How do I display a list of objects in an Exception?

Question

I'm passing a List of Custom Objects to my Custom Exception Class and need to display all the objects in the message. How can I do this?

public class MissingUnitSNSException : Exception
{
    public MissingUnitSNSException()
    {

    }

    public MissingUnitSNSException(List<UnitViewModel> missingsns)
        : base(String.Format("Serial Numbers not found: {0}", missingsns))
    {

    }
}

The error tells me the type of object, but I need the serial number attribute that's tied to each object in the list.

Answer 1

How about replacing missingsns with a string of comma separated serial numbers. Like so:

string.join(", ", missingsns.Select(sns => sns.SerialNumber.ToString()))

This should list out the serial numbers like: A01, B01, C02, ...

---

Full line:

public MissingUnitSNSException(List<UnitViewModel> missingsns)
        : base(String.Format("Serial Numbers not found: {0}", 
                  string.join(", ", missingsns.Select(sns => sns.SerialNumber.ToString()))))

Answer 2

Please do not put important information into the message field. Getting them out there will be a pain for the user of your code!

Exceptions are classes. Add a readonly property for this data. Add it to what ToString() will return. This is one of the core rules of proper exception Handling:

• https://blogs.msdn.microsoft.com/ericlippert/2008/09/10/vexing-exceptions/
• https://www.codeproject.com/Articles/9538/Exception-Handling-Best-Practices-in-NET

Now with objects, you propably do not want to assign Reference to the Exception. Not only could the Exception keep the objects alive, there is a decent chance that Dispose is called on those instances before you get to process the Exception - making those references pretty useless.

As you seem content with "only" string data, a string[] might be a good type. You do have to mind to shallow clone it when handing it out, but otherwise it is normal readonly Property of Exceptions.