使用User.Identity.GetUserId的ASP MVC应用程序用户为空

Question

Ok so I have a relationship between the ApplicationUser and QuestionResults, my models are as below, the userId nor the UserName is retrieved, but I really need the UserId setup as a foreignKey on the QuestionResults entity.

Any help is much appreciated the error that I am receiving is as below:

An exception of type 'System.NullReferenceException' occurred in STRA.dll but was not handled in user code

Additional information: Object reference not set to an instance of an object.
on these lines of code:

qr.User.Id = User.Identity.GetUserId();
qr.User.UserName = User.Identity.GetUserName();

Models

public class QuestionResult
    {
        public QuestionResult()
        {
            DateCreated = DateTime.Now;
            DateModified = DateTime.Now;
        }
        public int Id { get; set; }
        public DateTime? DateCreated { get; set; }
        public DateTime? DateModified { get; set; }
        public int QuestionScore { get; set; }
        //navigation properties
        public virtual ApplicationUser User { get; set; }
        //public ICollection<CategoryResult> CategoryResult { get; set; }
        //public virtual Category Category { get; set; }
        [NotMapped]
        public int CategoryId { get; set; }
        public virtual Question Question { get; set; }
        public int QuestionId { get; set; }
        //public virtual Category Category { get; set; }
        //public int CategoryId { get; set; }
    }
public class ApplicationUser : IdentityUser
    {
        public string FirstName { get; set; }
        public string Surname { get; set; }
        public string Industry { get; set; }
        public string GlobalRegion { get; set; }
        public string CurrentSituation { get; set; }
        public int SalesForceSize { get; set; }
        public bool IsVerified { get; set; }
        //navigation properties
        public virtual ICollection<CategoryResult> CategoryResult { get; set; }
        public virtual ICollection<QuestionResult> QuestionResult { get; set; }
        //public virtual ICollection<Report> Report { get; set; }
        //public virtual ICollection<SurveyResult> SurveyResult { get; set; }
        public virtual Organisation Organisation { get; set; }
        public int? OrganisationId { get; set; }

        public async Task<ClaimsIdentity> GenerateUserIdentityAsync(UserManager<ApplicationUser> manager)
        {
            // Note the authenticationType must match the one defined in CookieAuthenticationOptions.AuthenticationType
            var userIdentity = await manager.CreateIdentityAsync(this, DefaultAuthenticationTypes.ApplicationCookie);
            // Add custom user claims here
            return userIdentity;
        }

    }

Answer 1

Your code is equivalent to this::

var user = qr.User;
user.Id = User.Identity.GetUserId();

If the QuestionResult was already linked to a User then you would not be changing which User is linked to the QuestionResult , you would be changing the Id of an existing User - and that is not allowed anyway.

But the QuestionResult is not already linked to a User . qr.User is null - so you get a null reference exception.

In general, life is much easier in Entity Framework if you add the foreign key to your model:

public class QuestionResult
{
   public string UserId { get; set; }

   public virtual ApplicationUser User { get; set; }
}

And now you can set the foreign key directly:

qr.UserId = User.Identity.GetUserId();

References:

Why does Entity Framework Reinsert Existing Objects into My Database?

Making Do with Absent Foreign Keys

Answer 2

So, do you wanna make foreing key for userid?

You can do like that:

    public int UserRefID { get; set; }
    [ForeignKey("UserRefID")]
    public xxx UserID { get; set; } //data name like ApplicationUser

And this error appear coz you have some problem about models or data classes.

Answer 3

Set it as a string

Model:

public ApplicationUser User { get; set; }
public string UserId { get; set; }

Controller:

qr.UserId = User.Identity.GetUserId();

And worked perfectly, even created foreign keys, that easy. Thanks so much!