diff --git a/activerecord/lib/active_record/associations/collection_association.rb b/activerecord/lib/active_record/associations/collection_association.rb
index 48628230c7..caf4e612f9 100644
--- a/activerecord/lib/active_record/associations/collection_association.rb
+++ b/activerecord/lib/active_record/associations/collection_association.rb
@@ -194,7 +194,7 @@ def delete_all(dependent = nil)
                       options[:dependent]
                     end
 
-        delete_records(:all, dependent).tap do
+        delete_or_nullify_all_records(dependent).tap do
           reset
           loaded!
         end
diff --git a/activerecord/lib/active_record/associations/has_many_association.rb b/activerecord/lib/active_record/associations/has_many_association.rb
index aac85a36c8..f5e911c739 100644
--- a/activerecord/lib/active_record/associations/has_many_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_association.rb
@@ -105,23 +105,27 @@ def inverse_updates_counter_cache?(reflection = reflection())
           }
         end
 
+        def delete_count(method, scope)
+          if method == :delete_all
+            scope.delete_all
+          else
+            scope.update_all(reflection.foreign_key => nil)
+          end
+        end
+
+        def delete_or_nullify_all_records(method)
+          count = delete_count(method, self.scope)
+          update_counter(-count)
+        end
+
         # Deletes the records according to the <tt>:dependent</tt> option.
         def delete_records(records, method)
           if method == :destroy
             records.each(&:destroy!)
             update_counter(-records.length) unless inverse_updates_counter_cache?
           else
-            if records == :all || !reflection.klass.primary_key
-              scope = self.scope
-            else
-              scope = self.scope.where(reflection.klass.primary_key => records)
-            end
-
-            if method == :delete_all
-              update_counter(-scope.delete_all)
-            else
-              update_counter(-scope.update_all(reflection.foreign_key => nil))
-            end
+            scope = self.scope.where(reflection.klass.primary_key => records)
+            update_counter(-delete_count(method, scope))
           end
         end
 
diff --git a/activerecord/lib/active_record/associations/has_many_through_association.rb b/activerecord/lib/active_record/associations/has_many_through_association.rb
index aeb77e2753..35ad512537 100644
--- a/activerecord/lib/active_record/associations/has_many_through_association.rb
+++ b/activerecord/lib/active_record/associations/has_many_through_association.rb
@@ -130,13 +130,13 @@ def update_through_counter?(method)
           end
         end
 
+        def delete_or_nullify_all_records(method)
+          delete_records(load_target, method)
+        end
+
         def delete_records(records, method)
           ensure_not_nested
 
-          # This is unoptimised; it will load all the target records
-          # even when we just want to delete everything.
-          records = load_target if records == :all
-
           scope = through_association.scope
           scope.where! construct_join_attributes(*records)