#35129: Support customize ForeignKey DDL when db_constraint=False
-------------------------------------+-------------------------------------
Reporter: elonzh | Owner: nobody
Type: | Status: new
Uncategorized |
Component: Database | Version: 5.0
layer (models, ORM) |
Severity: Normal | Keywords:
Triage Stage: | Has patch: 0
Unreviewed |
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
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Sometimes we want to join tables without foreignkeys, so we define a
ForeignKey field with db_constraint=False to achieve this.
For example:
{{{
class Journal(Model):
issn = models.CharField(max_length=9, primary_key=True)
name = models.CharField(max_length=255)
class Biblio(Model):
# There already exists a field called issn in the Biblio model
# issn = models.CharField(max_length=50, default="", blank=True)
journal = models.ForeignKey(
Journal,
related_name="+",
db_column="issn",
db_constraint=False,
db_index=False,
on_delete=models.DO_NOTHING,
default="",
blank=True,
max_length=50,
)
}}}
In this example, we define a journal field from issn field and we want to
do a fake migration.
But the migratation will generate DDL like this:
{{{
--
-- Remove field issn from biblio
--
ALTER TABLE `userlibrary_biblio` DROP COLUMN `issn`;
--
-- Add field issn_record to biblio
--
ALTER TABLE `userlibrary_biblio` ADD COLUMN `issn` varchar(9) DEFAULT ''
NOT NULL;
ALTER TABLE `userlibrary_biblio` ALTER COLUMN `issn` DROP DEFAULT;
}}}
which is kind of awkward because that means Django will force max_length=9
and this is not we want.
--
Ticket URL: <https://code.djangoproject.com/ticket/35129>
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