On Tue, May 14, 2013 at 12:20 PM, Giorgos Kontogiorgakis
<shortgeorge...@yahoo.com> wrote:
> Hi,
>
> i have this model
>
> class Linkmap(models.Model):
> vpathid = models.IntegerField(db_column='VPathID') # Field name made
> lowercase.
> interfacein = models.CharField(max_length=20L, db_column='InterfaceIn')
> # Field name made lowercase.
> #Every Link belongs to a LinkMap
> #links = models.ForeignKey(Links)
> interfaceout = models.CharField(max_length=20L,
> db_column='InterfaceOut') # Field name made lowercase.
> #Every Vpath composes a LinkMap
> vpaths = models.ForeignKey(Vpaths)
> hopcounter = models.BigIntegerField(null=True, db_column='HopCounter',
> blank=True) # Field name made lowercase.
> def __unicode__(self):
> return 'VPathID %s , HopCounter %s' %
> (self.vpathid,self.hopcounter)
> class Meta:
> db_table = 'LinkMap'
>
>
> when i uncommented links = models.ForeignKey(Links)
>
> and tried to migrate i got this exeption:
>
> root@Roronoa:/home/roronoa/Desktop/webinterface/mysite# ./manage.py migrate
> myapp
> Running migrations for myapp:
> - Migrating forwards to 0048_auto__add_field_linkmap_links.
> > myapp:0048_auto__add_field_linkmap_links
> FailedDryRun: ! Error found during dry run of
> '0048_auto__add_field_linkmap_links'! Aborting.
> Traceback (most recent call last):
> File
> "/usr/local/lib/python2.7/dist-packages/South-0.7.6-py2.7.egg/south/migration/migrators.py",
> line 175, in _run_migration
> migration_function()
> File
> "/usr/local/lib/python2.7/dist-packages/South-0.7.6-py2.7.egg/south/migration/migrators.py",
> line 57, in <lambda>
> return (lambda: direction(orm))
> File
> "/home/roronoa/Desktop/webinterface/mysite/myapp/migrations/0048_auto__add_field_linkmap_links.py",
> line 14, in forwards
> keep_default=False)
> File
> "/usr/local/lib/python2.7/dist-packages/South-0.7.6-py2.7.egg/south/db/generic.py",
> line 44, in _cache_clear
> return func(self, table, *args, **opts)
> File
> "/usr/local/lib/python2.7/dist-packages/South-0.7.6-py2.7.egg/south/db/generic.py",
> line 402, in add_column
> sql = self.column_sql(table_name, name, field)
> File
> "/usr/local/lib/python2.7/dist-packages/South-0.7.6-py2.7.egg/south/db/generic.py",
> line 688, in column_sql
> default = field.get_db_prep_save(default,
> connection=self._get_connection())
> File
> "/usr/local/lib/python2.7/dist-packages/django/db/models/fields/related.py",
> line 1047, in get_db_prep_save
> connection=connection)
> File
> "/usr/local/lib/python2.7/dist-packages/django/db/models/fields/__init__.py",
> line 304, in get_db_prep_save
> prepared=False)
> File
> "/usr/local/lib/python2.7/dist-packages/django/db/models/fields/__init__.py",
> line 549, in get_db_prep_value
> value = connection.ops.validate_autopk_value(value)
> File
> "/usr/local/lib/python2.7/dist-packages/django/db/backends/mysql/base.py",
> line 288, 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.
>
>
>
> I can't do nothing as many tries i did!I not that experienced in South and
> Django,just started to use them!Any help would be appriciated!
>
You wrote the answer in your code*:
#Every Link belongs to a LinkMap
links = models.ForeignKey(Links)
When you run the migration, it has no possible value to give the
existing LinkMaps, and the database complains.
If you instead initially define the foreign key with null=True,
blank=True, then the migration can complete - it knows what value to
use, NULL. You can then add a datamigration to add in the necessary
data, so that none of the rows have NULL as a value, and then finally
a second schema migration to take away the null/blank constraints.
Cheers
Tom
* Although your logic is a little off, by putting the foreign key on
the LinkMap, you are saying each LinkMap has exactly one Link. I think
the foreign key should be on Link, so that each Link has exactly one
LinkMap
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