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

[Kimball Leavitt]

Note: I posted this on django-users and was told to come here.

I'm not sure if this is a bug, feature request, or something else.

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
• If you don't include > models.py you can see the output from the commandline
• 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.

[Kimball Leavitt]

I opened a ticket for it here --> https://code.djangoproject.com/ticket/29583

[Collin Anderson]

It's tricky to automatically convert the database default value to python, but I wonder if it would help to put the default value in a python comment at the end of the field? like:

models.IntegerField(blank=True, null=True)  # DB Default value: 1

That way it's more clear in models.py what's going on in the database, and you can more easily change the model yourself if you want.

--
You received this message because you are subscribed to the Google Groups "Django developers (Contributions to Django itself)" group.
To unsubscribe from this group and stop receiving emails from it, send an email to django-develop...@googlegroups.com.
To post to this group, send email to django-d...@googlegroups.com.
Visit this group at https://groups.google.com/group/django-developers.
To view this discussion on the web visit https://groups.google.com/d/msgid/django-developers/a6aedffd-a04b-4c38-8218-850aa3394364%40googlegroups.com.
For more options, visit https://groups.google.com/d/optout.