Confused about how to make Django model field optional

Question

I have an 'address' field in my Django model that I want to be optional:

class Home(models.Model):
    address = models.CharField(max_length=256, blank=True, default=None)
    city = models.CharField(max_length=25)

I want this to be an optional field in my database but I didn't set "null=True" because the documentation says

"Avoid using null on string-based fields such as CharField and TextField because empty string values will always be stored as empty strings, not as NULL. If a string-based field has null=True, that means it has two possible values for “no data”: NULL, and the empty string. In most cases, it’s redundant to have two possible values for “no data;” the Django convention is to use the empty string, not NULL."

However, when I create a Home object with this command:

Home.objects.create(city='Chicago')

I get an error:

IntegrityError: null value in column 'address' violates not-null constraint.

Shouldn't I add "null=True" to the address field despite what the docs say in order to make it optional? If not, how should it be declared so that I can create new Home objects without raising this error?

May you want to set 'default' value? https://docs.djangoproject.com/en/1.10/ref/models/fields/#default — Alex Kroll, Dec 06 '16 at 19:32
Also see answers for this question. http://stackoverflow.com/questions/755857/default-value-for-field-in-django-model — Alex Kroll, Dec 06 '16 at 19:34
Just leave out the `default` and the default value will be the empty string. — Kevin Christopher Henry, Dec 06 '16 at 19:41
'None' is a NULL constraint obviously. Just assign empty string to default value. I'm not agree with Kevin. — Alex Kroll, Dec 06 '16 at 19:48

score 5 · Answer 1 · answered Dec 06 '16 at 19:47

5

You should get rid of default=None, otherwise, you can just use default=''

answered Dec 06 '16 at 19:47

Hybrid

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I think that this is the best way to do it, because it is consistent with how Django represents empty CharFields. – souldeux Dec 06 '16 at 20:06
When I make this change and examine my PostgreSQL database table schema, it still says that the address field is "not null". – Jim Dec 06 '16 at 22:38
Did you run 'manage.py makemigrations' and 'manage.py migrate'? – Hybrid Dec 06 '16 at 22:39
Ok great, but is this new issue an error, or it just says the field is not null? – Hybrid Dec 06 '16 at 22:51
When doing \d, the database schema just says that the address field is "not null" It's not a database error. – Jim Dec 06 '16 at 23:07
Sounds like it's working - `not null` would make sense, considering that `default=''` is an empty string (and therefor not null) – Hybrid Dec 06 '16 at 23:07

score 0 · Accepted Answer · answered Dec 06 '16 at 20:34

0

if you not always add address you need to add

null= True

because default is set to None but the DB isn't set to accept null's

answered Dec 06 '16 at 20:34

Tal.S

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I don't understand why the documentation says what it does without addressing this issue so I'm just going to set "null=True" as I usually do. – Jim Dec 07 '16 at 00:05

Confused about how to make Django model field optional

2 Answers2