#28065: makemigrations creates unnecessary migration for adding related_name to
ForeignKey
--------------------------------+--------------------------------------
Reporter: Cameron Dawson | Owner: nobody
Type: Bug | Status: new
Component: Migrations | Version: 1.11
Severity: Normal | Resolution:
Keywords: | Triage Stage: Unreviewed
Has patch: 0 | Needs documentation: 0
Needs tests: 0 | Patch needs improvement: 0
Easy pickings: 0 | UI/UX: 0
--------------------------------+--------------------------------------
Description changed by Cameron Dawson:
Old description:
> 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.
New description:
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.
This is with MySQL.
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}}} result in {{{sqlmigrate}}} 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#comment:2>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.
--
You received this message because you are subscribed to the Google Groups
"Django updates" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to [email protected].
To post to this group, send email to [email protected].
To view this discussion on the web visit
https://groups.google.com/d/msgid/django-updates/062.8bb267346005068b477c0561449ff9c7%40djangoproject.com.
For more options, visit https://groups.google.com/d/optout.
