How can I change this code in C # so that Visual Studio recognizes that I am not an idiot?

It seems like you are iterating through the collection trying to find one matching value based on the organization name. You can use LINQ SingleOrDefault()

to find (at most) one match:

var selectedOrg = PD.orgs.SingleOrDefault(o => o.orgname == selectedOrgName);

      

        
        
        
      

    

Then only called InsertOnSubmit()

if the value found is: (otherwise selected Org will be null)

if (selectedOrg != null)
    PD.cats.InsertOnSubmit(new Category { orgid = selectedOrg.orgid, catname = newCatName });

      

        
        
        
      

    

Edit: The OP modified the question to indicate that only one item will be found and no multiple solution is required, here is Option 1a

Option 1a - One Linq Method

This provides a linq one line query that filters out unneeded organizations, grabs one item, and selects a new category object to be used as a parameter for your insert. This method will throw an exception if a single element cannot be located, but that is clearly what should happen depending on your question.

PD.cats.InsertOnSubmit(
    PD.orgs.Where(o=>o.orgname==selectedOrgName)
    .Single()
    .Select(o=>new Category { orgid = o.orgId, catname = newCatName })
);

      

        
        
        
      

    

Option 1b - Iterate the filtered list and get the job done

All other answers here suggest using linq and assume that only one entry will be found. Why not just do everything in a loop and use linq to filter the results?

foreach (Organization o in PD.orgs.Where(o=>o.orgname==selectedOrgName)) 
{
    PD.cats.InsertOnSubmit(new Category { orgid = o.orgId, catname = newCatName });
}

      

        
        
        
      

    

The catch here is no if statements and it handles one or more cases. There is a way to do this on one line and remove the explicit for each and use List.ForEach ( see Comparisons ):

PD.orgs.Where(o=>o.orgname==selectedOrgName).ToList()
.ForEach(o=>PD.cats.InsertOnSubmit(new Category { orgid = o.orgId, catname = newCatName }));

      

        
        
        
      

    

Option 2 - use an exception

This will let you know what your intentions are for the code and let Visual Studio know that you've taken care of it. The idea is to keep the code very close to how it is now:

int selectedOrgId; 
foreach (Organization o in PD.orgs) 
{
    if (o.orgname == selectedOrgName) 
       selectedOrgId = o.orgid;
}

      

        
        
        
      

    

However, at this point, I would suggest using an exception like:

if(selectedOrgId == 0) throw new InvalidDataException("Selected Org Id cannot be 0");
PD.cats.InsertOnSubmit(new Category { orgid = selectedOrgId, catname = newCatName });

      

        
        
        
      

    

This is not the only problem. You know you will find 1 or more matches, the compiler doesn't know.

But the problem "or more" is also a problem. The code just isn't clear what you want, what's the reason. You have an implied "last win" strategy.

When you use a solution that meets the requirement more closely, the compiler problem goes away without any hacks.

Without Linq:

// int selectedOrgId; 

foreach (Organization o in PD.orgs)
    if (o.orgname == selectedOrgName)
    {
       PD.cats.InsertOnSubmit(new Category {
         orgid = o.orgid,
         catname = newCatName
      }); 
      return;   // or break;
    }
// shouldn't get here
throw new ...

      

        
        
        
      

    

And with Linq

Organization org =  PD.orgs.Single(o => o.orgname == selectedOrgName);
PD.cats.InsertOnSubmit(new Category {
          orgid = selectedOrgId,
          catname = newCatName
       }); 

      

        
        
        
      

    

The method is Single(Predicate)

fully consistent with your problem. It will throw when the result set has! = 1 element.

Use linq to select an organization with selectedOrgName

and get orgid

:

PD.cats.InsertOnSubmit(new Category { 
    orgid = PD.orgs.First(o => o.orgname == selectedOrgName).orgid, 
    catname = newCatName
});

      

        
        
        
      

    

Assumes it selectedOrgName

will always be in PD.orgs

, and I am making this assumption based on the variable name; however, if this is not always the case, you can do the following:

var selectedOrg = PD.orgs.FirstOrDefault(o => o.orgname == selectedOrgName);

if (selectedOrg != null)
{
    PD.cats.InsertOnSubmit(new Category { 
        orgid = selectedOrg.orgid, 
        catname = newCatName
    });
}