1 files changed, 36 insertions, 10 deletions
diff --git a/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb b/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb
index 3f90d61e2d..378fc79949 100644
--- a/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb
+++ b/activerecord/lib/active_record/associations/has_and_belongs_to_many_association.rb
@@ -38,15 +38,42 @@ module ActiveRecord
         self
       end
 
-      def find(association_id = nil, &block)
-        if block_given? || @options[:finder_sql]
-          load_collection
-          @collection.find(&block)
+      def find_first
+        load_collection.first
+      end
+
+      def find(*args)
+        # Return an Array if multiple ids are given.
+        expects_array = args.first.kind_of?(Array)
+
+        ids = args.flatten.compact.uniq
+
+        # If no block is given, raise RecordNotFound.
+        if ids.empty?
+          raise RecordNotFound, "Couldn't find #{@association_class.name} without an ID#{conditions}"
+
+        # If using a custom finder_sql, scan the entire collection.
+        elsif @options[:finder_sql]
+          if ids.size == 1
+            id = ids.first
+            record = load_collection.detect { |record| id == record.id }
+            expects_array? ? [record] : record
+          else
+            load_collection.select { |record| ids.include?(record.id) }
+          end
+
+        # Otherwise, construct a query.
         else
-          if loaded?
-            find_all { |record| record.id == association_id.to_i }.first
+          ids_list = ids.map { |id| @owner.send(:quote, id) }.join(',')
+          records = find_all_records(@finder_sql.sub(/ORDER BY/, "AND j.#{@association_foreign_key} IN (#{ids_list}) ORDER BY"))
+          if records.size == ids.size
+            if ids.size == 1 and !expects_array
+              records.first
+            else
+              records
+            end
           else
-            find_all_records(@finder_sql.sub(/ORDER BY/, "AND j.#{@association_foreign_key} = #{@owner.send(:quote, association_id)} ORDER BY")).first
+            raise RecordNotFound, "Couldn't find #{@association_class.name} with ID in (#{ids_list})"
           end
         end
       end
@@ -70,10 +97,9 @@ module ActiveRecord
           records = @association_class.find_by_sql(sql)
           @options[:uniq] ? uniq(records) : records
         end
-            
+
         def count_records
-          load_collection
-          @collection.size
+          load_collection.size
         end
 
         def insert_record(record)