Table Student
id int primary key
name nchar(10)
class_id int FOREIGN KEY to class'id

Table Class
id int primary Key
name nchar(10)

基于.net Core 3，实体框架核心，SQL 2012的测试 发现异常“ NavigationExpandingExpressionVisitor”。

var query = _context.TestClass.GroupJoin(_context.TestStudent,cla = > cla.Id,stu = > stu.ClassId,(cla,stuCollection) = > new {
        classname = cla.Name,studentsnames = stuCollection.Select(s = > s.Name)
    }
);
foreach(var arr in query) {
    Console.WriteLine("Class {0} Has {1} Students",arr.classname,arr.studentsnames.Count());
}