models and serializers

class TimetableSerializer(serializers.ModelSerializer):
    group = GroupSerializer()
    day = DaySerializer()
    name_of_class = ClassSerializer()
    cabinet = CabinetSerializer()

    class Meta:
        model = Timetable
        fields = ['id', 'number_of_class', 'group', 'day', 'name_of_class', 'cabinet']
    # Объект создается. Сделать проверку существование get() полей. Сделайть чтобы при занятии кабинета
    # в какой либо из дней нельзя было его на этот же день поставить
    def create(self, validated_data):
        group = Group.objects.get(number=validated_data['group']['number'])
        day = validated_data.pop('day')
        day = Day.objects.get_or_create(day=day['day'], day_of_week=day['day_of_week'])
        cabinet = Cabinet.objects.get(number=validated_data['cabinet']['number'])
        name_of_class = Class.objects.get(name=validated_data['name_of_class']['name'])
        number_of_class = validated_data['number_of_class']
        timetable = Timetable.objects.create(group=group, day=day[0], cabinet=cabinet, name_of_class=name_of_class, number_of_class=number_of_class)

        return timetable
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Модели

class Day(models.Model):
    '''Model with date and day of week'''
    day = models.DateField()
    day_of_week = models.CharField(max_length=10)

    class Meta:
        verbose_name = 'День'
        verbose_name_plural = 'Дни'

    def __str__(self):
        return f'{self.day_of_week}-{self.day}'


class Group(models.Model):
    '''Model with number of group'''
    number = models.CharField(max_length=6)
    slug = models.SlugField(max_length=10, default='empty')

    class Meta:
        verbose_name='Группа'
        verbose_name_plural='Группы'

    def __str__(self):
        return f'Группа {self.number}'

    def save(self, *args, **kwargs):
        self.slug = slugify(self.number)
        super(Group, self).save(*args, **kwargs)



class Cabinet(models.Model):
    '''Model with cabinets and their status'''
    number = models.CharField(max_length=5)
    is_free = models.BooleanField(default=True)

    class Meta:
        verbose_name='Кабинет'
        verbose_name_plural='Кабинеты'

    def __str__(self):
        return f'Кабинет {self.number}'


class Class(models.Model):
    '''Model with name of academic classes'''
    name = models.CharField(max_length=25)

    class Meta:
        verbose_name='Пара'
        verbose_name_plural='Пары'

    def __str__(self):
        return self.name


class Timetable(models.Model):
    '''Model integraated all other models'''
    day = models.ForeignKey(Day, related_name='timetables', on_delete=models.CASCADE)
    group = models.ForeignKey(Group, related_name='timetables', on_delete=models.CASCADE)
    cabinet = models.ForeignKey(Cabinet, related_name='timetables', on_delete=models.CASCADE)
    name_of_class = models.ForeignKey(Class, related_name='timetables', on_delete=models.CASCADE)
    number_of_class = models.PositiveSmallIntegerField()

    class Meta:
        verbose_name='Расписание'
        verbose_name_plural='Расписание'

    def __str__(self):
        return f'{self.day.day} - {self.group.number} - {self.name_of_class.name}'