C# 加入列表<of type>和处理 NULL/Empty 值

Question

I have 2 lists that I am joining. List 1 contains all IP's in a subnet and list 2 contains assigned IP's.

Both these lists are of the same structure. example below (removed extra fields):

int IPAddress
int AssingmentType

In list 1, "AssingmentType" will always be empty, but in list 2, both fields will be populated, but only a for assigned IP's. I would like to generate a full IP listing, and joing it with List 2, showingwhen an IP is assigned.

I'm using LINQ for this and have the following so far

            var results = from t1 in allIPinNetwork
                      join t2 in assignedIPs on t1.IPAddressText equals t2.IPAddressText into combinedIP
                      from t3 in combinedIP.DefaultIfEmpty()
                      select new IPAddress()
                      {
                          IpAddressText = t1.IpAddressText,
                          AssingmentType = t3 == null ? 0 : t3.AssingmentType,

                      };

My querie is, how best do I handle the "null" values that are for AssingmentType? In this case I've set them to 0, but is there a null value I can use to leave them blank? In the full class there will also be some string fields that could be blank.

Happy if anyone has a better way to do this?

Thanks

Answer 1

Both these lists are of the same structure.

Well, that is the problem right there, they dont seem to have the structure you believe they do. If the lists can have empty AssignmentType fields, then AssignmentType can not be of type int ; int must always be a value.

What you probably want is that both lists have the following structure:

int IPAddress
int? AssignmentType

And, yes, when AssignmentType is not set, it should be null .

Another option could be changing AssignmentType to an enumeration:

enum IPAssignmentType
{
     NotAssigned,
     Dynamic,
     Static,
     //whatever
}

My last option would be using -1 as unassgined value but thats just yuck if avoidable (its essentially the same as enumeration but uglier and less mantainable).