using regex validators in django models

from django.db import models
from django.core.validators import RegexValidator

class YourModel(models.Model):
    your_field = models.CharField(
        max_length=100,
        validators=[
            RegexValidator(
                regex=r'^[A-Za-z0-9_]+$',
                message='Only letters, numbers, and underscores are allowed.',
                code='invalid_your_field'
            ),
        ]
    )