mvc5中的c＃Linq查询返回的是列名而不是值

Question

I am doing an assignment using MVC5, I am trying to create a query using Linq which will return the logged in users "StudentId" from the "AspNetUsers" table. The code I have to try do this is,

string currentUser = User.Identity.GetUserId();
            string getStudentId = (from a in db.Users
                                   where a.Id.Equals(currentUser)
                                   select a.StudentId).ToString();

This is setting the string value to "StudentId;" which is the name of the column. (The ID is the default AspNetUsers table Data type which is nvarchar(128) ). Any help on where I am going wrong is much appreciated.

Answer 1

You'll need to execute the query first:

string getStudentId = (from a in db.Users
                               where a.Id.Equals(currentUser)
                               select a.StudentId).First().ToString();

Answer 2

One solution Might be

string currentUser = User.Identity.GetUserId();
string studentId;
studentId=db.Users.SingleOrDefault(o=>o.Id==currentUser).Select(o=>o.StudentId.ToString());

Answer 3

I tried your code with minor modifications below: (I substituted your StudentId column with my UserName column, and the viewbag shows the correct UserName on the view page)

        string currentUser = User.Identity.GetUserId();
        var getStudentId = (from a in db.Users
                               where a.Id.Equals(currentUser)
                               select a.UserName).FirstOrDefault().ToString();

        ViewBag.TestUser = getStudentId;

[ Update ]

I am assuming that your StudentId column is in your Users table.