想要一周的efcore sql语法，流畅的api方法

Question

Department {int Id，string Title，Staffs}

Staff {int Id，string Name，int DeptId}

var DeptStaff = 
from dept in _context.Departments 
select new 
{ 
   Department= dept, 
   StaffCount = 
      (from staff in _context.Staffs 
       where staff.DeptId == dept.Id 
       select staff).Count()
}

Staffs是Department类中的导航属性 在内部查询中给出错误