static async Task ShowRegistrations_Good(IDac dac)
{
// Registrations
var regs = await dac.GetRegistrations(it => true);
// Students
var relatedStudentIdQry = regs.Select(it => it.StudentId).Distinct();
var students = await dac.GetStudents(it => relatedStudentIdQry.Contains(it.Id));
// Subjects
var relatedSubjectIdQry = regs.Select(it => it.SubjectId).Distinct();
var subjects = await dac.GetSubjects(it => relatedSubjectIdQry.Contains(it.Id));
// Teachers
var relatedTeacherIdQry = subjects.Select(it => it.TeacherId).Distinct();
var teachers = await dac.GetTeachers(it => relatedTeacherIdQry.Contains(it.Id));
foreach (var reg in regs)
{
var student = students.FirstOrDefault(it => it.Id == reg.StudentId);
var subject = subjects.FirstOrDefault(it => it.Id == reg.SubjectId);
var teacher = teachers.FirstOrDefault(it => it.Id == subject.TeacherId);
Console.WriteLine($"{reg.Id:00}|{subject.Name}, {student.Name}, {teacher.Name}, {reg.Semester}, {reg.Grade}");
}
}