@Override
 public int hashCode() {
   final int prime = 31;
   int result = 1;
   result = prime * result + ((fecha == null) ? 0 : fecha.hashCode());
   result = prime * result + idOrdenDeCompra;
   result = prime * result + ((items == null) ? 0 : items.hashCode());
   result = prime * result + ((proveedor == null) ? 0 : proveedor.hashCode());
   return result;
 }
 @Override
 public boolean equals(Object obj) {
   if (this == obj) return true;
   if (obj == null) return false;
   if (getClass() != obj.getClass()) return false;
   OrdenDeCompra other = (OrdenDeCompra) obj;
   if (fecha == null) {
     if (other.fecha != null) return false;
   } else if (!fecha.equals(other.fecha)) return false;
   if (idOrdenDeCompra != other.idOrdenDeCompra) return false;
   if (items == null) {
     if (other.items != null) return false;
   } else if (!items.equals(other.items)) return false;
   if (proveedor == null) {
     if (other.proveedor != null) return false;
   } else if (!proveedor.equals(other.proveedor)) return false;
   return true;
 }