linq sort many 2 many question

Question

My main entity is called [Contract]. Contract has a many 2 many relationship w/ [Service].

When I query for a list of Contracts I grab the 1st Service available like this:

IQueryable<Contract> q = ctx.Contracts.Skip(startRow - 1).Take(pgSize);
q.Select(c =>
         new ContractSearchResult()
         {
           ContractID = c.ContractID,
           FirstService = c.Contract2Service.FirstOrDefault().Service.Name,
           ServiceCount = c.Contract2Service.Count,
         }
        ).ToList();

(When I display this list I show the FirstService if there's only 1. If > 1 I show "My1stService (3)" to show I'm seeing the 1st of 3 services) This works fine.

My question is this:

Is there any way to sort by FirstService? Or is this impossible? I haven't found a way of expressing this in linq and allow for paging.

Any help would be appreciated.

Answer 1

You need to OrderBy before you page.

var result = ctx.Contracts
    .Select(c =>
        new ContractSearchResult()
        {
            ContractID = c.ContractID,
            FirstService = c.Contract2Service.FirstOrDefault().Service.Name,
            ServiceCount = c.Contract2Service.Count,
        })
 .OrderBy(x => x.FirstService)
 .Skip(startRow - 1)
 .Take(pgSize)
 .ToList();

Also note that FirstOrDefault can return null and you should check for that. If you know that it will (or should) never be null then use First instead.

Answer 2

q.OrderBy(c => c.Contract2Service.FirstOrDefault().Service.Name)
 .Select(c =>
        new ContractSearchResult()
        {
            ContractID = c.ContractID,
            FirstService = c.Contract2Service.FirstOrDefault().Service.Name,
            ServiceCount = c.Contract2Service.Count,
        }
    )
 .ToList();

Unless I'm missing something in your question (which is possible), it should be as simple as calling OrderBy() after your call to Select()