modify a field of ten that I have in the table with entity f

Question

Very good day. I have a table to which I only want to modify the image in a field

 

 

 

I just need to change the image field, for this I do the following

public partial class tblProducto {
 [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")]
 public tblProducto() {
  this.tblDetalleVentas = new HashSet < tblDetalleVenta > ();
  this.tblKardexes = new HashSet < tblKardex > ();
  this.tblDetalleIngresoProductos = new HashSet < tblDetalleIngresoProducto > ();
 }

 public int Id {
  get;
  set;
 }
 public int Categoria_Id {
  get;
  set;
 }
 public int UnidadMedida_Id {
  get;
  set;
 }
 public string Codigo {
  get;
  set;
 }
 public string ProductoDescripcion {
  get;
  set;
 }
 public Nullable < decimal > PrecioVenta {
  get;
  set;
 }
 public Nullable < decimal > Stock {
  get;
  set;
 }
 public System.DateTime FechaCreado {
  get;
  set;
 }
 public string NombreImagen {
  get;
  set;
 }
 public byte[] Imagen {
  get;
  set;
 }
 public int Estado_Id {
  get;
  set;
 }
 public int Usuario_Id {
  get;
  set;
 }

 public virtual tblCategoria tblCategoria {
  get;
  set;
 }
 [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
 public virtual ICollection < tblDetalleVenta > tblDetalleVentas {
  get;
  set;
 }
 public virtual tblEstado tblEstado {
  get;
  set;
 }
 [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
 public virtual ICollection < tblKardex > tblKardexes {
  get;
  set;
 }
 public virtual tblUnidade tblUnidade {
  get;
  set;
 }
 public virtual tblUsuario tblUsuario {
  get;
  set;
 }
 [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")]
 public virtual ICollection < tblDetalleIngresoProducto > tblDetalleIngresoProductos {
  get;
  set;
 }
}

I have the following method

public static void ModificarImagen(tblProducto objProducto)
{
    using (GourmetEntities db = new GourmetEntities())
    {
        db.tblProductos.Attach(objProducto);
        db.Entry(objProducto).Property(x => x.Imagen).IsModified = true;
        db.SaveChanges();
    }
}

in the button event I have the following code

private void BtnModificar_Click(object sender, EventArgs e) {
 //try
 //{
 byte[] Imagen = null;
 Stream myStream = openFileDialog1.OpenFile();
 using(MemoryStream ms = new MemoryStream()) {
  myStream.CopyTo(ms);
  Imagen = ms.ToArray();
 }
 foreach(var item in ListaProductos) {

  ObjProducto.Imagen = Imagen;
 }
 tblProducto.ModificarImagen(ObjProducto);
 //ObjProducto.Id = IdProducto;
 //ObjProducto. = "NO CAMBIAR";
 //ObjProducto.Estado_Id = 0;
 //ObjProducto.Imagen = Imagen;

 //    MessageBox.Show("Datos modificados correctamente", "INFORMACIÓN DEL SISTEMA", MessageBoxButtons.OK, MessageBoxIcon.Information, MessageBoxDefaultButton.Button1);
 //}
 //catch (Exception ex)
 //{

 //    MessageBox.Show("Ocurrio un problema, los datos no se modificaron", "INFORMACIÓN DEL SISTEMA", MessageBoxButtons.OK, MessageBoxIcon.Error, MessageBoxDefaultButton.Button1);
 //}
}

but I get the following error,

 

 

 

it tells me that all the fields are mandatory. How can I solve this problem if you please, since there are 1000 fields, I must write the thousand fields. please help with this problem for me

 

RM.