Friday, December 28, 2018

MySQL accepts 0 for a primary key but Django does not

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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