Custom Class not working well

import '../backend/backend.dart';
import 'package:cloud_firestore/cloud_firestore.dart';

class DaySessionsByClass {
  ClassesRecord? classRecord;
  List<SessionsRecord> sessions;
  List<BookingsRecord> bookings;

  DaySessionsByClass({
    this.classRecord,
    this.sessions = const [],
    this.bookings = const [],
  });

  Future<List<DaySessionsByClass>> getRescheduledBookingsForToday(
      String providerId) async {
    final now = DateTime.now();
    final todayStart = DateTime(now.year, now.month, now.day);
    final tomorrowStart = todayStart.add(const Duration(days: 1));

    // Query all bookings for this provider, rescheduled, with reschedule_time today
    final bookingsQuery = await FirebaseFirestore.instance
        .collection('bookings')
        .where('provider',
            isEqualTo: FirebaseFirestore.instance.doc(providerId))
        .where('rescheduled', isEqualTo: true)
        .where('reschedule_time',
            isGreaterThanOrEqualTo: Timestamp.fromDate(todayStart))
        .where('reschedule_time', isLessThan: Timestamp.fromDate(tomorrowStart))
        .get();

    // Group bookings by class_reference
    final Map<String, List<BookingsRecord>> bookingsByClass = {};
    for (var doc in bookingsQuery.docs) {
      final booking = BookingsRecord.fromSnapshot(doc);
      final classRef = booking.classReference?.id; // Use .id to get the classId
      if (classRef != null) {
        bookingsByClass.putIfAbsent(classRef, () => []).add(booking);
      }
    }

    // Fetch ClassesRecord for each classId
    List<DaySessionsByClass> results = [];
    for (var entry in bookingsByClass.entries) {
      final classId = entry.key;
      final classDoc = await FirebaseFirestore.instance
          .collection('classes')
          .doc(classId)
          .get();
      final classRecord = ClassesRecord.fromSnapshot(classDoc);

      results.add(DaySessionsByClass(
        classRecord: classRecord,
        bookings: entry.value,
      ));
    }

    return results;
  }
}