Single field extraction from a database using lambda

My problem is connected to the extraction method called lambda ( I am using it in C# ). I have a database and in it I have a table called Students and I wonder if I would be able to extract the firstName and lastName of certain student whose ID matches my search.

I have tried a few things so far without any luck.

A bit of code from my last attempt : 

var studentName =
    context.Student //context is the variable with the entities and Student is the table
    .Where(student => student.StudentID == SomeInt) // extract only the one with the chosen ID
    .Select(student => student.FirstName) // tryng only to select the wanted field(s)
    .ToString() // since I want it to be displayed in a textbox
Jon Skeet
people
quotationmark

Currently you're calling Select on an IQueryable<string> - your query represents a sequence of student first names, even if it only matches a single one.

If you only want a single name, you can use:

var studentName =
    context.Student
           .Where(student => student.StudentID == SomeInt)
           .Select(student => student.FirstName)
           .FirstOrDefault();

Then assuming FirstName is a string, you don't need ToString() at all. The value will be null if there's no student with that ID. Alternatively, you could use Single(), SingleOrDefault(), First(), Last() or LastOrDefault(). So for example, you'd then use:

if (studentName == null)
{
    // No match found. Return an error or whatever.
}
else
{
    // Use studentName
}

(You should only use FirstOrDefault() if you then check for nullity, or pass it on to something else that does so. Otherwise you can end up with a NullReferenceException later which is hard to diagnose.)

If you want both the first and last names, you need to change your projection. For example:

var studentName =
    context.Student
           .Where(student => student.StudentID == SomeInt)
           .Select(student => new { student.FirstName, student.LastName })
           .FirstOrDefault();

Now the type of studentName will be an anonymous type - again, it'll be null if there are no matches, but otherwise it will have appropriate FirstName and LastName properties.

people

See more on this question at Stackoverflow