14 files changed, 412 insertions, 0 deletions
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