通过使用 EF 插入数据库对多个实例的实体引用

Question

我将使用 Entity Framework 和 ASP.NET MVC 应用程序将博客插入到我的数据库中。如果我想将实体添加到上下文中，我在下面代码的最后一行遇到了这个错误。

InvalidOperationException: An entity object cannot be referenced by multiple instances of IEntityChangeTracker.

这是我的代码：

public class AdminController : Controller
{
    [HttpPost]
    public ActionResult CreateBlog(BlogViewModel vm)
    {
        try
        {
            _blogService.Insert(new Blog()
            {
               Titel = vm.Titel,
               Beschrijving = vm.Beschrijving,
               Content = (vm.Actie.ToLower() == "publiceer" ? true : false),
               Verwijderd = false,
               Auteur = UserManager.FindById(User.Identity.GetUserId())
           });
        }
        catch (Exception ex)
        {
            Console.Write(ex.Message);
        }

        return RedirectToAction(nameof(Blog));
    }

    public ApplicationUserManager UserManager
    {
        get
        {
            return _userManager ?? HttpContext.GetOwinContext().GetUserManager<ApplicationUserManager>();
        }
        private set
        {
            _userManager = value;
        }
    }

    public AdminController(ApplicationUserManager userManager, IBlogService blog)
    {
        UserManager = userManager;
        _blogService = blog;
    }
}

public class BlogService : IBlogService
{
    public void Insert(Blog blog)
    {
        _blogRepo.Insert(blog);
        _blogRepo.SaveChanges();
    }
}

public class BlogRepo : GenericRepo<Blog>
{
    public override Blog Insert(Blog blog)
    {
        context.Entry(blog.Auteur).State = EntityState.Unchanged;
        return dbSet.Add(blog); // --> on this line
    }
}

你能找到我做的问题吗？提前致谢。

Answer 1

我想你的实体模型看起来像：

public class Blog
{
    [Key]
    public int Id { get; set; }

    [Required]
    // etc
    public string Titel { get; set; }

    public string Beschrijving { get; set; }

    public bool Content { get; set; }

    public bool Verwijderd { get; set; }

    public ApplicationUser Auteur { get; set; }
}

为什么不直接将 AuteurId 属性添加到您的实体 class。通过这种方式，您将避免在获取用户实体 (UserManager.FindById(User.Identity.GetUserId())).

时进行额外查询

public class Blog
{
    [Key]
    public int Id { get; set; }

    [Required]
    // etc
    public string Titel { get; set; }

    public string Beschrijving { get; set; }

    public bool Content { get; set; }

    public bool Verwijderd { get; set; }

    [ForeignKey("Auteur")]
    public string AuteurId { get; set; }

    public virtual ApplicationUser Auteur { get; set; }
}

然后在您的操作代码中将像

_blogService.Insert(new Blog()
{
   Titel = vm.Titel,
   Beschrijving = vm.Beschrijving,
   Content = (vm.Actie.ToLower() == "publiceer" ? true : false),
   Verwijderd = false,
   AuteurId = User.Identity.GetUserId()
});

通过使用 EF 插入数据库对多个实例的实体引用

entity referenced to multiple instances by instert into the database with EF

c#

asp.net-mvc

entity-framework

invalidoperationexception