Base.merge_conditions is no longer needed

activerecord/lib/active_record/base.rb

@@ -1238,20 +1238,6 @@ def sti_name
         store_full_sti_class ? name : name.demodulize
       end
 
-      # Merges conditions so that the result is a valid +condition+
-      def merge_conditions(*conditions)
-        segments = []
-
-        conditions.each do |condition|
-          unless condition.blank?
-            sql = sanitize_sql(condition)
-            segments << sql unless sql.blank?
-          end
-        end
-
-        "(#{segments.join(') AND (')})" unless segments.empty?
-      end
-
       def unscoped
         @unscoped ||= Relation.new(self, arel_table)
         finder_needs_type_condition? ? @unscoped.where(type_condition) : @unscoped

activerecord/lib/active_record/relation/query_methods.rb

@@ -167,8 +167,8 @@ def build_where(*args)
       builder = PredicateBuilder.new(table.engine)
 
       conditions = if [String, Array].include?(args.first.class)
-        merged = @klass.send(:merge_conditions, args.size > 1 ? Array.wrap(args) : args.first)
-        Arel::SqlLiteral.new(merged) if merged
+        sql = @klass.send(:sanitize_sql, args.size > 1 ? args : args.first)
+        Arel::SqlLiteral.new("(#{sql})") if sql.present?
       elsif args.first.is_a?(Hash)
         attributes = @klass.send(:expand_hash_conditions_for_aggregates, args.first)
         builder.build_from_hash(attributes, table)