models.py

# Create your models here.
from django.db import models
from django.core.validators import RegexValidator

class NumValidator(RegexValidator):
    regex = r'^[0-9]+\Z'
    message = "ゼッケンNoは数字のみで入力してください。"
    
    
    def __call__(self, value):
        return super().__call__(value)
    
class Foo(models.Model):
    val = NumValidator()
    num = models.CharField(verbose_name="番号", max_length=10, null=False, validators=[val])