capture the number of rows instantiated for active record (#585)

This is close to telling you the number of rows brought back from the database
It doesn't show pluck results, so just need to keep that in mind.

But it does help you understand why so much memory is being taken up from active
record queries.

lib/mini_profiler/profiling_methods.rb

@@ -17,6 +17,10 @@ def record_sql(query, elapsed_ms, params = nil)
         )
       end
 
+      def report_reader_duration(elapsed_ms, row_count = nil, class_name = nil)
+        current&.current_timer&.report_reader_duration(elapsed_ms, row_count, class_name)
+      end
+
       def start_step(name)
         return unless current
         parent_timer          = current.current_timer

lib/mini_profiler/timer_struct/request.rb

@@ -125,6 +125,12 @@ def move_sql(sql, destination)
           end
         end
 
+        # please call SqlTiming#report_reader_duration instead
+        def report_reader_duration(elapsed_ms, row_count = nil, class_name = nil)
+          last_time = self[:sql_timings]&.last
+          last_time&.report_reader_duration(elapsed_ms, row_count, class_name)
+        end
+
         def add_custom(type, elapsed_ms, page)
           TimerStruct::Custom.new(type, elapsed_ms, page, self).tap do |timer|
             timer[:parent_timing_id] = self[:id]

lib/mini_profiler/timer_struct/sql.rb

@@ -51,12 +51,14 @@ def initialize(query, duration_ms, page, parent, params = nil, skip_backtrace =
           )
         end
 
-        def report_reader_duration(elapsed_ms)
+        def report_reader_duration(elapsed_ms, row_count = nil, class_name = nil)
           return if @reported
           @reported = true
           self[:duration_milliseconds]                += elapsed_ms
           @parent[:sql_timings_duration_milliseconds] += elapsed_ms
           @page[:duration_milliseconds_in_sql]        += elapsed_ms
+          self[:row_count] = self[:row_count].to_i + row_count if row_count
+          self[:class_name] = class_name if class_name
         end
 
         def trim_binds(binds)

lib/mini_profiler_rails/railtie.rb

@@ -114,6 +114,16 @@ def self.initialize!(app)
             Rack::MiniProfiler.binds_to_params(payload[:binds])
           )
         end
+
+        subscribe("instantiation.active_record") do |name, start, finish, id, payload|
+          next if !should_measure?
+
+          Rack::MiniProfiler.report_reader_duration(
+            (finish - start) * 1000,
+            payload[:record_count],
+            payload[:class_name]
+          )
+        end
       end
     end
     @already_initialized = true