inspectdb sets max_length to -1 if no field length specified in the DB schema

[rvernica]

Postgres schema:

# \d instance
                   Table "public.instance"
       Column       |            Type             | Modifiers 
--------------------+-----------------------------+-----------
 instance_id        | bigint                      | not null
 membership_id      | bigint                      | default 0
 host               | character varying           | 
 port               | integer                     | 
 online_since       | timestamp without time zone | 
 base_path          | character varying           | 
 server_id          | integer                     | 
 server_instance_id | integer                     | 
Indexes:
    "instance_pkey" PRIMARY KEY, btree (instance_id)
    "instance_host_port_key" UNIQUE CONSTRAINT, btree (host, port)
    "instance_host_server_id_server_instance_id_key" UNIQUE CONSTRAINT, btree (host, server_id, server_instance_id)
    "instance_server_id_server_instance_id_key" UNIQUE CONSTRAINT, btree (server_id, server_instance_id)
Check constraints:
    "instance_base_path_non_unique" CHECK (check_base_path(base_path) = 0)

Notice the type for host and base_path attributes.

inspectdb output:

# python3 manage.py inspectdb instance
# This is an auto-generated Django model module.
# You'll have to do the following manually to clean this up:
#   * Rearrange models' order
#   * Make sure each model has one field with primary_key=True
#   * Make sure each ForeignKey has `on_delete` set to the desired behavior.
#   * Remove `managed = False` lines if you wish to allow Django to create, modify, and delete the table
# Feel free to rename the models, but don't rename db_table values or field names.
from __future__ import unicode_literals

from django.db import models


class Instance(models.Model):
    instance_id = models.BigIntegerField(primary_key=True)
    membership_id = models.BigIntegerField(blank=True, null=True)
    host = models.CharField(max_length=-1, blank=True, null=True)
    port = models.IntegerField(blank=True, null=True)
    online_since = models.DateTimeField(blank=True, null=True)
    base_path = models.CharField(max_length=-1, blank=True, null=True)
    server_id = models.IntegerField(blank=True, null=True)
    server_instance_id = models.IntegerField(blank=True, null=True)

    class Meta:
        managed = False
        db_table = 'instance'
        unique_together = (('host', 'port'), ('server_id', 'server_instance_id'), ('host', 'server_id', 'server_instance_id'),)

Notice the max_length=-1 for host and base_path attributes.

The django.contrib.postgres app is listed in INSTALLED_APPS

PostgreSQL 9.6.5
Python 3.6.1
Django 1.11.5

[Tim Graham]

Until Django supports CharField with max_length=None (#14094), I'm not sure what the expected behavior would be. Can we close this as a duplicate of that ticket or do you think we should make some other change in the meantime?

[Mariusz Felisiak]

Agreed. It should be closed as a duplicate. IMO the only possible solution is to treat them as a TextField's (at least on PostgreSQL) but this is not exactly the same.

[Shai Berger]

If we're ready to accept the current situation -- where inspectdb produces output which cannot be used without changes, until #14094 is fixed -- then I think we can define the expected behavior as producing a CharField with max_length=None or no max_length at all. Leaving this open may have some value then: I suspect that, when taken on its own, this is an "easy pickings" ticket, and there's little motivation for experienced contributors to fix it.