Subsonic BatchQuery.Queue causing ‘Can’t decide which property to consider the key…’ exception

I'm just getting started with Subsonic 3.0 ActiveRecord and am trying to implement a batch query like the one in the SubSonic docs. I'm using a batch so I can query a User and a list of the users Orders in one shot.

When I call the BatchQuery.Queue() method, adding my "select user" query, SubSonic throws the following exception:

System.InvalidOperationException : Can't decide which property to consider the Key – you can create one called 'ID' or mark one with SubSonicPrimaryKey attribute

The code is as follows:

var db = new MyDB();
var userQuery = from u in db.Users //gets user by uid
                where u.uid == 1
                select u;

var provider = ProviderFactory.GetProvider();
var batch = new BatchQuery(provider);
batch.Queue(userQuery); //exception here

//create and add "select users orders" query here...

First things first – Why this error? My SubSonic Users object knows it's PK. "uid" is the PK in the database and the generated code reflects this. And I thought SubSonicPrimaryKey attribute was for the SimpleRepository? Is this way of batching not for ActiveRecord?

I could ask a number of other questions, but I'll leave it at that. If anyone can help me figure out what is going on and how to issue 2 batched queries I'd be grateful!

Edit – after further investigation

I ran through the source code with the debugger. Adam is correct – the ToSchemaTable() method in Objects.cs is apparently building out my schema and failing to find a PK. At the very end, it tries to find a column property named "ID" and flags this as the PK, otherwise it throws the exception. I added a check for "UID" and this works!

Still… I'm confused. I'm admittedly a bit lost after peeling back layer after layer of the source, but it seems like this portion of code is trying to build up a schema for my table and completely ignoring my generated User class – which quite nicely identifies which column/property is the PK! It doesn't seem quite right that I'd be required to name all keys "ID" w/ ActiveRecord.