如何在不使用 List 的情况下将 Linq 查询的值传递给普通字符串？

Question

A very simple question, yet I couldn't find the answer.

Let's say we have this:

    [HttpPost]
    public ActionResult Comparison(int id)
    {
        string makeLst = new List<String>();

        var makeQry = from m in db.Car
                      where m.ID == id
                      select m.Make;

        makeLst = makeQry.AddRange(makeQry);

        ViewBag.make = new List<String>(makeLst);
        return View();
    }

The "makeQry" Result View would be just one word (String). So I wanted to not use List for this, and just use String. Using ".ToString()" won't work since "makeQry.ToString()" would be the Query itself instead of the it's results. And I checked there is no method such as for instance makeQry.Result or something to get the result of Query.

Thank you.

Answer 1

You can use First() or FirstOrDefault() to get the single result:

ViewBag.make = makeQry.FirstOrDefault();

(The difference is that First throws an exception if the collection is empty, whereas FirstOrDefault just returns a null value in that case.)

Answer 2

Details: If you know for sure there will always be a matching value for ID then the below should do the job (not tested)

[HttpPost]
public ActionResult Comparison(int id)
{
   ViewBag.make = db.Car.FirstOrDefault(x => x.ID == id).Make;

   return View();
}

or if you prefer to keep the linq syntax how you are doing it

[HttpPost]
public ActionResult Comparison(int id)
{
   ViewBag.make = (from m in db.Car
                   where m.ID == id
                   select m.Make).FirstOrDefault();

   return View();
}

Answer 3

[HttpPost]
public ActionResult Comparison(int id)
{
    var makeQry = from m in db.Car
                  where m.ID == id
                  select m.Make;
    //As soon as the result is guaranteed to contain only one object 
    ViewBag.make = makeQry.SingleOrDefault();
    return View();
}

It uses Enumerable.SingleOrDefault Method (IEnumerable) , which returns the single element of the input sequence or null if there are no elements. It'll throw an exception, if the sequence contains more than one element.