[Django]-Django model – set default charfield in lowercase

While overwriting save() method is a valid solution. I found it useful to deal with this on a Field level as opposed to the Model level by overwriting get_prep_value() method.

This way if you ever want to reuse this field in a different model, you can adopt the same consistent strategy. Also the logic is separated from the save method, which you may also want to overwrite for different purposes.

For this case you would do this:

class NameField(models.CharField):
    # Ensure valid values will always be using just lowercase
    def get_prep_value(self, value):
        value = super().get_prep_value(value)
        return value if value is None else value.lower()

class User(models.Model):
    username = models.CharField(max_length=100, unique=True)
    password = models.CharField(max_length=64)
    name = NameField(max_length=200)
    phone = models.CharField(max_length=20)
    email = models.CharField(max_length=200)

signals also works

from django.db.models.signals import pre_save

@receiver(pre_save, sender=YourModel)
def to_lower(sender, instance=None, **kwargs):
    instance.text = instance.text.lower() if  \
        isinstance(instance.text, str) else ''

In my case I had a recipient_name field that I needed to make all lower case when it is stored on DB

class LowerField(models.CharField):

    def get_prep_value(self, value):
        return str(value).lower()

class Recipients(models.Model):
    
    user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='recipients', on_delete=models.CASCADE, )
    recipient_account_number = models.IntegerField()
    recipient_name = LowerField(max_length=30)
    recipient_bank_name = models.CharField(max_length=30)
    date = models.DateTimeField(auto_now=True, verbose_name='Transaction Date')
    
    class Meta:
        ordering = ['-date']

    def __str__(self):
        return self.recipient_name

    def get_absolute_url(self):
        return reverse('recipient-detail', kwargs={'pk': self.pk})

Similarly, you can apply to another table called Transactions in your app, like this

class Transactions(models.Model):

    transaction_type = (
        ('transfer', 'Transfer'),
        )

    user = models.ForeignKey(settings.AUTH_USER_MODEL, related_name='transactions', on_delete=models.CASCADE, )
    bank_name = LowerField(max_length=50)

def save(self, force_insert=False, force_update=False):
        self.YourFildName = self.YourFildName.upper()
        super(YourFomrName, self).save(force_insert, force_update)