create_fixtures

# File activerecord/lib/active_record/fixtures.rb, line 511
    def self.create_fixtures(fixtures_directory, fixture_set_names, class_names = {}, config = ActiveRecord::Base)
      fixture_set_names = Array(fixture_set_names).map(&:to_s)
      class_names = ClassCache.new class_names, config

      # FIXME: Apparently JK uses this.
      connection = block_given? ? yield : ActiveRecord::Base.connection

      files_to_read = fixture_set_names.reject { |fs_name|
        fixture_is_cached?(connection, fs_name)
      }

      unless files_to_read.empty?
        connection.disable_referential_integrity do
          fixtures_map = {}

          fixture_sets = files_to_read.map do |fs_name|
            klass = class_names[fs_name]
            conn = klass ? klass.connection : connection
            fixtures_map[fs_name] = new( # ActiveRecord::FixtureSet.new
              conn,
              fs_name,
              klass,
              ::File.join(fixtures_directory, fs_name))
          end

          update_all_loaded_fixtures fixtures_map

          connection.transaction(requires_new: true) do
            deleted_tables = Hash.new { |h, k| h[k] = Set.new }
            fixture_sets.each do |fs|
              conn = fs.model_class.respond_to?(:connection) ? fs.model_class.connection : connection
              table_rows = fs.table_rows

              table_rows.each_key do |table|
                unless deleted_tables[conn].include? table
                  conn.delete "DELETE FROM #{conn.quote_table_name(table)}", "Fixture Delete"
                end
                deleted_tables[conn] << table
              end

              table_rows.each do |fixture_set_name, rows|
                rows.each do |row|
                  conn.insert_fixture(row, fixture_set_name)
                end
              end

              # Cap primary key sequences to max(pk).
              if conn.respond_to?(:reset_pk_sequence!)
                conn.reset_pk_sequence!(fs.table_name)
              end
            end
          end

          cache_fixtures(connection, fixtures_map)
        end
      end
      cached_fixtures(connection, fixture_set_names)
    end