Differentiate between single- and multi- props.

filter/txnBuf/query_merger.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package txnBuf
 
 import (
         "bytes"
         "sort"
 
@@ skipping 244 matching lines @@
 // The result of this function is the series of serialized properties, one per
 // order column, which represent this key/pm's first entry in the composite
 // index that would point to it (e.g. the one with `order` sort orders).
 func toComparableString(start, end []byte, order []ds.IndexColumn, k *ds.Key, pm ds.PropertyMap) (row, key []byte) {
         doCmp := true
         soFar := []byte{}
         ps := serialize.PropertyMapPartially(k, nil)
         for _, ord := range order {
                 row, ok := ps[ord.Property]
                 if !ok {
-                        if vals, ok := pm[ord.Property]; ok {
-                                row = serialize.PropertySlice(vals)
+                        if pslice := pm.Slice(ord.Property); len(pslice) > 0 {
+                                row = serialize.PropertySlice(pslice)
                         }
                 }
                 sort.Sort(row)
                 foundOne := false
                 for _, serialized := range row {
                         if ord.Descending {
                                 serialized = serialize.Invert(serialized)
                         }
                         if doCmp {
                                 maybe := serialize.Join(soFar, serialized)
@@ skipping 12 matching lines @@
                 }
                 if !foundOne {
                         return nil, nil
                 }
         }
         if end != nil && bytes.Compare(soFar, end) >= 0 {
                 return nil, nil
         }
         return soFar, ps["__key__"][0]
 }