PERF: Active Record #pluck is twice faster

PERF: SqlBuilder bypasses AR converters and uses PG directly

lib/sql_builder.rb

@@ -36,9 +36,9 @@ class SqlBuilder
       when :where, :where2
         joined = "WHERE " << v.map{|c| "(" << c << ")" }.join(" AND ")
       when :join
-        joined = v.map{|v| "JOIN " << v }.join("\n")
+        joined = v.map{|item| "JOIN " << item }.join("\n")
       when :left_join
-        joined = v.map{|v| "LEFT JOIN " << v }.join("\n")
+        joined = v.map{|item| "LEFT JOIN " << item }.join("\n")
       when :limit
         joined = "LIMIT " << v.last.to_s
       when :offset
@@ -69,46 +69,50 @@ class SqlBuilder
     end
   end
 
-  #AS reloads this on tests
-  remove_const :FTYPE_MAP if defined? FTYPE_MAP
-
-  if Rails.version >= "4.2.0"
-    FTYPE_MAP = {
-      23 => ActiveRecord::Type::Integer.new,
-      1114 => ActiveRecord::Type::DateTime.new,
-      16 => ActiveRecord::Type::Boolean.new
-    }
-  else
-    FTYPE_MAP = {
-      23 => :value_to_integer,
-      1114 => :string_to_time,
-      16 => :value_to_boolean
-    }
-  end
-
   def self.map_exec(klass, sql, args = {})
     self.new(sql).map_exec(klass, args)
   end
 
+  class RailsDateTimeDecoder < PG::SimpleDecoder
+    def decode(string, tuple=nil, field=nil)
+      if Rails.version >= "4.2.0"
+        @caster ||= ActiveRecord::Type::DateTime.new
+        @caster.type_cast_from_database(string)
+      else
+        ActiveRecord::ConnectionAdapters::Column.string_to_time string
+      end
+    end
+  end
+
+
+  class ActiveRecordTypeMap < PG::BasicTypeMapForResults
+    def initialize(connection)
+      super(connection)
+      rm_coder 0, 1114
+      add_coder RailsDateTimeDecoder.new(name: "timestamp", oid: 1114, format: 0)
+      # we don't need deprecations
+     	self.default_type_map = PG::TypeMapInRuby.new
+    end
+  end
+
+  def self.pg_type_map
+    conn = ActiveRecord::Base.connection.raw_connection
+    @typemap ||= ActiveRecordTypeMap.new(conn)
+  end
+
   def map_exec(klass = OpenStruct, args = {})
     results = exec(args)
+    results.type_map = SqlBuilder.pg_type_map
 
     setters = results.fields.each_with_index.map do |f, index|
-      [(f.dup << "=").to_sym, FTYPE_MAP[results.ftype(index)]]
+      f.dup << "="
     end
+
     values = results.values
     values.map! do |row|
       mapped = klass.new
-      setters.each_with_index do |mapper, index|
-        translated = row[index]
-        if mapper[1] && !translated.nil?
-          if Rails.version >= "4.2.0"
-            translated = mapper[1].type_cast_from_database(translated)
-          else
-            translated = ActiveRecord::ConnectionAdapters::Column.send mapper[1], translated
-          end
-        end
-        mapped.send mapper[0], translated
+      setters.each_with_index do |name, index|
+        mapped.send name, row[index]
       end
       mapped
     end