datastore/metadata.go
func KindProperties(ctx context.Context, kind string) (map[string][]string, error) {
	// TODO(djd): Support range queries.
	kindKey := NewKey(ctx, kindKind, kind, 0, nil)
	q := NewQuery(propertyKind).Ancestor(kindKey)

	propMap := map[string][]string{}
	props := []struct {
		Repr []string `datastore:"property_representation"`
	}{}

	keys, err := q.GetAll(ctx, &props)
	if err != nil {
		return nil, err
	}
	for i, p := range props {
		propMap[keys[i].StringID()] = p.Repr
	}
	return propMap, nil
}
func KindProperties(ctx context.Context, kind string) (map[string][]string, error) {
	// TODO(djd): Support range queries.
	kindKey := NewKey(ctx, kindKind, kind, 0, nil)
	q := NewQuery(propertyKind).Ancestor(kindKey)

	propMap := map[string][]string{}
	props := []struct {
		Repr []string `datastore:"property_representation"`
	}{}

	keys, err := q.GetAll(ctx, &props)
	if err != nil {
		return nil, err
	}
	for i, p := range props {
		propMap[keys[i].StringID()] = p.Repr
	}
	return propMap, nil
}
// KindProperties returns all the indexed properties for the given kind.
// The properties are returned as a map of property names to a slice of the
// representation types. The representation types for the supported Go property
// types are:
//   "INT64":     signed integers and time.Time
//   "DOUBLE":    float32 and float64
//   "BOOLEAN":   bool
//   "STRING":    string, []byte and ByteString
//   "POINT":     appengine.GeoPoint
//   "REFERENCE": *Key
//   "USER":      (not used in the Go runtime)