Auto-project on distinct inequality fields.

service/datastore/query.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package datastore
 
 import (
         "bytes"
         "fmt"
         "sort"
@@ skipping 555 matching lines @@
                 ineqFiltLowIncl:  q.ineqFiltLowIncl,
                 ineqFiltLowSet:   q.ineqFiltLowSet,
                 ineqFiltHigh:     q.ineqFiltHigh,
                 ineqFiltHighIncl: q.ineqFiltHighIncl,
                 ineqFiltHighSet:  q.ineqFiltHighSet,
         }
 
         if q.project != nil {
                 ret.project = q.project.ToSlice()
                 ret.distinct = q.distinct && q.project.Len() > 0
+
+                // If we're DISTINCT && have an inequality filter, we must project that
+                // inequality property as well.
+                if ret.distinct && ret.ineqFiltProp != "" && !q.project.Has(ret.ineqFiltProp) {
+                        ret.project = append([]string{ret.ineqFiltProp}, ret.project...)
+                }
         }
 
         seenOrders := stringset.New(len(q.order))
 
         // if len(q.order) > 0, we already enforce that the first order
         // is the same as the inequality above. Otherwise we need to add it.
         if len(q.order) == 0 && q.ineqFiltProp != "" {
                 ret.orders = []IndexColumn{{Property: q.ineqFiltProp}}
                 seenOrders.Add(q.ineqFiltProp)
         }
@@ skipping 141 matching lines @@
         if q.keysOnly {
                 p("KeysOnly")
         }
 
         if _, err := ret.WriteRune(')'); err != nil {
                 panic(err)
         }
 
         return ret.String()
 }