Custom django validation function

Question

i have written validaiton function for an attribute is it correct and how should i write for same attribute with blank = True and add_1 is required field any conditions to add

add_1 = models.CharField(max_length=255)
add_2 = models.CharField(max_length=255, blank=True)

Note: All validators must return True or False

validators.py

def validate_add_1(value):
    if value is not None:
        try:
            if len(value) <= 255:
                return True
        except ValidationError:
            return False

Answer 1

According to Model Reference, when you add the "blank=True" attribute to any model field, that that field becomes optional. If you want a field to be required, do not specify blank attribute as the default is blank=False.

For validator, I'm not sure what you are trying to do, but you can try something like this:

def validate_add_1(value):
    val_len = False if len(value) > 255 else True
    # Return True if value is not blank/null and length of value <= 255
    return True if val_len and (value and value != '') else False

Edit

To simplify the above code for you to understand:

def validate_add_1(value):

    # If length of value > 255, return False, else check for blank = True

    if len(value) > 255:
        return False
    else:

        # If value is not blank, AND value is not an empty string.
        # This is for checking blank = True condition is satisfied.

        if value and value != '':
            return True
        else:
            return False