Cannot implicitly convert type IEnumerable to System.Data.Linq.EntitySet. An explicit conversion exists (are you missing a cast?)

Cannot implicitly convert type IEnumerable<A> to System.Data.Linq.EntitySet. An explicit conversion exists (are you missing a cast?)

這是我開發時發生的問題。
大概是這樣的。

var q = from storeEl in buyerEl.Elements("store")
                      select new Store
              {
                StoreId = storeEl.Element("id").Value,
                TaxNo = buyerEl.Value,
                StoreName = storeEl.Element("cname").Value,
                Emails = from sub in storeEl.Elements("mails")
                                   select new StoreEmail
                                   {
                                     StoreId = storeEl.Attribute("id").Value,
                                     Email = sub.Attribute("email").Value
                                   },
              };

問題出現在 from sub in 那一段。Emails 是一個 EntitySet<Email>，而非 IEnumerable<Email>，於是發生了錯誤。

goole 了一下，找到了一個看來不是很好的方法。

  public static class LinqExtension
  {
    public static EntitySet ToEntitySet(this IEnumerable source) where T : class
    {
      var es = new EntitySet();
      es.AddRange(source);
      return es;
    }
  }

然後，將程式改為

var q = from storeEl in buyerEl.Elements("store")
                      select new Store
        {
                StoreId = storeEl.Element("id").Value,
                TaxNo = buyerEl.Value,
                StoreName = storeEl.Element("cname").Value,
                Emails = (from sub in storeEl.Elements("mails")
                                   select new StoreEmail
                                   {
                                     StoreId = storeEl.Attribute("id").Value,
                                     Email = sub.Attribute("email").Value
                                   }).ToEntitySet(),
        };