python manage.py inspectdb makes all fields with a default value blank=True, null=True

[Kimball Leavitt]

Wasn't sure on the category or difficulty of fix, so logged it as an "easy pickings bug".

I'm using:

Ubuntu 16.04
Python 3.7.0
Django 2.0.4
Mariadb 10.2.16

Before I get into this, I realize that
-"Django is best suited for developing new applications"
-This probably isn't a huge deal or a high priority
...BUT I figured I'd submit this anyway while I was thinking about it. Maybe it'll save someone some extra work down the line.

Steps to reproduce:

1. Setup a legacy db in settings.py (see ​https://docs.djangoproject.com/en/2.0/howto/legacy-databases/)

-Prerequisite: you have a column in one of your tables that has a default value.
-Example: test_field int(11) DEFAULT 1

2. Run python manage.py inspectdb [--database DATABASE_NAME [ TABLE ] ] > models.py (or don't include "> models.py" and you can view the results from the command line)
3. Open models.py

-test_field will look something like this:

test_field = models.IntegerField(blank=True, null=True)

-What I would expect:

test_field = models.IntegerField(default=1)

What I've been able to dig up:

# ​https://www.google.com/url?q=https%3A%2F%2Fgithub.com%2Fdjango%2Fdjango%2Fblob%2Fmaster%2Fdjango%2Fcore%2Fmanagement%2Fcommands%2Finspectdb.py%23L144&sa=D&sntz=1&usg=AFQjCNGZLkFkaqIJ1Ap1dhXRB0jARXcCoA
# from inspectdb.py (line 144, comments included in the original file, )

142  # Add 'null' and 'blank', if the 'null_ok' flag was present in the
143  # table description.
144  if row[6]:  # If it's NULL...
145      extra_params['blank'] = True
146      extra_params['null'] = True

# ​https://github.com/django/django/blob/master/django/db/backends/mysql/introspection.py#L95+info.column_default
# from introspection.py in get_field_description (line 95, comment is mine)

86  fields = []
87  for line in cursor.description:
88         info = field_info[line[0]]
89         fields.append(FieldInfo(
90               *line[:3],
91              to_int(info.max_len) or line[3],
92              to_int(info.num_prec) or line[4],
93              to_int(info.num_scale) or line[5],
94              line[6],
95              info.column_default, # THIS LINE IS JUST WHATEVER THE COLUMN DEFAULT IS
96              info.extra,
97              info.is_unsigned,
98          ))
99  return fields

I'm sure there are a lot of things I don't understand about this, but I don't think that having a default value should automatically add blank=True, null=True.
Is having a default value really a "'null_ok' flag"?

I think it should only put blank=True, null=True if the default is set to NULL in the column. Otherwise, it should set the default to whatever the default value is (ex: default=1)

Caveat: I've only tested this with int fields.

[Tim Graham]

I think you made a mistake in your analysis. In the FieldInfo initialization, line[6] (not info.column_default) corresponds to row[6] in inspectdb. In your example, test_field int(11) DEFAULT 1 seems to be nullable (according to the MySQL documentation, "If neither NULL nor NOT NULL is specified, the column is treated as though NULL had been specified." -- I guess it's the same for MariaDB.

As ​the documentation says, "database defaults aren’t translated to model field defaults or detected in any fashion by inspectdb."