Question

I have code that iterates over a list of lists.

    public static AffiliateList FromDate(string date)
    {
        Console.WriteLine("calling affiliates by date for " + date);
        AffiliateList al;
        try
        {
            al = new AffiliateList(DirectTrackXmlUtility.AffilaitesByDate(date));
        }
        catch (Exception)
        {
            return null;
        }
        return al;
    }

    public override IEnumerator<AffiliateItem> GetEnumerator()
    {
        return (from ru in Inner.resourceURL
                select ru.location
                into date select FromDate(date)
                into listForDate from ru2 in listForDate.Inner.resourceURL
                select AffiliateItem.From(ru2)).
            GetEnumerator();
    }

Question: How do I modify the code to handle FromDate returning null?

Note: I would never have figured out how to write this query, but re-sharper did it for me from my nested foreach loops, and now I’m interested to see if I can make it work…

Update: Here’s the final linq query, along with the original non-linq way commented out.

        return (from ru in Inner.resourceURL
                select ru.location
                into date select FromDate(date)
                into listForDate where listForDate != null from ru2 in listForDate.Inner.resourceURL
                select AffiliateItem.From(ru2)).GetEnumerator();
        //foreach (resourceListResourceURL ru in Inner.resourceURL)
        //{
        //    string date = ru.location;
        //    AffiliateList listForDate = FromDate(date);
        //    if (listForDate != null)
        //    {
        //        foreach (var ru2 in listForDate.Inner.resourceURL)
        //        {
        //            yield return AffiliateItem.From(ru2);
        //        }
        //    }
        //}

Answer 1

return Inner.resourceURL.Select(ru => FromDate(ru.location))
                        .Where(d => d != null)
                        .SelectMany(ru => 
                                    ru.Inner.resourceURL
                                      .Select(ru2 => AffiliateItem.From(ru2)))

Forgive me for not using the query syntax, I just find the method chain much more expressive.

Also note that this was coded without any IDE so there is a possibility of error.