rb b/lib/arel/engines/sql/relations/utilities/compound.rb
new file mode 100644
index 0000000000..f8ce4033fd
--- /dev/null
+++ b/lib/arel/engines/sql/relations/utilities/compound.rb
@@ -0,0 +1,10 @@
+module Arel
+  class Compound < Relation
+    delegate :table, :table_sql, :to => :relation
+
+    def build_query(*parts)
+      parts.compact.join("\n")
+    end
+  end
+end
+
diff --git a/lib/arel/engines/sql/relations/utilities/externalization.rb b/lib/arel/engines/sql/relations/utilities/externalization.rb
new file mode 100644
index 0000000000..7f937e8423
--- /dev/null
+++ b/lib/arel/engines/sql/relations/utilities/externalization.rb
@@ -0,0 +1,14 @@
+module Arel
+  class Externalization < Compound
+    include Recursion::BaseCase
+
+    def table_sql(formatter = Sql::TableReference.new(relation))
+      formatter.select relation.select_sql, self
+    end
+
+    # REMOVEME
+    def name
+      relation.name + '_external'
+    end
+  end
+end
diff --git a/lib/arel/engines/sql/relations/utilities/nil.rb b/lib/arel/engines/sql/relations/utilities/nil.rb
new file mode 100644
index 0000000000..519ea8acf1
--- /dev/null
+++ b/lib/arel/engines/sql/relations/utilities/nil.rb
@@ -0,0 +1,6 @@
+module Arel
+  class Nil < Relation
+    def table_sql(formatter = nil); '' end
+    def name; '' end
+  end
+end
diff --git a/lib/arel/engines/sql/relations/utilities/recursion.rb b/lib/arel/engines/sql/relations/utilities/recursion.rb
new file mode 100644
index 0000000000..84a526f57c
--- /dev/null
+++ b/lib/arel/engines/sql/relations/utilities/recursion.rb
@@ -0,0 +1,13 @@
+module Arel
+  module Recursion
+    module BaseCase
+      def table
+        self
+      end
+
+      def table_sql(formatter = Sql::TableReference.new(self))
+        formatter.table self
+      end
+    end
+  end
+end
diff --git a/lib/arel/engines/sql/relations/writes.rb b/lib/arel/engines/sql/relations/writes.rb
new file mode 100644
index 0000000000..f1a9bfd2ac
--- /dev/null
+++ b/lib/arel/engines/sql/relations/writes.rb
@@ -0,0 +1,39 @@
+module Arel
+  class Deletion < Compound
+    def to_sql(formatter = nil)
+      build_query \
+        "DELETE",
+        "FROM #{table_sql}",
+        ("WHERE #{wheres.collect(&:to_sql).join('\n\tAND ')}" unless wheres.blank? ),
+        ("LIMIT #{taken}"                                     unless taken.blank?  )
+    end
+  end
+
+  class Insert < Compound
+    def to_sql(formatter = nil)
+      build_query \
+        "INSERT",
+        "INTO #{table_sql}",
+        "(#{record.keys.collect { |key| engine.quote_column_name(key.name) }.join(', ')})",
+        "VALUES (#{record.collect { |key, value| key.format(value) }.join(', ')})"
+    end
+  end
+
+  class Update < Compound
+    def to_sql(formatter = nil)
+      build_query \
+        "UPDATE #{table_sql} SET",
+        assignment_sql,
+        ("WHERE #{wheres.collect(&:to_sql).join('\n\tAND ')}"  unless wheres.blank? ),
+        ("LIMIT #{taken}"                                      unless taken.blank?  )
+    end
+
+  protected
+
+    def assignment_sql
+      assignments.collect do |attribute, value|
+        "#{engine.quote_column_name(attribute.name)} = #{attribute.format(value)}"
+      end.join(",\n")
+    end
+  end
+end
diff --git a/lib/arel/session.rb b/lib/arel/session.rb
new file mode 100644
index 0000000000..921ad0a7ac
--- /dev/null
+++ b/lib/arel/session.rb
@@ -0,0 +1,48 @@
+module Arel
+  class Session
+    class << self
+      attr_accessor :instance
+      alias_method :manufacture, :new
+
+      def start
+        if @started
+          yield
+        else
+          begin
+            @started = true
+            @instance = manufacture
+            metaclass.send :alias_method, :new, :instance
+            yield
+          ensure
+            metaclass.send :alias_method, :new, :manufacture
+            @started = false
+          end
+        end
+      end
+    end
+
+    module CRUD
+      def create(insert)
+        insert.call
+        insert
+      end
+
+      def read(select)
+        (@read ||= Hash.new do |hash, select|
+          hash[select] = select.call
+        end)[select]
+      end
+
+      def update(update)
+        update.call
+        update
+      end
+
+      def delete(delete)
+        delete.call
+        delete
+      end
+    end
+    include CRUD
+  end
+end