1 files changed, 150 insertions, 0 deletions
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