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

[Kimball Leavitt]

I'm not sure if this is a bug, feature request, or something else, so I thought I'd start here.

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

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:

• 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
  
• Run python manage.py inspectdb [--database DATABASE_NAME  [ TABLE ] ] > models.py
• 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:

# 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

# 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.

Am I missing something?

[Jason]

Nice edge case you found.  I would suggest raising this to the django-developers to get core framework dev attention or make a bug report on the tracker.

[Kimball Leavitt]

Will do. Thanks.

[Tim Graham]

For future reference, creating a bug report is sufficient. No need to post to django-developers.

I'll post my analysis from the ticket below.

https://code.djangoproject.com/ticket/29583#comment:1

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."

[Kimball Leavitt]

Good to know, I’ll keep that in mind.

 

Yes, I was mistaken. And I guess I missed that line in the docs. Thanks!

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