Is some problem in field options 'null'?

[Jinwen]

I read the document about field options 'null'.

It is said that.

If True, Django will store empty values as NULL in the database. Default is False.

Avoid using null on string-based fields such as CharField and TextField. If a string-based field has null=True, that means it has two possible values for “no data”: NULL, and the empty string.

Then I try make a field have "null=True", just save it to database.

like that.

>>> from backend.models import Scrapyd as S

>>> s = S()

>>> s.comment

>>> type(s.comment)

<class 'NoneType'>

>>> s.save()

>>> b  = S.objects.all().last()

>>> b

<Scrapyd: Scrapyd object>

>>> b.comment

>>> type(b.comment)

<class 'NoneType'>

What my question is why the value not like the document said is empty string ''?

I am confused.

[Melvyn Sopacua]

The document says to avoid null=True for character fields,

because they both "mean the same thing": there is nothing

in there.

They are however different and this is why Django returns

None:

- Empty character fields are considered a value

- NULL character fields are not

This is important in unique constraints:

Two rows with empty string are forbidden

Two (or more) rows set to NULL are allowed.

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Melvyn Sopacua