如何從此linq查詢中過濾出null？

Question

我有遍歷列表列表的代碼。

    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();
    }

問題：如何修改代碼以處理FromDate返回null？

注意：我永遠不會想出如何編寫此查詢，但是重新嵌套是通過嵌套的foreach循環為我完成的，現在我很想知道是否可以使它工作...

更新：這是最終的linq查詢，以及原始的非linq方法被注釋掉了。

        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

怎么樣

int date select (FromDate(date) ?? new AffiliateList())

要么

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)

Answer 2

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

原諒我沒有使用查詢語法，我只是發現方法鏈更具表現力。

另請注意，此代碼是在沒有任何IDE的情況下編碼的，因此可能會出現錯誤。