Hi Simon
Much appreciated.
However, I am obviously doing something wrong. If I save that code into a
file called "base.py" stored in my 'custom' app, and then change my
settings file to have:
DATABASES = {
'default': {
'ENGINE': 'custom.base', # WAS: 'django.db.backends.mysql',
'NAME': DB_NAME,
'USER': DB_USER,
'PASSWORD': DB_PWORD,
'HOST': '',
'PORT': '',
}
}
Then I get this error on startup:
Traceback (most recent call last):
File "manage.py", line 14, in <module>
execute_from_command_line(sys.argv)
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/core/management/__init__.py",
line 399, in execute_from_command_line
utility.execute()
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/core/management/__init__.py",
line 392, in execute
self.fetch_command(subcommand).run_from_argv(self.argv)
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/core/management/base.py",
line 242, in run_from_argv
self.execute(*args, **options.__dict__)
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/core/management/base.py",
line 280, in execute
translation.activate('en-us')
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/utils/translation/__init__.py",
line 130, in activate
return _trans.activate(language)
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/utils/translation/trans_real.py",
line 188, in activate
_active.value = translation(language)
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/utils/translation/trans_real.py",
line 177, in translation
default_translation = _fetch(settings.LANGUAGE_CODE)
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/utils/translation/trans_real.py",
line 159, in _fetch
app = import_module(appname)
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/utils/importlib.py",
line 40, in import_module
__import__(name)
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/massadmin/__init__.py",
line 28, in <module>
from django.contrib import admin
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/contrib/admin/__init__.py",
line 6, in <module>
from django.contrib.admin.sites import AdminSite, site
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/contrib/admin/sites.py",
line 4, in <module>
from django.contrib.admin.forms import AdminAuthenticationForm
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/contrib/admin/forms.py",
line 6, in <module>
from django.contrib.auth.forms import AuthenticationForm
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/contrib/auth/forms.py",
line 17, in <module>
from django.contrib.auth.models import User
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/contrib/auth/models.py",
line 48, in <module>
class Permission(models.Model):
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/db/models/base.py",
line 96, in __new__
new_class.add_to_class('_meta', Options(meta, **kwargs))
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/db/models/base.py",
line 264, in add_to_class
value.contribute_to_class(cls, name)
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/db/models/options.py",
line 124, in contribute_to_class
self.db_table = truncate_name(self.db_table,
connection.ops.max_name_length())
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/db/__init__.py",
line 34, in __getattr__
return getattr(connections[DEFAULT_DB_ALIAS], item)
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/db/utils.py",
line 198, in __getitem__
backend = load_backend(db['ENGINE'])
File
"/home/gamesbook/.virtualenvs/s2s/local/lib/python2.7/site-packages/django/db/utils.py",
line 131, in load_backend
raise ImproperlyConfigured(error_msg)
django.core.exceptions.ImproperlyConfigured: 'custom.base' isn't an
available database backend.
Try using 'django.db.backends.XXX', where XXX is one of:
u'mysql', u'oracle', u'postgresql_psycopg2', u'sqlite3'
Any idea what I have missed?
Thanks
Derek
On Friday, 28 December 2018 16:20:33 UTC+2, Simon Charette wrote:
>
> 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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