add migration to add invited users to group.invites, @lefnire I tried with _.each(db.users.find()) but doesnt seem to work for db records so I ended up using db.users.find().forEach... which instead seems to work. My first migration to cleanup deleted tags used _.each so I rewrote it using native forEach, just wanted to let you know that it is updated now.

migrations/20131028_cleanup_deleted_tags.js

@@ -1,4 +1,4 @@
-_.each(db.users.find(), function(user){
+db.users.find().forEach(function(user){
   var tags = user.tags;
 
   _.each(user.tasks, function(task){
@@ -6,7 +6,7 @@ _.each(db.users.find(), function(user){
       _.each(tags, function(tag){
         if(key == tag.id) delete task.tags[key];
       });
-    };
+    });
   });
 
   try {

migrations/20131029_add_invites_to_groups.js

@@ -0,0 +1,31 @@
+var groups = {};
+
+db.users.find().forEach(function(user){
+  if(user.invitations){
+    if(user.invitations.party){
+      groups[user.invitations.party.id] = groups[user.invitations.party.id] || [];
+      groups[user.invitations.party.id].push(user._id);
+    }
+
+    if(user.invitations.guilds){
+      _.each(user.invitations.guilds, function(guild){
+        groups[guild.id] = groups[guild.id] || [];
+        groups[guild.id].push(user._id);
+      });
+    }
+  }
+});
+
+_.each(groups, function(usersInvited, groupId){
+  var group = db.groups.findOne({_id: groupId});
+
+  if(group){
+    group.invites = usersInvited;
+
+    try {
+      db.groups.update({_id: groupId}, group);
+    } catch(e) {
+      print(e);
+    }
+  };
+});