Add DatastoreDB.replace({defaultPartition})

lib/src/db/db.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of gcloud.db;
 
 /**
  * A function definition for transactional functions.
  *
  * The function will be given a [Transaction] object which can be used to make
@@ skipping 229 matching lines @@
     }
     return propertyName;
   }
 }
 
 class DatastoreDB {
   final datastore.Datastore datastore;
   final ModelDB _modelDB;
   Partition _defaultPartition;
 
-  DatastoreDB(this.datastore, {ModelDB modelDB})
-      : _modelDB = modelDB != null ? modelDB : new ModelDBImpl() {
-    _defaultPartition = new Partition(null);
+  DatastoreDB(this.datastore, {ModelDB modelDB, Partition defaultPartition}) :
+      _modelDB = modelDB != null ? modelDB : new ModelDBImpl() {
+      _defaultPartition =
+          defaultPartition != null ? defaultPartition : new Partition(null);
   }
 
   /**
    * The [ModelDB] used to serialize/deserialize objects.
    */
   ModelDB get modelDB => _modelDB;
 
   /**
    * Gets the empty key using the default [Partition].
    *
@@ skipping 110 matching lines @@
 
 Future<List<Model>> _lookupHelper(
     DatastoreDB db, List<Key> keys,
     {datastore.Transaction datastoreTransaction}) {
   var entityKeys = keys.map(db.modelDB.toDatastoreKey).toList();
   return db.datastore.lookup(entityKeys, transaction: datastoreTransaction)
       .then((List<datastore.Entity> entities) {
     return entities.map(db.modelDB.fromDatastoreEntity).toList();
   });
 }