Entity framework many-to-many IEntityChangeTracker error. How to solve?

Question

Entity framework many-to-many IEntityChangeTracker error. How to solve?

Navigation

#1 by (1 votes)

2

I have a many-to-many relationship and my tables are correct about the relationship in the database. The problem is that my insert works perfectly when you do not use an existing entity in the database, but when I search the database and add it again it understands that I am not only "referencing" but adding a new entity. >

entity news:

[Table("Noticia")]
public class
{
    [Key]
    public Guid Id { get; set; }

    [Required]
    [MaxLength(50)]
    public string Titulo { get; set; }

    #region Relationships
    public virtual ICollection<Tag> Tags { get; set; }
    #endregion Relationships
}

Tag model:

[Table("Tag")]
public class Tag
{
    [Key]
    [Required]
    [MinLength(3), MaxLength(30)]
    public string Descricao { get; set; }

    #region Relationships
    [Required]
    public virtual ICollection<Noticia> Noticias { get; set; }        
    #endregion Relationships
}

this relationship (ICollection

Controller:

[HttpPost, ValidateAntiForgeryToken]
    public ActionResult Create(NoticiaViewModel vModel)
    {
         if (vModel != null && vModel.ArquivoImagem != null && vModel.ArquivoImagem.ContentLength > 0)
         {
              vModel.Id = Guid.NewGuid();
              vModel.DataPostagem = DateTime.Now;
              vModel.Tags = ObterTags(vModel.TagsEmLinha, vModel.Id);
              vModel.UsuarioId = User.ToAvatarPrincipal().AvatarIdentity.Id;
              vModel.Imagem = new Imagem
              {
                  Id = Guid.NewGuid(),
                  CaminhoImagem = FileUploaderHelper.Upload(vModel.ArquivoImagem, User.ToAvatarPrincipal().AvatarIdentity.TipoUsuario,vModel.Id.ToString())
              };

              if (ModelState.IsValid)
              {
                  ///TODO: Quando a tag já foi utilizada, esta dando erro de primary key já existente na Tag.
                  if (_noticiaService.Gravar(ModelBuilderHelper.BuildNoticia(vModel)))
                  return RedirectToAction("List");
              }
        }
                return View(vModel);
   }

   private List<Tag> ObterTags(string tagsEmLinha)
   {
        if (!string.IsNullOrEmpty(tagsEmLinha))
        {
             Tag tagFromDb = null;
             var tags = new List<Tag>();
             if (tagsEmLinha.Contains(","))
             {
                  foreach (var tagDescricao in tagsEmLinha.Split(','))
                  {
                       tagFromDb = DefineTag(tags, tagDescricao);
                  }
             }
             else
             {
                  tagFromDb = DefineTag(tags, tagsEmLinha);
             }
             return tags;
        }
        return null;
   }

   private Tag DefineTag(List<Tag> tags, string tagDescricao)
   {
        Tag tagFromDb = _tagService.ObterPor(tagDescricao);
        if (tagFromDb != null)
            tags.Add(tagFromDb);
        else
        {
            tags.Add(new Tag
            {
                 Descricao = tagDescricao
            });
        }

        return tagFromDb;
   }

Remembering that by adding a non-existent news item with a nonexistent tag, it inserts all the tags correctly (insert news, tag and tagNoticia). But if I insert news for a tag that already exists (make the many-to-many relationship), the error occurs:

Error:

An entity object can not be referenced by multiple instances of IEntityChangeTracker.

c# entity-framework asp.net-mvc code-first

asked by anonymous 26.02.2016 / 03:57

1 answer

How do I limit the rotation of 2-axis prefabs in Unity? How to use the ob_flush () function to return data to browser animatedly?

score 1 · Answer 1

I changed my Service to the following:

public bool GravarNoticia(Noticia noticia, List<string> tags)
{
    Noticia novaNoticia = null;

    using (_noticiaRepository)
    {
        try
        {
            novaNoticia = new Noticia
            {
                DataPostagem = noticia.DataPostagem,
                Descricao = noticia.Descricao,
                Id = noticia.Id,
                Imagem = noticia.Imagem,
                Titulo = noticia.Titulo,
                UsuarioId = noticia.UsuarioId,
                Tags = new List<Tag>()
            };

            foreach (var tag in tags)
            {
                var tagFromDb = _noticiaRepository.ObterTag(tag);

                if (tagFromDb != null)
                    novaNoticia.Tags.Add(tagFromDb);
                else
                    novaNoticia.Tags.Add(new Tag
                    {
                        Descricao = tag,
                        Id = Guid.NewGuid()
                    });
            }

            return Gravar(novaNoticia);
        }
        catch (System.Exception)
        {
            throw;
        }
    }
}

What happened was that I used two different instances of my context, one in the search and the other in the insert, that's where the conflict happened, because the Entity Framework did not understand that it was the same entity and tried to insert again over a nonexistent one.

official link from where I was based to get the answer: link