连接两个表时出现 System.InvalidOperationException

Question

In project i have two tables

• Restaurant (RestaurantId, Name, Adress)
• RestaurantReview (ReviewId, RestaurantId, Mark)

I want to display one restaurant and calculate its average Mark

var lj = (from x in _context.Restaurant
         join y in _context.RestaurantReview on x.RestaurantId equals y.RestaurantId into z
         select new
         {
              Name= x.Name,
              Total = z.Average(x => Convert.ToInt32(x.Mark))
         }).ToList();

while run this code i got error

System.InvalidOperationException: „Processing of the LINQ expression 'GroupJoin<Restaurant, RestaurantReview , int, <>f__AnonymousType4<string, double>>(
    outer: DbSet<Restaurant>, 
    inner: DbSet<RestaurantReview >, 
    outerKeySelector: (x) => x.RestaurantId, 
    innerKeySelector: (y) => y.RestaurantId, 
    resultSelector: (x, z) => new { 
        Name = x.Name , 
        Total = Average<RestaurantReview >(
            source: z, 
            selector: (x) => ToInt32(x.mark))
     })' by 'NavigationExpandingExpressionVisitor' failed. This may indicate either a bug or a limitation in EF Core. 

I try use other query, but every time I get the same error

Answer 1

group by missing in your code. Add group by in linq expression