GeoDjango migrate giving the following error - ValueError: Cannot use object with type int for a spatial lookup parameter

Question

I'm trying to create a model with Geospatial field. When I try to migrate I receive the following error:

  Apply all migrations: admin, auth, contenttypes, map, sessions
Running migrations:
  Applying map.0008_territorio_geometry...Traceback (most recent call last):
  File "manage.py", line 21, in <module>
    main()
  File "manage.py", line 17, in main
    execute_from_command_line(sys.argv)
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\core\management\__init__.py", line 401, in execute_from_command_line
    utility.execute()
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\core\management\__init__.py", line 395, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\core\management\base.py", line 328, in run_from_argv
    self.execute(*args, **cmd_options)
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\core\management\base.py", line 369, in execute
    output = self.handle(*args, **options)
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\core\management\base.py", line 83, in wrapped
    res = handle_func(*args, **kwargs)
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\core\management\commands\migrate.py", line 231, in handle
    post_migrate_state = executor.migrate(
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\db\migrations\executor.py", line 117, in migrate
    state = self._migrate_all_forwards(state, plan, full_plan, fake=fake, fake_initial=fake_initial)
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\db\migrations\executor.py", line 147, in _migrate_all_forwards
    state = self.apply_migration(state, migration, fake=fake, fake_initial=fake_initial)
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\db\migrations\executor.py", line 245, in apply_migration
    state = migration.apply(state, schema_editor)
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\db\migrations\migration.py", line 124, in apply
    operation.database_forwards(self.app_label, schema_editor, old_state, project_state)
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\db\migrations\operations\fields.py", line 110, in database_forwards
    schema_editor.add_field(
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\db\backends\base\schema.py", line 450, in add_field
    definition, params = self.column_sql(model, field, include_default=True)
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\db\backends\base\schema.py", line 223, in column_sql
    default_value = self.effective_default(field)
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\db\backends\base\schema.py", line 303, in effective_default
    return field.get_db_prep_save(self._effective_default(field), self.connection)
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\db\models\fields\__init__.py", line 821, in get_db_prep_save
    return self.get_db_prep_value(value, connection=connection, prepared=False)
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\contrib\gis\db\models\fields.py", line 147, in get_db_prep_value
    super().get_db_prep_value(value, connection, *args, **kwargs),
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\db\models\fields\__init__.py", line 816, in get_db_prep_value
    value = self.get_prep_value(value)
  File "C:\Users\Marco\Envs\um\lib\site-packages\django\contrib\gis\db\models\fields.py", line 190, in get_prep_value
    raise ValueError('Cannot use object with type %s for a spatial lookup parameter.' % type(obj).__name__)
ValueError: Cannot use object with type int for a spatial lookup parameter. 

I also tried to remove attributes from my model but nothing changes. The following is my models.py

from django.contrib.gis.db import models

# Create your models here.
class Piano(models.Model):
    """Modello che rappresenta un piano"""
    titolo = models.CharField(max_length=100, help_text='Nome del piano')
    acronimo = models.CharField(max_length=100, help_text='Acronimo del piano')
    #fk_territorio = models.ForeignKey('Territorio', verbose_name='Territorio', on_delete=models.SET_NULL, null=True)

    def __str__(self):
        """String for representing the Model object."""
        return self.titolo

    class Meta:
        verbose_name_plural = "Piani"

class Territorio(models.Model):
    """Modello che rappresenta la tipologia di una norma"""
    nome = models.CharField(max_length=100, help_text='Nome del territorio')
    fk_tipo_territorio = models.ForeignKey('TipoTerritorio', verbose_name='Tipo Territorio', on_delete=models.SET_NULL, null=True)
    parent = models.ForeignKey('self', blank=True, related_name='child', help_text='Parent del Territorio', on_delete=models.SET_NULL, null=True)
    codice = models.PositiveIntegerField(help_text='Codice del Territorio', null=True)
    geometry = models.GeometryField(spatial_index=True, null=True)

    def __str__(self):
        """String for representing the Model object."""
        return self.nome

    class Meta:
        verbose_name_plural = "Territori"

class TipoTerritorio(models.Model):
    """Modello che rappresenta la tipologia di una norma"""
    nome = models.CharField(max_length=100, help_text='Tipologia di territorio')

    def __str__(self):
        """String for representing the Model object."""
        return self.nome

    class Meta:
        verbose_name_plural = "TipiTerritorio"

I am relatively new to Django and GeoDjango and I might be overlooking something. Any Idea on how to solve the migrate error?

EDIT: added 0008_territorio_geometry.py

# Generated by Django 3.0.4 on 2020-04-06 13:19

import django.contrib.gis.db.models.fields
from django.db import migrations


class Migration(migrations.Migration):

    dependencies = [
        ('map', '0007_auto_20200406_1506'),
    ]

    operations = [
        migrations.AddField(
            model_name='territorio',
            name='geometry',
            field=django.contrib.gis.db.models.fields.GeometryField(default=0, srid=4326),
            preserve_default=False,
        ),
    ]

Answer 1

You are adding the geometry field after the initial Territorio model creation, but you are not providing a default value to the field.
In order to apply this migration, Django asked you (in the terminal after the ./manage.py makemigrations part) to provide a default value manually for any existing records in the table. You must have answered 0 to that question and thus the problem arises (you have essentially added an Integer value to a Geometry field).

Since you are allowing null=True to the geometry field, the easy fix would be to:

1. Revert the migrations to the previous one (0007_auto_20200406_1506):

   ./manage.py migrate my_app 0007_auto_20200406_1506
   

2. Delete the migration file 0008_territorio_geometry.py.

3. Check the table django_migrations in your DB for the entry 0008_territorio_geometry and remove that as well (if it exists).

4. Provide a default value of None to the geometry field as follows:

   geometry = models.GeometryField(spatial_index=True, null=True, default=None)
   

5. Recreate the migration naming it as you like, and then apply it:

   ./manage.py makemigrations --name 0008_territorio_geometry
   ./manage.py migrate
   

You should be set to go :)

Answer 2

`

dependencies = [
    ('map', '0007_auto_20200406_1506'),
]

operations = [
    migrations.AddField(
        model_name='territorio',
        name='geometry',
        field=django.contrib.gis.db.models.fields.GeometryField(default=0, srid=4326),
        preserve_default=False,
    ),
]`

changes

`

dependencies = [
    ('map', '0007_auto_20200406_1506'),
]

operations = [
    migrations.AddField(
        model_name='territorio',
        name='geometry',
        field=django.contrib.gis.db.models.fields.GeometryField(default=0, srid=4326),
        preserve_default=None,
    ),
]`