附加實體中的錯誤

Question

我在從Entity框架中的模型集合中嘗試項目時遇到此錯誤。我得到以下錯誤：

Attaching an entity of type '' failed because another entity of the same type already has the same primary key value. This can happen when using the 'Attach' method or setting the state of an entity to 'Unchanged' or 'Modified' if any entities in the graph have conflicting key values. This may be because some entities are new and have not yet received database-generated key values. In this case use the 'Add' method or the 'Added' entity state to track the graph and then set the state of non-new entities to 'Unchanged' or 'Modified' as appropriate

請能有人幫忙我堅持 這裏是我的代碼：

public class Attendees 
{ 
    [Key] 
    public int AttendeesId { get; set; } 
    public ICollection<Programme> programmes { get; set; } 
    public ICollection<Presentations> presentations { get; set; } 
    public ICollection<Abstracts> abstracts { get; set; } 
    [Required] 
    public bool IsKeynoteSpeaker { get; set; } 



    } 
public class Programme 
{ 
    [Key] 
    public int ProgrammeId { get; set; } 
    [Required, MaxLength(256, 
     ErrorMessage = "The length of the field is more than expected")] 
    public string Title { get; set; } 
    public ICollection<Attendees> presenters { get; set; } 
    public ICollection<Attendees> chairpersons { get; set; } 
    public ProgrammeType programmeType { get; set; } 
    public ConferenceDay Daynumber { get; set; } 


} 

public void RemovePresenterFromProgramme(Programme programme,Attendees  attendees) 
    { 
     var context = _programmeRepository.GetGenericRepository.GetDbContext as ConferenceDbContext; 

     context.Entry(programme).State = System.Data.Entity.EntityState.Modified; // get the error here 
     var attendee = programme.presenters 
      .Where(c => c.AttendeesId == attendees.AttendeesId).SingleOrDefault(); 

     programme.presenters.Remove(attendee); 
     context.SaveChanges(); 
    } 

Answer 1

謝謝Junnas，但我發現在這附近。由於Program對象具有已經存在於上下文中的導航屬性，因此拋出了錯誤。這導致它不附加，所以這是我做了什麼來解決它。

var context = _programmeRepository.GetGenericRepository.GetDbContext as ConferenceDbContext; 
context.Entry(attendees).State = System.Data.Entity.EntityState.Detached; 
context.ProgrammeObjects.Attach(programme); 
var attendee = programme.presenters 
      .Where(c => c.AttendeesId == attendees.AttendeesId).SingleOrDefault(); 
programme.presenters.Remove(attendee); 

context.Entry(programme).State = System.Data.Entity.EntityState.Modified; 

context.SaveChanges(); 

Program對象已經有一個存在於上下文中的與會者對象。所以不得不告訴entityframework，通過分離它並停止跟蹤所述與會者對象併爲我工作。儘管感謝您的幫助。

Answer 2

能否請您嘗試這樣的事情？

context.Programmes.Attach(programme); 
var entry = context.Entry(programme); 
entry.State = EntityState.Modified; 
var attendee = programme.presenters 
      .Where(c => c.AttendeesId == attendees.AttendeesId).SingleOrDefault(); 

     programme.presenters.Remove(attendee); 
context.SaveChanges();