Implement limit & offset for ourselves

We know the query will return exactly one row for each entry in the
`ids` array, so we can do all the limit/offset calculations on that
array, in advance.

I also split our new ordered-ids behaviour out of the existing
`find_some` method: especially with this change, the conditionals were
overwhelming the actual logic.

1 files changed, 19 insertions, 6 deletions

diff --git a/activerecord/lib/active_record/relation/finder_methods.rb b/activerecord/lib/active_record/relation/finder_methods.rb
index 3aa38dcf78..fc4e891b02 100644
--- a/activerecord/lib/active_record/relation/finder_methods.rb
+++ b/activerecord/lib/active_record/relation/finder_methods.rb
@@ -444,6 +444,10 @@ module ActiveRecord
     end
 
     def find_some(ids)
+      return find_some_ordered(ids) unless order_values.present?
+
+      result = where(primary_key => ids).to_a
+
       expected_size =
         if limit_value && ids.size > limit_value
           limit_value
@@ -454,18 +458,27 @@ module ActiveRecord
       # 11 ids with limit 3, offset 9 should give 2 results.
       if offset_value && (ids.size - offset_value < expected_size)
         expected_size = ids.size - offset_value
+      end
+
+      if result.size == expected_size
+        result
       else
-        ids = ids.first(expected_size) if order_values.empty?
+        raise_record_not_found_exception!(ids, result.size, expected_size)
       end
+    end
 
-      result = where(primary_key => ids).to_a
+    def find_some_ordered(ids)
+      ids = ids.slice(offset_value || 0, limit_value || ids.size) || []
+
+      result = except(:limit, :offset).where(primary_key => ids).to_a
+
+      if result.size == ids.size
+        pk_type = @klass.type_for_attribute(primary_key)
 
-      if result.size == expected_size
-        return result if order_values.present?
         records_by_id = result.index_by(&:id)
-        ids.collect { |id| records_by_id[id.to_i] }.compact
+        ids.map { |id| records_by_id.fetch(pk_type.cast(id)) }
       else
-        raise_record_not_found_exception!(ids, result.size, expected_size)
+        raise_record_not_found_exception!(ids, result.size, ids.size)
       end
     end