Revert "Improve performance of AR object instantiation"

This reverts commit 8fee923888192a658d8823b31e77ed0683dfd665.

Conflicts:
	activerecord/lib/active_record/attribute_set/builder.rb

This solution sucks, and is hard to actually apply across the board.
Going to try other solutions

5 files changed, 11 insertions, 61 deletions

diff --git a/activerecord/lib/active_record/attribute_set/builder.rb b/activerecord/lib/active_record/attribute_set/builder.rb
index 0a62c68bfb..d4a787f2fe 100644
--- a/activerecord/lib/active_record/attribute_set/builder.rb
+++ b/activerecord/lib/active_record/attribute_set/builder.rb
@@ -8,33 +8,18 @@ module ActiveRecord
       end
 
       def build_from_database(values = {}, additional_types = {})
-        build_from_database_pairs(values.keys, values.values, additional_types)
-      end
-
-      def build_from_database_pairs(columns, values, additional_types)
-        attributes = build_attributes_from_values(columns, values, additional_types)
+        attributes = build_attributes_from_values(values, additional_types)
         add_uninitialized_attributes(attributes)
         AttributeSet.new(attributes)
       end
 
       private
 
-      def build_attributes_from_values(columns, values, additional_types)
-        # We are performing manual iteration here as this method is a performance
-        # hotspot
-        hash = {}
-        index = 0
-        length = columns.length
-
-        while index < length
-          name = columns[index]
-          value = values[index]
+      def build_attributes_from_values(values, additional_types)
+        values.each_with_object({}) do |(name, value), hash|
           type = additional_types.fetch(name, types[name])
           hash[name] = Attribute.from_database(name, value, type)
-          index += 1
         end
-
-        hash
       end
 
       def add_uninitialized_attributes(attributes)
diff --git a/activerecord/lib/active_record/inheritance.rb b/activerecord/lib/active_record/inheritance.rb
index 4aad3217cb..f58145ab05 100644
--- a/activerecord/lib/active_record/inheritance.rb
+++ b/activerecord/lib/active_record/inheritance.rb
@@ -165,19 +165,15 @@ module ActiveRecord
       # record instance. For single-table inheritance, we check the record
       # for a +type+ column and return the corresponding class.
       def discriminate_class_for_record(record)
-        discriminate_class_for_value(record[inheritance_column])
-      end
-
-      def discriminate_class_for_value(value)
-        if using_single_table_inheritance?(value)
-          find_sti_class(value)
+        if using_single_table_inheritance?(record)
+          find_sti_class(record[inheritance_column])
         else
           super
         end
       end
 
-      def using_single_table_inheritance?(value)
-        value.present? && columns_hash.include?(inheritance_column)
+      def using_single_table_inheritance?(record)
+        record[inheritance_column].present? && columns_hash.include?(inheritance_column)
       end
 
       def find_sti_class(type_name)
diff --git a/activerecord/lib/active_record/persistence.rb b/activerecord/lib/active_record/persistence.rb
index 06c8bceb30..507faf2879 100644
--- a/activerecord/lib/active_record/persistence.rb
+++ b/activerecord/lib/active_record/persistence.rb
@@ -65,41 +65,19 @@ module ActiveRecord
       # how this "single-table" inheritance mapping is implemented.
       def instantiate(attributes, column_types = {})
         klass = discriminate_class_for_record(attributes)
-        klass.instantiate_pairs(attributes.keys, attributes.values, column_types)
-      end
-
-      def instantiate_pairs(columns, values, column_types = {}) # :nodoc:
-        attributes = attributes_builder.build_from_database_pairs(columns, values, column_types)
-        allocate.init_with('attributes' => attributes, 'new_record' => false)
-      end
-
-      def instantiate_result_set(result_set, column_types = {}) # :nodoc:
-        inheritance_column_index = inheritance_column && result_set.columns.find_index(inheritance_column)
-
-        result_set.each_pair.map do |columns, values|
-          inheritance_value = inheritance_column_index && values[inheritance_column_index]
-          klass = discriminate_class_for_value(inheritance_value)
-          klass.instantiate_pairs(columns, values, column_types)
-        end
+        attributes = klass.attributes_builder.build_from_database(attributes, column_types)
+        klass.allocate.init_with('attributes' => attributes, 'new_record' => false)
       end
 
       private
         # Called by +instantiate+ to decide which class to use for a new
         # record instance.
         #
-        # See +ActiveRecord::Inheritance#discriminate_class_for_value+ for
+        # See +ActiveRecord::Inheritance#discriminate_class_for_record+ for
         # the single-table inheritance discriminator.
-        def discriminate_class_for_value(*)
-          self
-        end
-
         def discriminate_class_for_record(record)
           self
         end
-
-        def inheritance_column
-          nil
-        end
     end
 
     # Returns true if this object hasn't been saved yet -- that is, a record
diff --git a/activerecord/lib/active_record/querying.rb b/activerecord/lib/active_record/querying.rb
index 9d4df81b07..e8de4db3a7 100644
--- a/activerecord/lib/active_record/querying.rb
+++ b/activerecord/lib/active_record/querying.rb
@@ -47,7 +47,7 @@ module ActiveRecord
       }
 
       message_bus.instrument('instantiation.active_record', payload) do
-        instantiate_result_set(result_set, column_types)
+        result_set.map { |record| instantiate(record, column_types) }
       end
     end
 
diff --git a/activerecord/lib/active_record/result.rb b/activerecord/lib/active_record/result.rb
index c84ad586e2..3a3e65ef32 100644
--- a/activerecord/lib/active_record/result.rb
+++ b/activerecord/lib/active_record/result.rb
@@ -54,15 +54,6 @@ module ActiveRecord
       end
     end
 
-    def each_pair
-      return to_enum(__method__) unless block_given?
-
-      columns = @columns.map { |c| c.dup.freeze }
-      @rows.each do |row|
-        yield columns, row
-      end
-    end
-
     def to_hash
       hash_rows
     end