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

Answer 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;

Answer 2

Using Lambda expressions:

1. If we don't have a specific class to bind the result:

    var stores = context.Stores.Select(x => new { x.id, x.name, x.city }).ToList();
   

2. If we have a specific class then we need to bind the result with it:

   List<SelectListItem> stores = context.Stores.Select(x => new SelectListItem { Id = x.id, Name = x.name, City = x.city }).ToList();
   

Using simple LINQ expressions:

1. If we don't have a specific class to bind the result:

   var stores = (from a in context.Stores select new { x.id, x.name, x.city }).ToList();
   

2. If we have a specific class then we need to bind the result with it:

   List<SelectListItem> stores = (from a in context.Stores select new SelectListItem{ Id = x.id, Name = x.name, City = x.city }).ToList();
   

Answer 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.

Answer 4

Lambda Expression result

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

Answer 5

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
                   });