Question

This is a follow up question to the one answered here: Excluding dates from Linq Query in MVC .net application – which I’m very grateful for.

I’m hoping that someone can check my syntax in my Linq query below – to confirm if it’s the best way to build the query up, or if my use of the syntax is inefficient.

public class Room 
{ 
    public int RoomId { get; set; } 
    [Display(Name = "Room Name")] 
    public string Name { get; set; } 
    public bool Disabled { get; set; } 
    public virtual ICollection<Client> Clients { get; set; } 
    } 

public class Client 
{ 
    public int ClientId { get; set; } 
    public int RoomId { get; set; } 
    public string ClientName { get; set; } 
    public DateTime Arrival { get; set; } 
    public DateTime Departure { get; set; } 
    public virtual Room Room { get; set; } 
} 

Clients lists a row for each client who has a particuar room booked. I have 3 rooms, Room 1, Room 2, and Room 3. So entries in the client table could be:

Client 1, Room 1, Mr Smith, Arr: 2012-07-08, Dep: 2012-07-10
Client 2, Room 1, Mr Jones, Arr: 2012-07-14, Dep: 2012-07-20
Client 3, Room 2, Mr Alas,  Arr: 2012-07-12, Dep: 2012-07-15

Given an arrival and departure date, I’m trying to take my whole list of rooms, and take away any that have a client staying where the arrival or departure dates overlap. So using the data above, if I had an arrival date of 2012-07-12 and a departure date of 2012-07-13, then Room 2 would not be available, however, Room 1, does not have any bookings spanning that date – so Room 1 I want to leave in my result set.

So my Linq query (I’m new to Linq, so please point out where I may be going wrong) is:

var dteFrom = DateTime.Parse("2012-07-12");
var dteTo = DateTime.Parse("2012-07-13");
var rooms = (from r in Rooms
                where !r.Clients.Any(
            client =>
                ( dteFrom >= client.Arrival && dteFrom <= client.Departure )
                ||
                ( dteTo >= client.Arrival && dteFrom <= client.Departure )
                ||
                ( dteFrom <= client.Arrival && dteTo >= client.Departure )
                )
            select r);

Given that I’m looking to include ALL rooms, EXCEPT any that meet the criteria, can anyone confirm that my use of .Any and ! and || are correct, as far as LINQ goes?

Is there any better way within the syntax, of excluding records from the Rooms list?

Thank you again for any help,

Mark

Answer 1

Looks fine to me – one thing that may help readability would be to compose your query in two steps:

var prebookedRooms = rooms
    .Where(room => room.Clients.Any(client => 
    (dteFrom >= client.Arrival && dteFrom <= client.Departure) ||
    (dteTo >= client.Arrival && dteFrom <= client.Departure)   ||
    (dteFrom <= client.Arrival && dteTo >= client.Departure)));

var freeRooms = rooms.Except(prebookedRooms);

Remembering that the query is only executed, when the results are enumerated – so there’s no performance cost to doing this in two steps.