LINQ to SQL exception when attempting to insert a new entry in a database table

I'm trying to insert a user in my database via LINK to SQL a开发者_如何学Gond I'm getting an exception:

Cannot insert the value NULL into column 'UserID', table 'mydatabase.developer.Users'; column does not allow nulls. INSERT fails. The statement has been terminated.

I've marked the UserID as the primary key in my Users table and I was expecting that the SQL Server will automatically generate a PK when I try to insert a new user in the table.

I pretty much copied and pasted the example from Pro ASP.NET MVC Framework Chapter 4 Section on "Setting Up LINQ to SQL." Everything is in order... my database has a Users table with a UserID (PK) column and a Name column (both non-nullable), below is the class corresponding to the database table:

public class User
{
    [DisplayName("User ID")]
    [Column(IsPrimaryKey=true, IsDbGenerated=true, AutoSync=AutoSync.OnInsert)]
    internal int UserID { get; set; }

    [DisplayName("Name")]
    [Column]
    public string Name{ get; set; }
}

I also have a repository class which allows me to modify the database:

public class UsersRepository : IUsersRepository
{
    private DataContext database;
    private Table<User> usersTable;

    public UsersRepository(string connectionString)
    {
        database = new DataContext(connectionString);
        usersTable = database.GetTable<User>();
    }

    public void AddUser(User user)
    {
        usersTable.InsertOnSubmit(user);
        try
        {
            database.SubmitChanges();
        }
        catch (Exception e)
        {
            var msg = e.Message;
        }
    }
    //...
}

IUsersRepository ur = new UsersRepository(connectionString);
ur.AddUser(new User{Name = "Joe"});

I've also tried setting the UserID to -1, 0 and 1, but I get the same exception!

ur.AddUser(new User{UserID = -1, Name = "Joe"});
ur.AddUser(new User{UserID = 0, Name = "Joe"});
ur.AddUser(new User{UserID = 1, Name = "Joe"});

Does anybody know what may be happening here? I'm really baffled by this: what could cause the SQL server not generating the primary key? Is there any way I can inspect the insert statement and verify what is actually being sent to the server?

Is your primary key an integer? You need to set the identity specification:

If you are using something like a uniqueidentifier, you need to generate on the client with

User user = new User();

user.Id = Guid.NewGuid();

Check the properties of the table and make sure UserId allow nulls is set to false; make sure auto-increment is set to yes