Refactor keys and queries in datastore service and implementation.

service/datastore/index.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"
+        "strings"
 )
 
 const MaxIndexColumns = 64
 
 type IndexDirection bool
 
 const (
         // ASCENDING is false so that it's the default (zero) value.
         ASCENDING  IndexDirection = false
         DESCENDING                = true
 )
 
 func (i IndexDirection) String() string {
         if i == ASCENDING {
                 return "ASCENDING"
         }
         return "DESCENDING"
 }
 
 type IndexColumn struct {
         Property  string
         Direction IndexDirection
 }
 
+func ParseIndexColumn(spec string) (IndexColumn, error) {
+        col := IndexColumn{}
+        if strings.HasPrefix(spec, "-") {
+                col.Direction = DESCENDING
+                col.Property = strings.TrimSpace(spec[1:])
+        } else if strings.HasPrefix(spec, "+") {
+                return col, fmt.Errorf("datastore: invalid order: %q", spec)
+        } else {
+                col.Direction = ASCENDING
+                col.Property = strings.TrimSpace(spec)
+        }
+        if col.Property == "" {
+                return col, fmt.Errorf("datastore: empty order")
+        }
+        return col, nil
+}
+
 func (i IndexColumn) cmp(o IndexColumn) int {
         // sort ascending first
         if i.Direction == ASCENDING && o.Direction == DESCENDING {
                 return -1
         } else if i.Direction == DESCENDING && o.Direction == ASCENDING {
                 return 1
         }
         return cmpString(i.Property, o.Property)()
 }
 
+func (i IndexColumn) String() string {
+        ret := ""
+        if i.Direction == DESCENDING {
+                ret = "-"
+        }
+        return ret + i.Property
+}
+
+func (i IndexColumn) GQL() string {
+        if i.Direction == DESCENDING {
+                return gqlQuoteName(i.Property) + " DESC"
+        }
+        return gqlQuoteName(i.Property)
+}
+
 type IndexDefinition struct {
         Kind     string
         Ancestor bool
         SortBy   []IndexColumn
 }
 
 func (id *IndexDefinition) Equal(o *IndexDefinition) bool {
         if id.Kind != o.Kind || id.Ancestor != o.Ancestor || len(id.SortBy) != len(o.SortBy) {
                 return false
         }
@@ skipping 143 matching lines @@
         }
         for _, sb := range i.SortBy {
                 ret.WriteRune('/')
                 if sb.Direction == DESCENDING {
                         ret.WriteRune('-')
                 }
                 ret.WriteString(sb.Property)
         }
         return ret.String()
 }