选择Lambda Expression并检查Null Value

Question

public List<CompanyRatingInfo> GetTopCompanies()
        {
            return objectContext.Companies.OrderBy(c => c.Reviews.Sum(r => r.Rating))
                .Select(co => new CompanyRatingInfo()
                {
                    CompanyID = co.CompanyID,
                    CompanyName = co.Name,
                    CreateDate = co.CreateDate,
                    Logo = co.Logo,
                    Rating = co.Rating ?? 0,
                    ReviewsCount = (co.Reviews != null ? co.Reviews.Count : 0),
                    WebSite = co.Website
                }).ToList();
        }

ERROR: Cannot compare elements of type 'System.Data.Objects.DataClasses.EntityCollection`1'. Only primitive types (such as Int32, String, and Guid) and entity types are supported.

How can i obtain ReviewsCount with checking co.Reviews != null ?

`Company` has many `Reviews` which has `Rating`

Answer 1

It should be co.Reviews.Count() . Count is a method.