diff --git a/lib/cwmp.coffee b/lib/cwmp.coffee
index e5ef607..27e101c 100644
--- a/lib/cwmp.coffee
+++ b/lib/cwmp.coffee
@@ -64,8 +64,7 @@ updateDevice = (currentRequest, actions, callback) ->
     return
 
   now = new Date(Date.now())
-  updates = {}
-  deletes = {}
+  update = {'$set' : {}, '$unset' : {}}
 
   if actions.parameterValues?
     for p in actions.parameterValues
@@ -74,36 +73,36 @@ updateDevice = (currentRequest, actions, callback) ->
 
       path = if common.endsWith(p[0], '.') then p[0] else "#{p[0]}."
       if v == origValue
-        deletes["#{path}_orig"] = 1
+        update['$unset']["#{path}_orig"] = 1
       else
-        updates["#{path}_orig"] = origValue
-      updates["#{path}_value"] = v
-      updates["#{path}_timestamp"] = now
+        update['$set']["#{path}_orig"] = origValue
+      update['$set']["#{path}_value"] = v
+      update['$set']["#{path}_timestamp"] = now
       if p[2]?
-        updates["#{path}_type"] = p[2]
+        update['$set']["#{path}_type"] = p[2]
       else
-        deletes["#{path}_type"] = 1
+        update['$unset']["#{path}_type"] = 1
 
   if actions.deletedObjects?
     for p in actions.deletedObjects
-      deletes[p] = 1
+      update['$unset'][p] = 1
 
   if actions.instanceName?
     for i in actions.instanceName
-      updates["#{i[0]}._name"] = i[1]
+      update['$set']["#{i[0]}._name"] = i[1]
 
   if actions.parameterNames?
     for p in actions.parameterNames
       if OBJECT_REGEX.test(p[0])
         path = p[0]
         if INSTANCE_REGEX.test(p[0])
-          updates["#{path}_instance"] = true
+          update['$set']["#{path}_instance"] = true
         else
-          updates["#{path}_object"] = true
+          update['$set']["#{path}_object"] = true
       else
         path = "#{p[0]}."
-      updates["#{path}_writable"] = p[1] if p[1]?
-      updates["#{path}_timestamp"] = now
+      update['$set']["#{path}_writable"] = p[1] if p[1]?
+      update['$set']["#{path}_timestamp"] = now
 
       # Add parameter (sans any dot suffix) if has an alias
       if (a = parameters.getAlias(pp = path.slice(0, -1)))?
@@ -113,14 +112,17 @@ updateDevice = (currentRequest, actions, callback) ->
   if actions.customCommands?
     for p in actions.customCommands
       commandName = p[0]
-      updates["_customCommands.#{commandName}._value"] = p[1]
-      updates["_customCommands.#{commandName}._timestamp"] = now
+      update['$set']["_customCommands.#{commandName}._value"] = p[1]
+      update['$set']["_customCommands.#{commandName}._timestamp"] = now
 
   if actions.set?
-    common.extend(updates, actions.set)
+    common.extend(update['$set'], actions.set)
 
-  if Object.keys(updates).length > 0 or Object.keys(deletes).length > 0
-    db.devicesCollection.update({'_id' : currentRequest.deviceId}, {'$set' : updates, '$unset' : deletes}, {}, (err, count) ->
+  for k of update
+    delete update[k] if Object.keys(update[k]).length == 0
+
+  if Object.keys(update).length
+    db.devicesCollection.update({'_id' : currentRequest.deviceId}, update, {}, (err, count) ->
       throw err if err
       # Clear aliases cache if there's a new aliased parameter that has not been included in aliases cache
       if newAliases?
diff --git a/lib/presets.coffee b/lib/presets.coffee
index 1440451..7b1a5a0 100644
--- a/lib/presets.coffee
+++ b/lib/presets.coffee
@@ -28,7 +28,11 @@ exports.getDevicePreset = (deviceId, presets, objects, aliases, callback) ->
   # only fetch relevant params
   projection = {_id : 1}
   for p in presets
-    p.precondition = query.expand(p.precondition, aliases)
+    if common.typeOf(p.precondition) is common.STRING_TYPE
+      p.precondition = query.expand(JSON.parse(p.precondition), aliases)
+    else
+      # Accept an object for backward compatiblity
+      p.precondition = query.expand(p.precondition ? {}, aliases)
     mongoQuery.projection(p.precondition, projection)
 
     for c in p.configurations
diff --git a/package.json b/package.json
index 271841c..cb38d97 100644
--- a/package.json
+++ b/package.json
@@ -20,10 +20,10 @@
     "bin": "bin"
   },
   "dependencies": {
-    "libxmljs": "~0.8.1",
-    "redis": "~0.10.0",
-    "hiredis": "~0.1.15",
-    "mongodb": "~1.3.23"
+    "libxmljs": "~0.9.0",
+    "redis": "~0.10.1",
+    "hiredis": "~0.1.16",
+    "mongodb": "~1.4.4"
   },
   "devDependencies": {
     "coffee-script": "~1.7.1"