1 files changed, 33 insertions, 12 deletions

diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index 52531a3520..80ae38b3fb 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -96,11 +96,31 @@ module ActiveRecord
       end
 
       def first(*args)
-        first_or_last(:first, *args)
+        first_nth_or_last(:first, *args)
+      end
+
+      def second(*args)
+        first_nth_or_last(:second, *args)
+      end
+
+      def third(*args)
+        first_nth_or_last(:third, *args)
+      end
+
+      def fourth(*args)
+        first_nth_or_last(:fourth, *args)
+      end
+
+      def fifth(*args)
+        first_nth_or_last(:fifth, *args)
+      end
+
+      def forty_two(*args)
+        first_nth_or_last(:forty_two, *args)
       end
 
       def last(*args)
-        first_or_last(:last, *args)
+        first_nth_or_last(:last, *args)
       end
 
       def build(attributes = {}, &block)
@@ -125,9 +145,8 @@ module ActiveRecord
       # be chained. Since << flattens its argument list and inserts each record,
       # +push+ and +concat+ behave identically.
       def concat(*records)
-        load_target if owner.new_record?
-
         if owner.new_record?
+          load_target
           concat_records(records)
         else
           transaction { concat_records(records) }
@@ -229,7 +248,7 @@ module ActiveRecord
         dependent = _options[:dependent] || options[:dependent]
 
         if records.first == :all
-          if loaded? || dependent == :destroy
+          if (loaded? || dependent == :destroy) && dependent != :delete_all
             delete_or_destroy(load_target, dependent)
           else
             delete_records(:all, dependent)
@@ -339,7 +358,9 @@ module ActiveRecord
         if owner.new_record?
           replace_records(other_array, original_target)
         else
-          transaction { replace_records(other_array, original_target) }
+          if other_array != original_target
+            transaction { replace_records(other_array, original_target) }
+          end
         end
       end
 
@@ -348,7 +369,7 @@ module ActiveRecord
           if record.new_record?
             include_in_memory?(record)
           else
-            loaded? ? target.include?(record) : scope.exists?(record)
+            loaded? ? target.include?(record) : scope.exists?(record.id)
           end
         else
           false
@@ -493,13 +514,13 @@ module ActiveRecord
           target
         end
 
-        def concat_records(records)
+        def concat_records(records, should_raise = false)
           result = true
 
           records.flatten.each do |record|
             raise_on_type_mismatch!(record)
             add_to_target(record) do |rec|
-              result &&= insert_record(rec) unless owner.new_record?
+              result &&= insert_record(rec, true, should_raise) unless owner.new_record?
             end
           end
 
@@ -526,7 +547,7 @@ module ActiveRecord
         #   * target already loaded
         #   * owner is new record
         #   * target contains new or changed record(s)
-        def fetch_first_or_last_using_find?(args)
+        def fetch_first_nth_or_last_using_find?(args)
           if args.first.is_a?(Hash)
             true
           else
@@ -564,10 +585,10 @@ module ActiveRecord
         end
 
         # Fetches the first/last using SQL if possible, otherwise from the target array.
-        def first_or_last(type, *args)
+        def first_nth_or_last(type, *args)
           args.shift if args.first.is_a?(Hash) && args.first.empty?
 
-          collection = fetch_first_or_last_using_find?(args) ? scope : load_target
+          collection = fetch_first_nth_or_last_using_find?(args) ? scope : load_target
           collection.send(type, *args).tap do |record|
             set_inverse_instance record if record.is_a? ActiveRecord::Base
           end