Auto-project on distinct inequality fields.

service/datastore/finalized_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 47 matching lines @@
 // EventuallyConsistent returns true iff this query will be eventually
 // consistent. This is true when the query is a non-ancestor query, or when it's
 // an ancestory query with the 'EventualConsistency(true)' option set.
 func (q *FinalizedQuery) EventuallyConsistent() bool {
         return q.eventuallyConsistent
 }
 
 // Project is the list of fields that this query projects on, or empty if this
 // is not a projection query.
 func (q *FinalizedQuery) Project() []string {
-        if len(q.project) == 0 {
+        // For distinct queries with an inequality filter, one must first project the
+        // inequality field.
+        size := len(q.project)
+        ineqDistinctProject := ""
+        if q.distinct && q.ineqFiltProp != "" {
+                ineqDistinctProject = q.ineqFiltProp
+                size++
+        }
+
+        if size == 0 {
                 return nil
         }
-        ret := make([]string, len(q.project))
-        copy(ret, q.project)
+        ret := make([]string, 0, size)
+        if ineqDistinctProject != "" {
+                ret = append(ret, ineqDistinctProject)
+        }
+        ret = append(ret, q.project...)

[iannucci, 2016/02/27 00:58:51]

ditch this whole thing

         return ret
 }
 
 // Distinct returnst true iff this is a distinct projection query. It will never
 // be true for non-projection queries.
 func (q *FinalizedQuery) Distinct() bool {
         return q.distinct
 }
 
 // KeysOnly returns true iff this query will only return keys (as opposed to a
@@ skipping 247 matching lines @@
         if q.ineqFiltProp == "__key__" {
                 if q.ineqFiltLowSet && !q.ineqFiltLow.Value().(*Key).Valid(false, aid, ns) {
                         return ErrInvalidKey
                 }
                 if q.ineqFiltHighSet && !q.ineqFiltHigh.Value().(*Key).Valid(false, aid, ns) {
                         return ErrInvalidKey
                 }
         }
         return nil
 }