LinQ获得明显的字段与平均数错误

Question

我有一个“类型预期”的错误，我不知道为什么。

我的查询只是将3个表连在一起，同时试图获得不同的包和平均评级数。

的结果应该是这样的

| 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))); 

类型预计发生在。选择（C =>新（.....

我可以知道我有错误的查询？

因为

1）I内加入我的所有3代表一起

2）假设我所有的表连接，我试图将它们组由PACKAGENAME到不同的名称的一个名称

3）我试图选择相同包装的评分的平均总和。

任何想法，如果有更好的解决方案呢？

database class diagram

Solution error

Answer 1

你需要回到结果存储到一个新的变量，以匹配新类型：

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) 
       };