#28000: Migration forces "DROP DEFAULT" SQL
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Reporter: Matteo Pietro Russo | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 1.9
Severity: Normal | Keywords:
Triage Stage: Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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If i consider to modify a column (ChaField) to add a default value as
follow:
from django.db import models
class PersonModel(models.Model):
nickname = models.CharField(default="noname", max_length=100,
null=False)
makemigration insists on creating a new migration for this change.
However, the migration on MYSQL shows:
BEGIN;
ALTER TABLE "core_personmodel" ALTER "nickname" SET DEFAULT 'noname';
ALTER TABLE "core_personmodel" ALTER "nickname" DROP DEFAULT;
COMMIT;
I think there is a mistake at line 735 in
django/db/backends/base/schema.py
{{{
# Drop the default if we need to
# (Django usually does not use in-database defaults)
if needs_database_default:
sql = self.sql_alter_column % {
"table": self.quote_name(model._meta.db_table),
"changes": self.sql_alter_column_no_default % {
"column": self.quote_name(new_field.column),
}
}
self.execute(sql)
}}}
If I "needs_database_default", why we need to drop default
(sql_alter_column_no_default)? I read we use it to prevent extraneous DROP
DEFAULT statements (an example is LONGTEXT in MySQL) because if database
is able to use default we need to avoid to drop it.
--
Ticket URL: <https://code.djangoproject.com/ticket/28000>
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