Replace map.flatten with flat_map in activerecord

activerecord/lib/active_record/associations.rb

@@ -530,8 +530,8 @@ def association_instance_set(name, association)
     #   end
     #
     #   @firm = Firm.first
-    #   @firm.clients.collect { |c| c.invoices }.flatten # select all invoices for all clients of the firm
-    #   @firm.invoices                                   # selects all invoices by going through the Client join model
+    #   @firm.clients.flat_map { |c| c.invoices } # select all invoices for all clients of the firm
+    #   @firm.invoices                            # selects all invoices by going through the Client join model
     #
     # Similarly you can go through a +has_one+ association on the join model:
     #

activerecord/lib/active_record/associations/preloader/through_association.rb

@@ -23,7 +23,7 @@ def associated_records_by_owner(preloader)
 
           reset_association owners, through_reflection.name
 
-          middle_records = through_records.map { |(_,rec)| rec }.flatten
+          middle_records = through_records.flat_map { |(_,rec)| rec }
 
           preloaders = preloader.preload(middle_records,
                                          source_reflection.name,

activerecord/lib/active_record/connection_adapters/abstract_mysql_adapter.rb

@@ -459,7 +459,7 @@ def create_table(table_name, options = {}) #:nodoc:
       end
 
       def bulk_change_table(table_name, operations) #:nodoc:
-        sqls = operations.map do |command, args|
+        sqls = operations.flat_map do |command, args|
           table, arguments = args.shift, args
           method = :"#{command}_sql"
 
@@ -468,7 +468,7 @@ def bulk_change_table(table_name, operations) #:nodoc:
           else
             raise "Unknown method called : #{method}(#{arguments.inspect})"
           end
-        end.flatten.join(", ")
+        end.join(", ")
 
         execute("ALTER TABLE #{quote_table_name(table_name)} #{sqls}")
       end

activerecord/test/cases/associations/callbacks_test.rb

@@ -159,7 +159,7 @@ def test_has_and_belongs_to_many_remove_callback_on_clear
       activerecord.reload
       assert activerecord.developers_with_callbacks.size == 2
     end
-    log_array = activerecord.developers_with_callbacks.collect {|d| ["before_removing#{d.id}","after_removing#{d.id}"]}.flatten.sort
+    log_array = activerecord.developers_with_callbacks.flat_map {|d| ["before_removing#{d.id}","after_removing#{d.id}"]}.sort
     assert activerecord.developers_with_callbacks.clear
     assert_equal log_array, activerecord.developers_log.sort
   end

activerecord/test/cases/autosave_association_test.rb

@@ -76,9 +76,9 @@ def assert_no_difference_when_adding_callbacks_twice_for(model, association_name
   end
 
   def callbacks_for_model(model)
-    model.instance_variables.grep(/_callbacks$/).map do |ivar|
+    model.instance_variables.grep(/_callbacks$/).flat_map do |ivar|
       model.instance_variable_get(ivar)
-    end.flatten
+    end
   end
 end