尽管我在开始时间之前提供了预约，但仍在登记预约。

• • 型号. py**

class Appointment(models.Model):
    status = models.CharField(
        choices=APPOINMENT_STATUSES,
        max_length=20,
        default=SCHEDULED,
        help_text="",
    )
    full_name = models.CharField(max_length=100)
    gender = models.CharField(choices=GENDER_TYPE, max_length=10, default=MALE)
    email =  models.EmailField()
    phone_no = models.CharField(max_length=10, validators=[validate_phone_no])
    start = models.DateTimeField(max_length=50, help_text="Appointment start Date & Time")
    end = models.DateTimeField(max_length=50, help_text="Appointment End Date & Time")
    doctor = models.ForeignKey(Doctor, on_delete=models.PROTECT, blank=True, null=True) 
    message = models.TextField()

    def __str__(self):
        return self.full_name

• • 序列化程序. py**

class AppointmentCreateSerializer(serializers.ModelSerializer):
    class Meta: 
        model = Appointment
        fields = '__all__'
 

    def create(self, validated_data):
        return super().create(validated_data)

    def validate(self, attrs):
        # check appointment start and end time

        if attrs["start"] < timezone.now():
            raise serializers.ValidationError("Appointment date cannot be in the past")

        if attrs["start"] >= attrs["end"]:
            raise serializers.ValidationError(
                f"Appointment end date/time should be after than start/date time."
            )
        return super().validate(attrs)

• • 说明：**

这是我的约会模型和序列化器。为什么我的验证不起作用。
我想，用户将无法创建约会，如果 * 开始 * 日期和时间是在当前日期和时间之前。---------------〉但约会正在注册，如果用户输入今天的日期，但之前的时间。

• 这有什么错？什么可以更好地解决这个问题？*