LinQ獲得明顯的字段與平均數錯誤

Question

我有一個「類型預期」的錯誤，我不知道爲什麼。

我的查詢只是將3個表連在一起，同時試圖獲得不同的包和平均評級數。

的結果應該是這樣的

| PackageName | Average Rating | 
| SG  |  4  | 
| USA  |  4  |  

---

 IQueryable<Recommendation> recommendationQuery = db.Recommendations; 
     IQueryable<Booking> bookingQuery = db.Bookings; 
     IQueryable<Package> packageQuery = db.Packages; 

     recommendationQuery = (from recommendationItem in recommendationQuery 
           join bookingItem in bookingQuery 
           on recommendationItem.BookingId equals bookingItem.BookingId 
           join packageItem in packageQuery 
           on recommendationItem.Booking.PackageId equals packageItem.PackageId 
           select recommendationItem).GroupBy(c => c.Booking.Package.PackageTitle) 
           .Select(c => new (c.Key, c.Average(d=>d.Rating))); 

類型預計發生在。選擇（C =>新（.....

我可以知道我有錯誤的查詢？

因爲

1）I內加入我的所有3代表一起

2）假設我所有的表連接，我試圖將它們組由PACKAGENAME到不同的名稱的一個名稱

3）我試圖選擇相同包裝的評分的平均總和。

任何想法，如果有更好的解決方案呢？

database class diagram

Solution error

Answer 1

你需要回到結果存儲到一個新的變量，以匹配新類型：

var results = from recommendationItem in recommendationQuery 
       join bookingItem in bookingQuery 
       on recommendationItem.BookingId equals bookingItem.BookingId 
       join packageItem in packageQuery 
       on recommendationItem.Booking.PackageId equals packageItem.PackageId 
       group recommendationItem 
       by recommendationItem.Booking.Package.PackageTitle 
       into grp 
       select new 
       { 
        PackageName = grp.Key, 
        AverageRating = grp.Average(d => d.Rating) 
       };