How to use returned linq variable?

Question

I've decided to take a quick look into the LINQ side of things, as opposed to just using a straight up foreach loop, but i'm having some trouble getting it to work, mainly due to datatypes i believe.

So i've got this, so far;

var selectedSiteType = from sites in siteTypeList
                                   where sites.SiteTypeID == temp
                                   select sites;

siteTypeList is a list of SiteTypes. I'm trying to find a particular one (Which i've denounced with variable "temp".

How do i then use this selected SiteType AS a SiteType? When i try and pass "selectedSiteType" through to another function, like so;

mSiteTypeSub.EditSitetype(selectedSiteType);

note: I tried with providing an index, as if selectedSiteType was a list / Array, but that didnt work either, i get the following error:

Argument 1: cannot convert from 
'System.Collections.Generic.IEnumerable<DeviceManager_take_2.SiteType>' to 
'DeviceManager_take_2.SiteType' 

Am i missing something? perhaps a cast of some kind? Like i said i'm new to this and am struggling to get my head around this. Chances are i've got the whole concept wrong and bingbangbosh i've made a fool of myself!

Cheers in advance.

Answer 1

Use First / FirstOrDefault / Single / SingleOrDefault to get an item of the particular type from the collection.

   var value = selectedSiteType.First(); 
   // returns the first item of the collection

   var value = selectedSiteType.FirstOrDefault(); 
   // returns the first item of the collection or null if none exists

   var value = selectedSiteType.Single(); 
   // returns the only one item of the collection, exception is thrown if more then one exists

   var value = selectedSiteType.SingleOrDefault(); 
   // returns the only item from the collection or null, if none exists. If the collection contains more than one item, an exception is thrown. 

Answer 2

If your return type is a single:

   var selectedSiteType = (from sites in siteTypeList
                                       where sites.SiteTypeID == temp
                                       select sites).SingleOrDefault();

If a list (potentially more than one item):

 var selectedSiteType = (from sites in siteTypeList
                                       where sites.SiteTypeID == temp
                                       select sites).ToList();

It's the SingleOrDefault / ToList that you're missing from your query.

Answer 3

Shane,

I'm not going to improve on the previous answers. They were both correct. I am going to try and explain a little bit to you, so that you understand it in the future a bit better.

What happens, when you write a piece of code like:

var selectedSiteType = from sites in siteTypeList
                               where sites.SiteTypeID == temp
                               select sites;

you don't put the answer into the var (selectedSiteType), instead, you are creating an expression tree, that is evaluated ONLY when you actually use it (in a foreach, or by calling one of the methods (like .First(), .ToList(), SingleOrDefault(), etc).

The default return type of a from statement, is an IEnumerable<>, but if you call the .First() or .SingleOrDefault() (etc), you will dive into that IEnumerable<> and get a specific item.

I hope this helps you better understand what is going on.

Lemme know if I can add anything or if I got anything wrong.

Cheers,

Max