OrderController.PutOrder.cs

// PUT: api/Order
[HttpPut]
public async Task<IActionResult> PutOrder([FromBody] Order order)
{
    // Apply changes to context
    _context.ApplyChanges(order);

    try
    {
        // Persist changes
        await _context.SaveChangesAsync();
    }
    catch (DbUpdateConcurrencyException)
    {
        if (!_context.Orders.Any(o => o.OrderId == order.OrderId))
            return NotFound();
        throw;
    }

    // Populate reference properties
    await _context.LoadRelatedEntitiesAsync(order);

    // Reset tracking state to unchanged
    _context.AcceptChanges(order);
    
    // Return updated order
    return Ok(order);
}