8 files changed, 153 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