如何編寫此復雜的LINQ to Entities查詢

Question

我正在寫一個應用程序，它將允許我們的用戶向他們的聯系人發送新聞通訊。 這是數據庫結構（僅重要字段）：

Contacts(tbl)       ContactEmails(tbl)       Newsletters(tbl)
  ContactID           ContactEmailID           NewsletterID
  ...                 ContactID (fk)           ...
                      EmailAddress             
                      Deleted
                      ...


NewsletterLists(tbl)       NewsletterToLists(tbl)
  NewsletterListID           NewsletterID (fk)
  ...                        NewsletterListID (fk)


NewsletterListToContacts(tbl)
  NewsletterListID (fk)
  ContactID (fk)
  Active
  Deleted
  UnsubscribedOn
  ...

現在，我有一個類結構如下：

public class NewsletterContactEmails
{
    public int ContactID { get; set; }
    public List<string> EmailList { get; set; }
}

我希望每個聯系人都有一個NewsletterContactEmails對象，以便我可以遍歷該對象並為每個聯系人發送一封電子郵件（而不是每個電子郵件地址）。

我有Newsletter對象開始使用。 所以用偽裝將是...

1. Get NewsletterLists this newsletter is to send to.
2. Get Active (double opted-in) and non-deleted/unsubscribed DISTINCT Contact List from said NewsletterLists.
3. Create NewsletterContactEmails object for each contact and add their non-deleted DISTINCT list of email addresses.

我想在一個查詢中執行此操作。 這是我目前擁有的東西，我想我已經接近了，但這甚至無法編譯：

List<NewsletterContactEmails> Recipients = objNewsletter.NewsletterToLists
                    .Select(ntl => ntl.NewsletterList.NewsletterListToContacts
                        .Where(nl => nl.Active == true && nl.Deleted == false && nl.UnsubscribedOn == null)
                        .Select(nl => new NewsletterContactEmails {
                            ContactID = nl.ContactID,
                            EmailList = nl.Contact.ContactEmails.Where(ce => ce.Deleted == false).Select(ce => ce.EmailAddress).Distinct().ToList()
                        }));

任何幫助是極大的贊賞！

Answer 1

List<NewsletterContactEmails> Recipients = objNewsletter.NewsletterToLists
    .SelectMany(ntl => ntl.NewsletterList.NewsletterListToContacts
        .Where(nl => nl.Active == true && nl.Deleted == false && nl.UnsubscribedOn == null)
        .Select(nl => new NewsletterContactEmails
        {
            ContactID = nl.ContactID,
            EmailList =
                nl.Contact.ContactEmails.Where(ce => ce.Deleted == false)
                    .Select(ce => ce.EmailAddress)
                    .Distinct()
                    .ToList()
        }));

嘗試將第一個選擇作為SelectMany而不是Select