How to load data to an ASP.NET MVC table from related tables

In principle, your code should work correctly, but there are a series of considerations that you do not indicate in your question, which may be the ones that are causing the error.

The first and most obvious is that the MyTablaCamposand properties MyTablaUsersof the class MyModelare not returning any value. Check this with the debugger before returning the results to the View from the Controller.

The second option is that you are not returning the Model correctly from the Controller to the View. You should have stated your Controller code in the question. Note that your View must receive a Model of type MyModel, and you must indicate this with the directive @model List<MyModel>. On the other hand, from the Controller you must send the Model with the data to represent to the View.

I have reproduced your example in Visual Studio, and with the Controller that I indicate below it works correctly:

    public class HomeController : Controller
{
    public IActionResult Index()
    {
        List<MyModel> myModels = new List<MyModel>();

        MyModel myModel_1 = new MyModel()
        {
            Id = 1,
            Codigo_User = "1",
            Fecha_solicitud = DateTime.UtcNow.AddHours(1),
            Codigo_Campo = null,
            Ubicacion = "ubicación1",
            Campos = new MyTablaCampos()
            {                    
            },
            Users = new MyTablaUsers() {
                Codigo_User = "1",
                Nombre = "User 1"
            }                
        };

        MyModel myModel_2 = new MyModel()
        {
            Id = 2,
            Codigo_User = "2",
            Fecha_solicitud = DateTime.UtcNow.AddHours(2),
            Codigo_Campo = 2,
            Ubicacion = "ubicación2",
            Campos = new MyTablaCampos()
            {
                Codigo_Campo = 2,
                Descripcion = "Campo 2"
            },
            Users = new MyTablaUsers()
            {
                Codigo_User = "2",
                Nombre = "User 2"
            }
        };

        MyModel myModel_3 = new MyModel()
        {
            Id = 3,
            Codigo_User = "3",
            Fecha_solicitud = DateTime.UtcNow.AddHours(3),
            Codigo_Campo = 3,
            Ubicacion = "ubicación3",
            Campos = new MyTablaCampos()
            {
                Codigo_Campo = 3,
                Descripcion = "Campo 3"
            },
            Users = new MyTablaUsers()
            {
                Codigo_User = "3",
                Nombre = "User 3"
            }
        };

        myModels.Add(myModel_1);
        myModels.Add(myModel_2);
        myModels.Add(myModel_3);

        return View(myModels);
    }

}

The problem has to be in the way the three tables in your example are related. The table MyTablaCamposalso has a relationship with the table MyTablaUsersthrough the field public string Codigo_User { get; set; }.

When you perform the LinQ query from s in bd.MyModel select s, the condition that is translated to SQL would be:

WHERE MyModel.Codigo_User = MyTablaUsers.Codigo_User AND 
      MyModel.Codigo_User = MyTablaCampos.Codigo_User

Try modifying the Model MyTablaCamposand adding the property to it public MyTablaUsers Users { get; set; }:

public partial class MyTablaCampos
{
    public short Cod_Empresa { get; set; }
    public string Codigo_User { get; set; }        
    public short Codigo_Campo { get; set; }
    public string Descripcion { get; set; }
    public short Tipo { get; set; }
    public short Producto { get; set; }
    public MyTablaUsers Users { get; set; } 
}

What you could do is create a ModelView to be able to execute what you are proposing.

public partial class MyModelView
    {
        public MyModel Model { get; set; }
        public MyTablaCampos Campos { get; set; }
        public MyTablaUsers Users { get; set; }
        public List<MyTablaCampos> CamposLST { get; set; } // Solo en caso de que puedas tener mas de un MyTabla en un solo Model
        public List<MyTablaUsers> UsersLST { get; set; } // Solo en caso de que puedas tener mas de un MyTablaUsersen un solo Model
    }

In your controller:

public ActionResult SetSolicitud()
{
 var item = from s in bd.MyModel select s;
 return View(item.ToList());
}

I'll replace it with a lambda expression:

public ActionResult SetSolicitud()
{
 var model = bd.MyModel.Include(x => x.Users).Include(y => y.Campos).ToList();
 return View(model);
}

According to the official documentation :

Loading diligently (eagerly loading)

Eager loading is the process by which a query for one entity type also loads related entities as part of the query. Eager loading is achieved by using the include method. For example, the following queries will load blogs and all posts related to each blog.

Documentation note:

Include is an extension method on the namespace System. Data. Entity, so you need to make sure you're using that namespace.

Comment:

Now in theory you already have the property loaded and it should be available to be rendered by the view.

Update:

public partial class MyModel
    {
        public int Id { get; set; }
        public string Codigo_User { get; set; }
        [DisplayFormat(DataFormatString = "{0:dd/MM/yyyy}", ApplyFormatInEditMode = true)]
        public Nullable<System.DateTime> Fecha_solicitud { get; set; }
        public Nullable<int> Codigo_Campo { get; set; }
        public string Ubicacion { get; set; }       
        //Aqui la navegación entre clases:
        public virtual MyTablaCampos Campos { get; set; } 
        public virtual MyTablaUsers Users { get; set; }
    }

In the class to which it is related:

 public partial class MyTablaUsers 
        {
            public string Codigo_User { get; set; }
            public string Nombre { get; set; }
            public string Contacto { get; set; }
            public string RFC { get; set; }
            //Con esto Entity Framework entiende la relación:
            public virtual MyModel mymodel { get; set; }
        }

Now regarding the fields:

 public partial class MyTablaCampos 
    {
        public short Cod_Empresa { get; set; }
        public string Codigo_User { get; set; }
        public short Codigo_Campo { get; set; }
        public string Descripcion { get; set; }
        public short Tipo { get; set; }
        public short Producto { get; set; }
        //Con esto Entity Framework entiende la relación:
        public virtual MyModel mymodel { get; set; }
      }

To improve your understanding and mastery of the Entity Framework, this site is highly recommended: https://www.entityframeworktutorial.net/