Add datastore dumper tool.

service/datastore/dumper/dumper_example_test.go

Index: service/datastore/dumper/dumper_example_test.go
diff --git a/service/datastore/dumper/dumper_example_test.go b/service/datastore/dumper/dumper_example_test.go
new file mode 100644
index 0000000000000000000000000000000000000000..2f44dbc504ee05f012ac29be884423f01f30fd79
--- /dev/null
+++ b/service/datastore/dumper/dumper_example_test.go
@@ -0,0 +1,83 @@
+// Copyright 2016 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 dumper
+
+import (
+	"fmt"
+
+	"github.com/luci/gae/impl/memory"
+	"github.com/luci/gae/service/datastore"
+	"golang.org/x/net/context"
+)
+
+type ExampleModel struct {
+	Kind   string         `gae:"$kind,Example"`
+	ID     int64          `gae:"$id"`
+	Parent *datastore.Key `gae:"$parent"`
+
+	Vals      []string
+	Number    int64
+	HexNumber int64
+}
+
+func ExampleConfig_Query() {
+	c := context.Background()
+	c = memory.Use(c)
+
+	ds := datastore.Get(c)
+	root := ds.MakeKey("Parent", 1)
+	models := []*ExampleModel{
+		{ID: 1, Vals: []string{"hi", "there"}, Number: 10, HexNumber: 20},
+		{ID: 2, Vals: []string{"other"}, Number: 11, HexNumber: 21},
+		{ID: 1, Parent: root, Vals: []string{"child", "ent"}},
+		{Kind: "Other", ID: 1, Vals: []string{"other"}, Number: 11, HexNumber: 21},
+	}
+	if err := ds.Put(models); err != nil {
+		panic(err)
+	}
+	// indexes must be up-to-date here.
+	ds.Testable().CatchupIndexes()
+
+	_, err := Config{
+		PropFilters: PropFilterMap{
+			{"Example", "HexNumber"}: func(p datastore.Property) string {
+				return fmt.Sprintf("0x%04x", p.Value())
+			},
+		},
+		KindFilters: KindFilterMap{
+			"Other": func(key *datastore.Key, pm datastore.PropertyMap) string {
+				return "I AM A BANANA"
+			},
+		},
+	}.Query(c, nil)
+	if err != nil {
+		panic(err)
+	}
+
+	// Output:
+	// dev~app::/Example,1:
+	//   "HexNumber": [0x0014]
+	//   "Number": [PTInt(10)]
+	//   "Vals": [
+	//     PTString("hi"),
+	//     PTString("there")
+	//   ]
+	//
+	// dev~app::/Example,2:
+	//   "HexNumber": [0x0015]
+	//   "Number": [PTInt(11)]
+	//   "Vals": [PTString("other")]
+	//
+	// dev~app::/Other,1:
+	//   I AM A BANANA
+	//
+	// dev~app::/Parent,1/Example,1:
+	//   "HexNumber": [0x0000]
+	//   "Number": [PTInt(0)]
+	//   "Vals": [
+	//     PTString("child"),
+	//     PTString("ent")
+	//   ]
+}