The entity type Cargo is not part of the model for the curre

Question

Hello friends good morning, I have a problem with the Entity Framework more properly.

I have the following entity that comes from the db with entity framework

namespace CapaDatos
{
    using System;
    using System.Collections.Generic;

    public partial class tblCargo
    {
        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
        public tblCargo()
        {
            this.tblEmpleados = new HashSet<tblEmpleado>();
        }

        public int Id { get; set; }
        public string Nombre_Cargo { get; set; }

        [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
        public virtual ICollection<tblEmpleado> tblEmpleados { get; set; }
    }
}

As you will see the class is partial

this is why I create another file on the same layer called OperationsCargos

 Rename the class to tblCargo

namespace CapaDatos
{
    public partial class tblCargo
    {
        public static void Modificar(tblCargo tblCargo)
        {
            using (GourmetEntities db = new GourmetEntities())
            {
                try
                {
                    db.Entry(tblCargo).State = EntityState.Modified;
                    db.SaveChanges();
                }
                catch (Exception)
                {

                    throw;
                }
            }
        }
    }
}

this to have my methods in the same layer but in another file, that if I delete the entity my methods are lost

this is the btn code

private void TsbModificar_Click(object sender, EventArgs e)
        {
            objCargo.Id = int.Parse(TxtId.Text);
            objCargo.Nombre_Cargo = TxtCargo.Text;
            Cargo.Modificar(objCargo);
            MessageBox.Show("Registro con exito");

        }

when i run the application it shows me the following error

 

 

 

Please can you help me find my mistake,

Thanks a lot

Ro