datastore: Update AllocateIDs to take keys.

service/datastore/interface.go

Index: service/datastore/interface.go
diff --git a/service/datastore/interface.go b/service/datastore/interface.go
index c70dd53c54095804b6f88826e452f27f4707a14a..701a0df556caadcfea4b8635aa5d9a46b732e059 100644
--- a/service/datastore/interface.go
+++ b/service/datastore/interface.go
@@ -45,12 +45,14 @@ func (bl BoolList) Any() bool {
 // using this package's GetPLS function.
 type Interface interface {
 	// AllocateIDs allows you to allocate IDs from the datastore without putting
-	// any data. `incomplete` must be a PartialValid Key. If there's no error,
-	// a contiguous block of IDs of n length starting at `start` will be reserved
-	// indefinitely for the user application code for use in new keys. The
-	// appengine automatic ID generator will never automatically assign these IDs
-	// for Keys of this type.
-	AllocateIDs(incomplete *Key, n int) (start int64, err error)
+	// any data. The supplied keys must be PartialValid and share the same entity
+	// type.
+	//
+	// If there's no error, a new slice of complete keys will be returned with
+	// reserved integer IDs // assigned to them. The appengine automatic ID
+	// generator will never automatically assign these IDs to any other Keys of
+	// this type.
+	AllocateIDs(keys ...*Key) ([]*Key, error)
 
 	// KeyForObj extracts a key from src.
 	//
@@ -77,6 +79,10 @@ type Interface interface {
 	// specified parameters.
 	NewKey(kind, stringID string, intID int64, parent *Key) *Key
 
+	// NewIncompleteKeys allocates count incomplete keys sharing the same kind and
+	// parent. It is useful as input to AllocateIDs.
+	NewIncompleteKeys(count int, kind string, parent *Key) []*Key
+
 	// NewKeyToks constructs a new key in the current appID/Namespace, using the
 	// specified key tokens.
 	NewKeyToks([]KeyTok) *Key