1 files changed, 141 insertions, 0 deletions
diff --git a/lib/arel/primitives/attribute.rb b/lib/arel/primitives/attribute.rb
new file mode 100644
index 0000000000..280fc9f439
--- /dev/null
+++ b/lib/arel/primitives/attribute.rb
@@ -0,0 +1,141 @@
+module Arel
+  class Attribute
+    attr_reader :relation, :name, :alias, :ancestor
+    delegate :engine, :to => :relation
+
+    def initialize(relation, name, options = {})
+      @relation, @name, @alias, @ancestor = relation, name, options[:alias], options[:ancestor]
+    end
+    
+    def alias_or_name
+      @alias || name
+    end
+    
+    def aggregation?
+      false
+    end
+
+    module Transformations
+      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
+        self
+      end
+    end
+    include Transformations
+    
+    def qualified_name
+      "#{prefix}.#{name}"
+    end
+    
+    def column
+      relation.column_for(self)
+    end
+
+    def ==(other)
+      self.class  == other.class     and
+      relation    == other.relation  and
+      name        == other.name      and
+      @alias      == other.alias     and
+      ancestor    == other.ancestor
+    end
+    
+    module Congruence
+      def self.included(klass)
+        klass.hash_on :name
+      end
+      
+      def history
+        [self] + (ancestor ? [ancestor, ancestor.history].flatten : [])
+      end
+      
+      def =~(other)
+        !(history & other.history).empty?
+      end
+      
+      def %(other)
+        if other then (history - other.history) + (other.history - history)
+        else history
+        end
+      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
+        Expression.new(self, "COUNT")
+      end
+      
+      def sum
+        Expression.new(self, "SUM")
+      end
+      
+      def maximum
+        Expression.new(self, "MAX")
+      end
+      
+      def minimum
+        Expression.new(self, "MIN")
+      end
+      
+      def average
+        Expression.new(self, "AVG")
+      end
+    end
+    include Expressions
+
+    def to_sql(formatter = Sql::WhereCondition.new(engine))
+      formatter.attribute prefix, name, self.alias
+    end
+    
+    def format(object)
+      object.to_sql(formatter)
+    end
+    
+    private
+    def formatter
+      Sql::Attribute.new(self)
+    end
+    
+    def prefix
+      relation.prefix_for(self)
+    end
+  end
+end
+\ No newline at end of file