C＃Linq-to-SQL多列

Question

I am currently trying to select multiple columns in C# with Linq-to-SQL. When looking at other threads just as this one it is a pretty simple thing to do, so I tried:

var users = context.GetTable<DbHelper.User>();

var query = from u in users
            where u.Email == TbUsername.Text
            select new { u.Active, u.Password };

if(!query.Any())
{
  MessageBox.Show("Could not find an account with that Email");
  return;
}

var result = query.First();   // Error occurs here

User table in DbHelper :

[Table(Name="Users")]
public class User 
{
    [Column(IsPrimaryKey = true, AutoSync = AutoSync.OnInsert, IsDbGenerated = true)]
    public int Id { get; set; }

    [Column]
    public int RoleID { get; set; }

    [Column]
    public string Email { get; set; }

    [Column]
    public string Password { get; set; }

    [Column]
    public string Firstname { get; set; }

    [Column]
    public string Lastname { get; set; }

    [Column]
    public int OfficeID { get; set; }

    [Column]
    public string Birthdate { get; set; }

    [Column]
    public int Active { get; set; }
}

The table looks like this in SQL Server:

[ID]        INT           IDENTITY (1, 1) NOT NULL,
[RoleID]    INT           NOT NULL,
[Email]     NVARCHAR(150) NOT NULL,
[Password]  NVARCHAR(50)  NOT NULL,
[FirstName] NVARCHAR(50)  NULL,
[LastName]  NVARCHAR(50)  NOT NULL,
[OfficeID]  INT           NULL,
[Birthdate] DATE          NULL,
[Active]    BIT           NULL,

Which results in an error

System.InvalidCastException: The conversion is invalid

What is wrong with my code? It's really confusing since it seems to work for others. If you need more code please let me know

Answer 1

Try to use .FirstOrDefault() :

var result = query.FirstOrDefault();

If the result is null after this call, then your selection just didn't return any rows from the database table.

Answer 2

As the type of the Active column in your database table is 'bit', EF expects a property of type 'bool'. 0==false, 1==true, as you might expect.