I'm having trouble with following EF lambda expressions.

partial void StatusCallBackRequired_PreprocessQuery(ref IQueryable<PatientsTelephoneFollowupDetail> query)
{
    var newList = PatientsTelephoneFollowupDetails.OrderBy(x => x.Id).ToList();
    query = query.Where(p => p.PatientsMasterItem.PatientsTelephoneFollowupDetail.OrderByDescending(c => c.Id).FirstOrDefault(c => c.Status == "7") != null);
 }

The error is:

'Microsoft.LightSwitch.IOrderedDataServiceQueryable' does not contain a definition for 'ToList' and no extension method 'ToList' accepting a first argument of type 'Microsoft.LightSwitch.IOrderedDataServiceQueryable' could be found (are you missing a using directive or an assembly reference?)

I have already included system.linq namespace.

EDIT:(the results based on D Stanley code)

The sample data can be found below and I'm looking to retrieve the highlighted record

However the current output is

Changing query to query.select returns only one record but it's is the wrong record.

• c#
• linq
• entity-framework
• linq-to-sql
• visual-studio-lightswitch

Couple of things to try:

cast to IEnumerable<T>:

var newList = ((IEnumerable<PatientsTelephoneFollowupDetail>)PatientsTelephoneFollowupDetails.OrderBy(x => x.Id)).ToList();

Initialize the list from the query result:

var newList = new List<PatientsTelephoneFollowupDetail>(PatientsTelephoneFollowupDetails.OrderBy(x => x.Id)));

EDIT Looks like LightSwitch doesn't implement IEnumerable<T>. Two more things to try:

Assuming it implements IEnumerable, use IEnumerable.Cast<T>():

var newList = new List<PatientsTelephoneFollowupDetail>(
    PatientsTelephoneFollowupDetails.OrderBy(x => x.Id)
        .Cast<PatientsTelephoneFollowupDetail>()
    );

brute force:

var newList = new List<PatientsTelephoneFollowupDetail>();
foreach(var item in PatientsTelephoneFollowupDetails.OrderBy(x => x.Id))
    newList.Add(item);

You need to find the definition of this type: Microsoft.LightSwitch.IOrderedDataServiceQueryable

Once you've found it, confirm:

Does it implement IEnumerable<T>? If so, your code can't reach System.Linq.Enumerable. You say you are using System.Linq, so make sure your project is referencing System.Core.dll .

If not, does it implement IEnumerable? If so, you can write a foreach loop and add each item to a List<T> that you make.

If not, examine the properties. There is usually some way to get at the something you can write a loop against.