EntityFramework正在插入新的寄存器，而不是设置关系的ID

Question

I'm developing a website that allows the users Post issues.

I have 3 tables:

• Post;
  • PostId;
  • UserId;
• City;
  • CityId;
  • CityName;
• PostService (a composite table);
  • PostId (Related to Post);
  • CityId (Related to City);
  • Other Fields;

When I save the Post the system inserts a new Post, do the relationship between PostService and Post (by the PostId), but, it should set the CityId in to PostService, but, instead, it creates a new City, and do the relationship to the PostService.

Here, we set the selected City into the PostService:

orcamento.Cidades = db.Cidades.Where(c => c.CidNome.Trim().ToLower() == orcamento.Cidades.CidNome.Trim().ToLower()).FirstOrDefault();

and here, we persist the Post:

Post post = new Post();
post.PosData = DateTime.Now;
post.Usuarios = db.Usuarios.Where(u => u.UsuEmail == User.Identity.Name).FirstOrDefault();
post.PostOrcamentoServico.Add(orcamento);
db.Post.Add(post);
db.SaveChanges();

Why it is creating a new City instead set the CityID to PostService?

Answer 1

To fix that, use the same Transaction of the Context.

The following code were in another Context

orcamento.Cidades = db.Cidades.Where(c => c.CidNome.Trim().ToLower() == orcamento.Cidades.CidNome.Trim().ToLower()).FirstOrDefault();