Re: MySQL accepts 0 for a primary key but Django does not

Hello Derek,

There's no setting but this is controlled by the allows_auto_pk_0 feature flag [0].

Database feature are set to the default database configurations so Django can

minimized the number of introspection queries required to work appropriately

each time a connection is opened.

In order to override it I suggest you create a subclass of django.db.backends.mysql.base.DatabaseWrapper in

a custom foo.bar.base module and set feature_class to a .features.DatabaseFeatures[1]

subclass that sets the allows_auto_pk_0 flag to True.

e.g.

#foo/bar/base.py

from django.db.backends.mysql.base import DatabaseWrapper as BaseDatabaseWrapper

from django.db.backends.mysql.features import DatabaseFeatures as BaseDatabaseFeatures

class DatabaseFeatures(BaseDatabaseFeatures):

    allows_auto_pk_0 = True

class DatabaseWrapper(BaseDatabaseWrapper):

    features_class = DatabaseFeatures

Then you'll want to point your DATABASES.ENGINE to 'foo.bar' instead of 'django.db.backends.mysql'.

Keep in mind that Django expects

1. A .base submodule [2]

2. A class named DatabaseWrapper [3]

The foo.bar module path can be renamed to whatever you want.

Cheers,

[0] https://github.com/django/django/blob/e817ae74da0e515db31907ebcb2d00bcf7c3f5bc/django/db/backends/mysql/features.py#L27

[1] https://github.com/django/django/blob/e817ae74da0e515db31907ebcb2d00bcf7c3f5bc/django/db/backends/mysql/base.py#L184

[2] https://github.com/django/django/blob/e817ae74da0e515db31907ebcb2d00bcf7c3f5bc/django/db/utils.py#L110

[3] https://github.com/django/django/blob/e817ae74da0e515db31907ebcb2d00bcf7c3f5bc/django/db/utils.py#L203

Le vendredi 28 décembre 2018 07:47:31 UTC-5, Derek a écrit :

I am working with some legacy data and need to preserve the existing record ID's which, in some tables, include the value of 0 for their auto-increment field.

I have updated the configuration file for MySQL such that the sql_mode is set to include 'NO_AUTO_VALUE_ON_ZERO'.  

I can check that this works by running the following test inside the MySQL shell:

create table number (number int not null auto_increment primary key); insert into number(number) values (0); select * from number; drop table number;

+--------+

| number |

+--------+

|      0 |

+--------+

1 row in set (0,00 sec)

However, when I try this approach with one of my existing models (in the Django shell) I get an error:

from myapp.models import MyModel

MyModel.objects.create(pk=0, direction=1, code='UNK')

Traceback (most recent call last):

  File "<console>", line 1, in <module>

  File "/home/gamesbook/,virtualenvs/proj/local/lib/python2.7/site-packages/django/db/models/manager.py", line 157, in create

    return self.get_queryset().create(**kwargs)

  File "/home/gamesbook/,virtualenvs/proj/local/lib/python2.7/site-packages/django/db/models/query.py", line 322, in create

    obj.save(force_insert=True, using=self.db)

  File "/home/gamesbook/,virtualenvs/proj/local/lib/python2.7/site-packages/django/db/models/base.py", line 545, in save

    force_update=force_update, update_fields=update_fields)

  File "/home/gamesbook/,virtualenvs/proj/local/lib/python2.7/site-packages/django/db/models/base.py", line 573, in save_base

    updated = self._save_table(raw, cls, force_insert, force_update, using, update_fields)

  File "/home/gamesbook/,virtualenvs/proj/local/lib/python2.7/site-packages/django/db/models/base.py", line 654, in _save_table

    result = self._do_insert(cls._base_manager, using, fields, update_pk, raw)

  File "/home/gamesbook/,virtualenvs/proj/local/lib/python2.7/site-packages/django/db/models/base.py", line 687, in _do_insert

    using=using, raw=raw)

  File "/home/gamesbook/,virtualenvs/proj/local/lib/python2.7/site-packages/django/db/models/manager.py", line 232, in _insert

    return insert_query(self.model, objs, fields, **kwargs)

  File "/home/gamesbook/,virtualenvs/proj/local/lib/python2.7/site-packages/django/db/models/query.py", line 1514, in insert_query

    return query.get_compiler(using=using).execute_sql(return_id)

  File "/home/gamesbook/,virtualenvs/proj/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 902, in execute_sql

    for sql, params in self.as_sql():

  File "/home/gamesbook/,virtualenvs/proj/local/lib/python2.7/site-packages/django/db/models/sql/compiler.py", line 860, in as_sql

    for obj in self.query.objs

  File "/home/gamesbook/,virtualenvs/proj/local/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 350, in get_db_prep_save

    prepared=False)

  File "/home/gamesbook/,virtualenvs/proj/local/lib/python2.7/site-packages/django/db/models/fields/__init__.py", line 607, in get_db_prep_value

    value = connection.ops.validate_autopk_value(value)

  File "/home/gamesbook/,virtualenvs/proj/local/lib/python2.7/site-packages/django/db/backends/mysql/base.py", line 336, in validate_autopk_value

    raise ValueError('The database backend does not accept 0 as a '

ValueError: The database backend does not accept 0 as a value for AutoField.

Is there a setting I need to change such that Django does not raise this error and allows the PK to be zero?

Thanks

Derek

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