#28065: makemigrations creates unnecessary migration for adding related_name to
ForeignKey
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Reporter: Cameron Dawson | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 1.11
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 you just add a {{{related_name}}} to an existing foreign key, it will
require a migration which then drops and re-creates the foreign key. This
is a non-DB, {{{meta}}} change only and shouldn't create a migration.
With Models:
{{{
class Job(models.Model):
id = models.BigAutoField(primary_key=True)
name = models.CharField(max_length=30, null=True)
class JobDetail(models.Model):
id = models.BigAutoField(primary_key=True)
job = models.ForeignKey(Job)
}}}
my initial migration is:
{{{
operations = [
migrations.CreateModel(
name='Job',
fields=[
('id', models.BigAutoField(primary_key=True,
serialize=False)),
('name', models.CharField(max_length=30, null=True)),
],
),
migrations.CreateModel(
name='JobDetail',
fields=[
('id', models.BigAutoField(primary_key=True,
serialize=False)),
('job',
models.ForeignKey(on_delete=django.db.models.deletion.CASCADE,
to='polls.Job')),
],
),
]
}}}
Then if I modify the {{{JobDetail}}} model ForeignKey as follows:
{{{
job = models.ForeignKey(Job, related_name="job_details")
}}}
and run {{{makemigrations}}}, I end up with a migration:
{{{
operations = [
migrations.AlterField(
model_name='jobdetail',
name='job',
field=models.ForeignKey(on_delete=django.db.models.deletion.CASCADE,
related_name='job_details', to='polls.Job'),
),
]
}}}
The {{{CREATE_INDEX}}} for both migrations is identical:
{{{
CREATE INDEX "polls_jobdetail_job_id_5561ba44" ON "polls_jobdetail"
("job_id");
}}}
We need to work around it with {{{migrations.RunSQL.noop}}} because the
tables in our actual application are really large and dropping the index
and re-creating is very expensive.
--
Ticket URL: <https://code.djangoproject.com/ticket/28065>
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