Documentation not clear about the effects of max_length for IntegerField

[msn@…]

With a model like this:

from django.db import models


class Dummy(models.Model):
    id = models.IntegerField(max_length=10, primary_key=True)

makemigrations creates:

# -*- coding: utf-8 -*-
from __future__ import unicode_literals

from django.db import models, migrations


class Migration(migrations.Migration):

    dependencies = [
    ]

    operations = [
        migrations.CreateModel(
            name='Dummy',
            fields=[
                ('id', models.IntegerField(max_length=10, serialize=False, primary_key=True)),
            ],
            options={
            },
            bases=(models.Model,),
        ),
    ]

After running the migration I run the following MySQL:

mysql> describe dummy_dummy;
+-------+---------+------+-----+---------+-------+
| Field | Type    | Null | Key | Default | Extra |
+-------+---------+------+-----+---------+-------+
| id    | int(11) | NO   | PRI | NULL    |       |
+-------+---------+------+-----+---------+-------+
1 row in set (0,01 sec)

I expected type to be int(10) but instead I get int(11) which is the default for IntegerField. Not sure if this is expected behavior or not, but I'd expect the max_length parameter to alter the type. If that's not the case I'd be glad to hear if there's another way to alter it.

[Shai Berger]

Hello,

Thanks for taking care to submit this detailed report. Actually, max_length is not a documented option for IntegerField, and AFAIK it only modifies the widget that is generated for the field in forms by default.

If you want to specify exactly the parameters of a numeric database column, use DecimalField.

I am recasting this as a documentation bug.

[sabinemaennel]

I am working on this on the Django Con

[sabinemaennel]

Hello ,
I just tested this. This is my result:

Assigning the option max_length to an IntegerField in your model does not have any effect, neither on the database where the field is just generated as an models.IntegerField() nor on the Admin Form, where the field is always generated as "type=text"and class="vIntegerField". So it does not really make sense to have that option here.

I talked about this with chai about this and the opinion was that the option should not be forbidden in order to keep Django upward compatible, but that it also does not make sense for the IntegerField.

[Tim Graham]

I don't think there's value in documenting parameters that don't appear in the documentation have no effect.