异常实体已被跟踪

Question

I'm getting an error for tracking the sane model but I don't know how else to access the model and save the changes. The error reads like this:

        System.InvalidOperationException: 'The instance of entity type 'UserMetaData' cannot be tracked 
    because another instance with the same key value for {'UserId'} is already being tracked. When attaching
     existing entities, ensure that only one entity instance with a given key value is attached. Consider 
    using 'DbContextOptionsBuilder.EnableSensitiveDataLogging' to see the conflicting key values.'

The code that is crashing my site is this:

public IActionResult ConsentForm(string holder)
{
    var id = _httpContextAccessor.HttpContext.Session.GetString("UserId");
    var userId = new Guid(id);
    var userMetaInfo = _elearnContext.UserMetaData.Where(u => u.UserId == userId).SingleOrDefault();


    UserMetaData userMetaData = new UserMetaData
    {
        UserId = userId,
        Consent = userMetaInfo.Consent,
        Location = "",
        CanChangePassword = true
    };
    _elearnContext.UserMetaData.Add(userMetaData);// crashes here 
    _elearnContext.SaveChanges();
    return RedirectToAction("LogOn", "Account");
    // return View("~/Views/Home/ConsentForm.cshtml", ConsentData);
}

I think the problem is that before I call this function I am using the same access in the former function like this:

public IActionResult RedirectToConsentForm(string controllerName, string actionName)
{

    var Id = _httpContextAccessor.HttpContext.Session.GetString("UserId");
    var UserId = new Guid(Id);
    var UserMetaInfo = _elearnContext.UserMetaData.Where(u => u.UserId == UserId).SingleOrDefault();


    if (UserMetaInfo.Consent == true)
    {
        return RedirectToAction("ConsentForm", "Account");

    }
    else
    {
        return RedirectToAction(controllerName, actionName);
    }

}

If any one has any ideas please let me know.

Answer 1

Your scenario in this case is actually update the metadata if existed otherwise add a new one. It crashes because after querying for the metadata, it's tracked ( AsNoTracking is not used). Then that tracked entity is added to the context and causes the error. Here's how it should be:

var userMetaInfo = _elearnContext.UserMetaData.SingleOrDefault(u => u.UserId == userId) ?? new UserMetaData();
if(userMetaInfo.UserId == 0){
  //set the consent only at the time creating a new metadata
  userMetaInfo.Location = someLocation;
  userMetaInfo.CanChangePassword = true;
  //add the new entity to the context (mark it as added)
  _elearnContext.UserMetaData.Add(userMetaInfo);
}
//now set this to update the consent which should be true
//because this code is run only after the user accepted (redirected from another action)
userMetaInfo.Consent = true;

//finally save the changes
_elearnContext.SaveChanges();

Note I'm not sure about what you set for the Location (and when to update it). So it depends on your logic. But it looks like in the code above the only thing you want to update is the Consent property and it must be true . Although we check for the UserId to know if it's being creating a new metadata but I believe that at that time, the metadata may already have been created (somewhere else). However it's the general logic we process it in this case (something like adding the entity only if there is no existing data, otherwise update the properties on the fetched and tracked entity).