How to use Lambda in LINQ select statement

Question

I am trying to select stores using a lambda function and converting the result to a SelectListItem so I can render it. However it is throwing a "Type of Expression in Select Clause is Incorrect" error:

IEnumerable<SelectListItem> stores =
    from store in database.Stores
    where store.CompanyID == curCompany.ID
    select (s => new SelectListItem { Value = s.ID, Text = s.Name} );
ViewBag.storeSelector = stores;

What am I doing wrong?

EDIT:

Also, how do I convert Int to String in this situation? The following does not work:

select (s => new SelectListItem { Value = s.ID.ToString(), Text = s.Name} );
select (s => new SelectListItem { Value = s.ID + "", Text = s.Name} );

EDIT 2:

Figure out the Int to String conversion. It is so typical of Microsoft to forget to include an int2string conversion function. Here is the actual workaround everyone is using, with fully working syntax:

select new SelectListItem { Value = SqlFunctions.StringConvert((double)store.ID), Text = store.Name };

To call this situation absurd is an understatement.

Solution 1

using LINQ query expression

 IEnumerable<SelectListItem> stores =
        from store in database.Stores
        where store.CompanyID == curCompany.ID
        select new SelectListItem { Value = store.Name, Text = store.ID };

 ViewBag.storeSelector = stores;

or using LINQ extension methods with lambda expressions

 IEnumerable<SelectListItem> stores = database.Stores
        .Where(store => store.CompanyID == curCompany.ID)
        .Select(store => new SelectListItem { Value = store.Name, Text = store.ID });

 ViewBag.storeSelector = stores;

Solution 2

Why not just use all Lambda syntax?

database.Stores.Where(s => s.CompanyID == curCompany.ID)
               .Select(s => new SelectListItem
                   {
                       Value = s.Name,
                       Text = s.ID
                   });

Solution 3

You appear to be trying to mix query expression syntax and "normal" lambda expression syntax. You can either use:

IEnumerable<SelectListItem> stores =
        from store in database.Stores
        where store.CompanyID == curCompany.ID
        select new SelectListItem { Value = store.Name, Text = store.ID};
ViewBag.storeSelector = stores;

Or:

IEnumerable<SelectListItem> stores = database.Stores
        .Where(store => store.CompanyID == curCompany.ID)
        .Select(s => new SelectListItem { Value = s.Name, Text = s.ID});
ViewBag.storeSelector = stores;

You can't mix the two like you're trying to.

Solution 4

Lambda Expression result

var storesList = context.Stores.Select(x => new { Value= x.name,Text= x.ID }).ToList();

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Comments

[Bill Software Engineer]

Can you please help me convert int to string? There seem to be no way for LINQ to Entity to convert int to string.

[Russ Cam]

@YongkeBillYu You mean like for example 5.ToString()?

[Russ Cam]

Can you create another question and show the code for what you are doing?

[Kgn-web]

@RussCam, if I am not wrong . Where(store => store.CompanyID == curCompany.ID) is of type Func<> lamda expression???

[Russ Cam]

@Kgn-web yes, a Func<T, bool> is passed to .Where(), where T is the type in IEnumerable<T>

[Kgn-web]

@RussCam. Thanks for your inputs. Irrespective of this question, can you please give me scenario where we use Action<> or Predicate<> lamda expression in LINQ. (You may use codepaste.net for sharing the snippet).

[Russ Cam]

@Kgn-web use Action<T> when you want to pass a delegate that doesn't return a value and Predicate<T> delegate where you need to return a boolean value; Predicate<T> was introduced in .NET 2.0, and generally Func<T, bool> is more often used, which was introduced in .NET 3.5 IIRC.

[Kgn-web]

@RussCam.Thanks mate :)