Add DatastoreDB.replace({defaultPartition})

lib/src/db/db.dart

Index: lib/src/db/db.dart
diff --git a/lib/src/db/db.dart b/lib/src/db/db.dart
index 07c5efb7b5ac3b7bafedfcd0da4508e144c370c3..2562f8a852088011c2d5f8b59b939cc40e36a21e 100644
--- a/lib/src/db/db.dart
+++ b/lib/src/db/db.dart
@@ -247,9 +247,10 @@ class DatastoreDB {
   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);
   }
 
   /**
@@ -325,6 +326,14 @@ class DatastoreDB {
   Future commit({List<Model> inserts, List<Key> deletes}) {
     return _commitHelper(this, inserts: inserts, deletes: deletes);
   }
+
+  /**
+   * Returns a new [DatastoreDB] with the given [defaultPartition].
+   */
+  DatastoreDB replace({Partition defaultPartition}) {

[Søren Gjesse, 2015/02/19 11:59:51]

The method name 'replace' seems somewhat overloaded with operation you would
expect on a DatastoreDB instance. How about changing this to a DatastoreDB.from
constructor?

var existingDb = ...
var otherDb = new DatastoreDB.from(existingDb, defaultPartition: ...);

[kustermann, 2015/02/19 12:17:11]

Another constructor is of no value, since the existing one can do that as well.

Removed replace method now.

+    return new DatastoreDB(
+        datastore, modelDB: modelDB, defaultPartition: defaultPartition);
+  }
 }
 
 Future _commitHelper(DatastoreDB db,