Our current O/RM tool does not really allow for rich domain models, so we are forced to utilize anemic (DTO) entities everywhere. This has worked fine, but I continue to struggle with where to put basic object-based business logic and calculated fields.

Current layers:

• Presentation
• Service
• Repository
• Data/Entity

Our repository layer has most of the basic fetch/validate/save logic, although the service layer does a lot of the more complex validation & saving (since save operations also do logging, checking of permissions, etc). The problem is where to put code like this:

Decimal CalculateTotal(LineItemEntity li)
{
  return li.Quantity * li.Price;
}

or

Decimal CalculateOrderTotal(OrderEntity order)
{
  Decimal orderTotal = 0;
  foreach (LineItemEntity li in order.LineItems)
  {
    orderTotal += CalculateTotal(li);
  }
  return orderTotal;
}

Any thoughts?