Microsoft Dynamics 2011 N:N LINQ query with where clause containing Guid - linq

Question

I have constructed a simple query to return a Users Team membership (N: N relationship). This works fine for all users, however, when I add a where clause to restrict to a specific user it throws a fault exception (see stack trace below).
Strangely this works fine with "where Users.FullName.StartsWith("Alex")". Does the Dynamics CRM SDK LINQ implementation not support Guides in where clauses?
Any advice?
Example code
using (var service = new OrganizationService("Xrm"))
{
using (var xrm = new XrmServiceContext(service))
{
var AlexUser = xrm.SystemUserSet.Where(p => p.FullName.StartsWith("Alex")).First();
var AlexID = AlexUser.Id;
var Test =
from Users in xrm.SystemUserSet
join TeamMemberships in xrm.TeamMembershipSet on Users.Id equals TeamMemberships.SystemUserId
join Teams in xrm.TeamSet on TeamMemberships.TeamId equals Teams.Id
where Users.Id == AlexID // <-- problematic where clause
orderby Users.FullName
select new
{
FullName = Users.FullName,
UserID = Users.Id,
TeamName = Teams.Name
};
var Test1 = Test.ToList();
}
}
Stacktrace:
Server stack trace: at
System.ServiceModel.Channels.ServiceChannel.HandleReply(ProxyOperationRuntime
operation, ProxyRpc& rpc) at
System.ServiceModel.Channels.ServiceChannel.Call(String action,
Boolean oneway, ProxyOperationRuntime operation, Object[] ins,
Object[] outs, TimeSpan timeout) at
System.ServiceModel.Channels.ServiceChannel.Call(String action,
Boolean oneway, ProxyOperationRuntime operation, Object[] ins,
Object[] outs) at
System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage
methodCall, ProxyOperationRuntime operation) at
System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage
message)
Exception rethrown at [0]: at
System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage
reqMsg, IMessage retMsg) at
System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData&
msgData, Int32 type) at
Microsoft.Xrm.Sdk.IOrganizationService.Execute(OrganizationRequest
request) at
Microsoft.Xrm.Sdk.Client.OrganizationServiceProxy.ExecuteCore(OrganizationRequest
request) at
Microsoft.Xrm.Sdk.Client.OrganizationServiceProxy.Execute(OrganizationRequest
request) at
Microsoft.Xrm.Client.Services.OrganizationService.<>c__DisplayClass19.b__18(IOrganizationService
s) at
Microsoft.Xrm.Client.Services.OrganizationService.InnerOrganizationService.UsingService[TResult](Func2 action) at Microsoft.Xrm.Client.Services.OrganizationService.Execute(OrganizationRequest request) at Microsoft.Xrm.Sdk.Client.OrganizationServiceContext.Execute(OrganizationRequest request) at Microsoft.Xrm.Sdk.Linq.QueryProvider.RetrieveEntityCollection(OrganizationRequest request, NavigationSource source) at Microsoft.Xrm.Sdk.Linq.QueryProvider.Execute(QueryExpression qe, Boolean throwIfSequenceIsEmpty, Boolean throwIfSequenceNotSingle, Projection projection, NavigationSource source, List1 linkLookups,
String& pagingCookie, Boolean& moreRecords) at
Microsoft.Xrm.Sdk.Linq.QueryProvider.Execute[TElement](QueryExpression
qe, Boolean throwIfSequenceIsEmpty, Boolean throwIfSequenceNotSingle,
Projection projection, NavigationSource source, List1 linkLookups) at Microsoft.Xrm.Sdk.Linq.QueryProvider.Execute[TElement](Expression expression) at Microsoft.Xrm.Sdk.Linq.QueryProvider.GetEnumerator[TElement](Expression expression) at Microsoft.Xrm.Sdk.Linq.Query1.GetEnumerator() at
System.Collections.Generic.List1..ctor(IEnumerable1 collection)
at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source) at
aspirets.crm.test.Program.Main(String[] args) in
C:\Users\a_marshall\documents\visual studio
2010\Projects\aspirets.crm\aspirets.crm.test\Program.cs:line 37 at
System.AppDomain._nExecuteAssembly(RuntimeAssembly assembly, String[]
args) at System.AppDomain.ExecuteAssembly(String assemblyFile,
Evidence assemblySecurity, String[] args) at
Microsoft.VisualStudio.HostingProcess.HostProc.RunUsersAssembly()
at System.Threading.ThreadHelper.ThreadStart_Context(Object state)
at System.Threading.ExecutionContext.Run(ExecutionContext
executionContext, ContextCallback callback, Object state, Boolean
ignoreSyncCtx) at
System.Threading.ExecutionContext.Run(ExecutionContext
executionContext, ContextCallback callback, Object state) at
System.Threading.ThreadHelper.ThreadStart()

Answer 1

Instead of Users.Id, try Users.SystemUserId. Similarly, instead of Teams.Id, try Teams.TeamId.
As for the reason why this works, I'm not aware of any documentation that states this, but because entities in the generated early-binding file inherit from Entity, they necessarily have an Id property. However, because the early-bound OrganizationServiceContext maps entity attributes directly to the CRM database, the tables of which don't contain an Id column, using the Id attribute with the LINQ provider won't work, so you'd have to use the actual database/schema names.