Create an Arel::Header class representing a relation's attributes

7 files changed, 99 insertions, 27 deletions

diff --git a/lib/arel/algebra/attributes/attribute.rb b/lib/arel/algebra/attributes/attribute.rb
index 331f218463..afcbdd8301 100644
--- a/lib/arel/algebra/attributes/attribute.rb
+++ b/lib/arel/algebra/attributes/attribute.rb
@@ -29,7 +29,7 @@ module Arel
       end
 
       def hash
-        @hash ||= history.size + name.hash + relation.hash
+        @hash ||= name.hash + root.relation.hash
       end
 
       def as(aliaz = nil)
diff --git a/lib/arel/algebra/header.rb b/lib/arel/algebra/header.rb
new file mode 100644
index 0000000000..ec45488dbf
--- /dev/null
+++ b/lib/arel/algebra/header.rb
@@ -0,0 +1,71 @@
+module Arel
+  class Header
+    include Enumerable
+
+    def initialize(attrs = [])
+      @attributes = attrs.to_ary
+      @names = Hash.new do |h,k|
+        h[k] = @attributes.detect { |a| a.named?(k) }
+      end
+    end
+
+    def each(&block)
+      to_ary.each(&block)
+      self
+    end
+
+    def [](key)
+      case key
+      when String, Symbol then find_by_name(key)
+      when Attribute      then find_by_attribute(key)
+      end
+    end
+
+    def ==(other)
+      to_set == other.to_set
+    end
+
+    def union(other)
+      new(to_ary | other)
+    end
+
+    alias | union
+
+    def to_ary
+      @attributes
+    end
+
+    def bind(relation)
+      Header.new(map { |a| a.bind(relation) })
+    end
+
+    # TMP
+    def index(i)
+      to_ary.index(i)
+    end
+
+  private
+
+    def new(attrs)
+      self.class.new(attrs)
+    end
+
+    def matching(attribute)
+      # (@matching_attributes ||= attributes.inject({}) do |hash, a|
+      #   (hash[a.is_a?(Value) ? a.value : a.root] ||= []) << a
+      #   hash
+      # end)[attribute.root] || []
+      select { |a| !a.is_a?(Value) && a.root == attribute.root }
+    end
+
+    def find_by_name(name)
+      @names[name.to_sym]
+    end
+
+    def find_by_attribute(attr)
+      matching(attr).max do |a, b|
+        (a.original_attribute / attr) <=> (b.original_attribute / attr)
+      end
+    end
+  end
+end
\ No newline at end of file
diff --git a/lib/arel/algebra/relations/operations/join.rb b/lib/arel/algebra/relations/operations/join.rb
index 300cd31bcd..21bcfaa62d 100644
--- a/lib/arel/algebra/relations/operations/join.rb
+++ b/lib/arel/algebra/relations/operations/join.rb
@@ -19,8 +19,7 @@ module Arel
     end
 
     def attributes
-      @attributes ||= (relation1.externalize.attributes +
-        relation2.externalize.attributes).collect { |a| a.bind(self) }
+      @attributes ||= (relation1.externalize.attributes | relation2.externalize.attributes).bind(self)
     end
 
     def wheres
diff --git a/lib/arel/algebra/relations/operations/project.rb b/lib/arel/algebra/relations/operations/project.rb
index a1140e91c1..49d0e1be36 100644
--- a/lib/arel/algebra/relations/operations/project.rb
+++ b/lib/arel/algebra/relations/operations/project.rb
@@ -10,7 +10,7 @@ module Arel
     end
 
     def attributes
-      @attributes ||= projections.collect { |p| p.bind(self) }
+      @attributes ||= Header.new(projections).bind(self)
     end
 
     def externalizable?
diff --git a/lib/arel/algebra/relations/relation.rb b/lib/arel/algebra/relations/relation.rb
index 1c1ded15c9..ef2108dcaa 100644
--- a/lib/arel/algebra/relations/relation.rb
+++ b/lib/arel/algebra/relations/relation.rb
@@ -84,16 +84,14 @@ module Arel
 
     module AttributeAccessable
       def [](index)
-        @cached_attributes ||= {}
-        @cached_attributes[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] }
+        attr = attributes[index]
+
+        # Handles a strange ActiveRecord case
+        if !attr && (index.is_a?(String) || index.is_a?(Symbol))
+          attr = Attribute.new(self, index)
         end
+
+        attr
       end
 
       def find_attribute_matching_name(name)
@@ -127,18 +125,18 @@ module Arel
     include AttributeAccessable
 
     module DefaultOperations
-      def attributes;             []  end
-      def projections;            []  end
-      def wheres;                 []  end
-      def orders;                 []  end
-      def inserts;                []  end
-      def groupings;              []  end
-      def havings;                []  end
-      def joins(formatter = nil); nil end # FIXME
-      def taken;                  nil end
-      def skipped;                nil end
-      def sources;                []  end
-      def locked;                 []  end
+      def attributes;             Header.new  end
+      def projections;            []          end
+      def wheres;                 []          end
+      def orders;                 []          end
+      def inserts;                []          end
+      def groupings;              []          end
+      def havings;                []          end
+      def joins(formatter = nil); nil         end # FIXME
+      def taken;                  nil         end
+      def skipped;                nil         end
+      def sources;                []          end
+      def locked;                 []          end
     end
     include DefaultOperations
   end
diff --git a/lib/arel/algebra/relations/utilities/compound.rb b/lib/arel/algebra/relations/utilities/compound.rb
index 7039b82575..416717310c 100644
--- a/lib/arel/algebra/relations/utilities/compound.rb
+++ b/lib/arel/algebra/relations/utilities/compound.rb
@@ -13,7 +13,7 @@ module Arel
       @requires
     end
 
-    [:attributes, :wheres, :groupings, :orders, :havings, :projections].each do |operation_name|
+    [:wheres, :groupings, :orders, :havings, :projections].each do |operation_name|
       class_eval <<-OPERATION, __FILE__, __LINE__
         def #{operation_name}
           @#{operation_name} ||= relation.#{operation_name}.collect { |o| o.bind(self) }
@@ -21,6 +21,10 @@ module Arel
       OPERATION
     end
 
+    def attributes
+      @attributes ||= relation.attributes.bind(self)
+    end
+
     def hash
       @hash ||= :relation.hash
     end
diff --git a/lib/arel/algebra/relations/utilities/externalization.rb b/lib/arel/algebra/relations/utilities/externalization.rb
index 795a3919f2..edd8f99221 100644
--- a/lib/arel/algebra/relations/utilities/externalization.rb
+++ b/lib/arel/algebra/relations/utilities/externalization.rb
@@ -8,7 +8,7 @@ module Arel
     end
 
     def attributes
-      @attributes ||= relation.attributes.collect { |a| a.to_attribute(self) }
+      @attributes ||= Header.new(relation.attributes.map { |a| a.to_attribute(self) })
     end
   end