SELECT
GL.Id as GradeLevels, CRS.Name as CourseName, GL.Title as GradlevelName, avg(ASTSTU.ObtainedMarks) FROM
GradeLevels AS GL
    inner JOIN
Courses AS CRS ON CRS.GradeLevelsID = GL.Id
    inner JOIN
Units AS UNT ON UNT.CourseID = CRS.ID
    inner JOIN
Lessons AS LSN ON LSN.UnitsId = UNT.Id
    inner JOIN
Assignments AST ON AST.LessonId = LSN.id
    inner JOIN
AssignmentStudents ASTSTU ON ASTSTU.AssignmentId = AST.id
 WHERE
CRS.SchoolSystemsID = "08d6a1f2-26df-4ad5-25d3-2a26960aa3fd"  //School System id.
                GROUP BY GL.Id;

public async Task<ICollection<GradeLevels>> GetSchoolSystemGradLevelsAverage(Guid schoolSystemId)
    {
        List<GradeLevels> dashboadOverAllAverage = new List<GradeLevels>();

        var dashboadOverAllAverage1 = await _GpsContext.GradeLevels
            .Include(d=>d.Departments)
            .ThenInclude(c=>c.Courses.Where(s=>s.SchoolSystemsID ==schoolSystemId))
            .ThenInclude(u=>u.Units)
            .ThenInclude(l=>l.Lessons)
            .ThenInclude(a=>a.Assignment)
            .ThenInclude(a=>a.assignmentStudents)
            .GroupBy(g=>g.ID)
            .ToListAsync();
        return dashboadOverAllAverage;
    }

[HttpGet()]
    public async Task<IActionResult> GetCEOGradeLevelAverage(string schoolSystemId)
    {
        var overallgradeAverages = await _ceoDashboadRepository.GetSchoolSystemGradLevelsAverage(Guid.Parse(schoolSystemId));
        List<GetGradeLevelAverageVm> getOverallAverageVms = new List<GetGradeLevelAverageVm>();

        foreach (GradeLevels overallgradeAverage in overallgradeAverages)
        {
            getOverallAverageVms.Add(new GetGradeLevelAverageVm
            {
                Marks = overallgradeAverage.Id.ToString(), //Want to show lable of AvrageMark
                Name = overallgradeAverage.Name //Want to show Gradelevel name
            });
        }
        return Ok(getOverallAverageVms);
    }