Django migration strategy for renaming a model and relationship fields

Django migration strategy for renaming a model and relationship fields

I'm planning to rename several models in an existing Django project where there are many other models that have foreign key relationships to the models I would like to rename. I'm fairly certain this will require multiple migrations, but I'm not sure of the exact procedure.
Let's say I start out with the following models within a Django app called myapp:
class Foo(models.Model):
    name = models.CharField(unique=True, max_length=32)
    description = models.TextField(null=True, blank=True)


class AnotherModel(models.Model):
    foo = models.ForeignKey(Foo)
    is_awesome = models.BooleanField()


class YetAnotherModel(models.Model):
    foo = models.ForeignKey(Foo)
    is_ridonkulous = models.BooleanField()

I want to rename the Foo model because the name doesn't really make sense and is causing confusion in the code, and Bar would make for a much clearer name. 
From what I have read in the Django development documentation, I'm assuming the following migration strategy:
Step 1
Modify models.py:
class Bar(models.Model):  # <-- changed model name
    name = models.CharField(unique=True, max_length=32)
    description = models.TextField(null=True, blank=True)


class AnotherModel(models.Model):
    foo = models.ForeignKey(Bar)  # <-- changed relation, but not field name
    is_awesome = models.BooleanField()


class YetAnotherModel(models.Model):
    foo = models.ForeignKey(Bar)  # <-- changed relation, but not field name
    is_ridonkulous = models.BooleanField()

Note the AnotherModel field name for foo doesn't change, but the relation is updated to the Bar model. My reasoning is that I shouldn't change too much at once and that if I changed this field name to bar I would risk losing the data in that column.
Step 2
Create an empty migration:
python manage.py makemigrations --empty myapp

Step 3
Edit the Migration class in the migration file created in step 2 to add the RenameModel operation to the operations list:
class Migration(migrations.Migration):

    dependencies = [
        ('myapp', '0001_initial'),
    ]

    operations = [
        migrations.RenameModel('Foo', 'Bar')
    ]

Step 4
Apply the migration:
python manage.py migrate

Step 5
Edit the related field names in models.py:
class Bar(models.Model):
    name = models.CharField(unique=True, max_length=32)
    description = models.TextField(null=True, blank=True)


class AnotherModel(models.Model):
    bar = models.ForeignKey(Bar)  # <-- changed field name
    is_awesome = models.BooleanField()


class YetAnotherModel(models.Model):
    bar = models.ForeignKey(Bar)  # <-- changed field name
    is_ridonkulous = models.BooleanField()

Step 6
Create another empty migration:
python manage.py makemigrations --empty myapp

Step 7
Edit the Migration class in the migration file created in step 6 to add the RenameField operation(s) for any related field names to the operations list:
class Migration(migrations.Migration):

    dependencies = [
        ('myapp', '0002_rename_fields'),  # <-- is this okay?
    ]

    operations = [
        migrations.RenameField('AnotherModel', 'foo', 'bar'),
        migrations.RenameField('YetAnotherModel', 'foo', 'bar')
    ]

Step 8
Apply the 2nd migration:
python manage.py migrate


Aside from updating the rest of the code (views, forms, etc.) to reflect the new variable names, is this basically how the new migration functionality would work?
Also, this seems like a lot of steps. Can the migration operations be condensed in some way?
Thanks!

Solutions/Answers:

Answer 1:

So when I tried this, it seems you can condense Step 3 - 7:

class Migration(migrations.Migration):

    dependencies = [
        ('myapp', '0001_initial'), 
    ]

    operations = [
        migrations.RenameModel('Foo', 'Bar'),
        migrations.RenameField('AnotherModel', 'foo', 'bar'),
        migrations.RenameField('YetAnotherModel', 'foo', 'bar')
    ]

You may get some errors if you don't update the names where it's imported e.g. admin.py and even older migration files (!).

Update: As ceasaro mentions, newer versions of Django are usually able to detect and ask if a model is renamed. So try manage.py makemigrations first and then check the migration file.

Answer 2:

At first, I thought that Fiver's method worked for me because the migration worked well until step 4. However, the implicit changes 'ForeignKeyField(Foo)' into 'ForeignKeyField(Bar)' was not related in any migrations. This is why migration failed when I wanted to rename relationship fields (step 5-8).
This might be due to the fact that my 'AnotherModel' and 'YetAnotherModel' are dispatched in other apps in my case.

So I managed to rename my models and relationship fields doing following below steps:

I adapted the method from this and particularly the trick of otranzer.

So like Fiver let's say we have in myapp:

class Foo(models.Model):
    name = models.CharField(unique=True, max_length=32)
    description = models.TextField(null=True, blank=True)

And in myotherapp:

class AnotherModel(models.Model):
    foo = models.ForeignKey(Foo)
    is_awesome = models.BooleanField()


class YetAnotherModel(models.Model):
    foo = models.ForeignKey(Foo)
    is_ridonkulous = models.BooleanField()

Step 1:

Transform every OneToOneField(Foo) or ForeignKeyField(Foo) into IntegerField(). (This will keep the id of related Foo object as value of the integerfield).

class AnotherModel(models.Model):
    foo = models.IntegerField()
    is_awesome = models.BooleanField()

class YetAnotherModel(models.Model):
    foo = models.IntegerField()
    is_ridonkulous = models.BooleanField()

Then

python manage.py makemigrations

python manage.py migrate

Step 2: (Like step 2-4 from Fiver)

Change the model name

class Bar(models.Model):  # <-- changed model name
    name = models.CharField(unique=True, max_length=32)
    description = models.TextField(null=True, blank=True)

Create an empty migration:

python manage.py makemigrations --empty myapp

Then edit it like:

class Migration(migrations.Migration):

    dependencies = [
        ('myapp', '0001_initial'),
    ]

    operations = [
        migrations.RenameModel('Foo', 'Bar')
    ]

Eventually

python manage.py migrate

Step 3:

Transform Back your IntegerField() into their previous ForeignKeyField or OneToOneField but with the new Bar Model. (The previous integerfield was storing the id, so django understand that and reestablish the connection, which is cool.)

class AnotherModel(models.Model):
    foo = models.ForeignKey(Bar)
    is_awesome = models.BooleanField()

class YetAnotherModel(models.Model):
    foo = models.ForeignKey(Bar)
    is_ridonkulous = models.BooleanField()

Then do:

python manage.py makemigrations 

Very importantly, at this step you have to modify every new migrations and add the dependency on the RenameModel Foo-> Bar migrations.
So if both AnotherModel and YetAnotherModel are in myotherapp the created migration in myotherapp must look like this:

class Migration(migrations.Migration):

    dependencies = [
        ('myapp', '00XX_the_migration_of_myapp_with_renamemodel_foo_bar'),
        ('myotherapp', '00xx_the_migration_of_myotherapp_with_integerfield'),
    ]

    operations = [
        migrations.AlterField(
            model_name='anothermodel',
            name='foo',
            field=models.ForeignKey(to='myapp.Bar'),
        ),
        migrations.AlterField(
            model_name='yetanothermodel',
            name='foo',
            field=models.ForeignKey(to='myapp.Bar')
        ),
    ]

Then

python manage.py migrate

Step 4:

Eventually you can rename your fields

class AnotherModel(models.Model):
    bar = models.ForeignKey(Bar) <------- Renamed fields
    is_awesome = models.BooleanField()


class YetAnotherModel(models.Model):
    bar = models.ForeignKey(Bar) <------- Renamed fields
    is_ridonkulous = models.BooleanField()

and then do automatic renaming

python manage.py makemigrations

(django should ask you if you actually renamed the modelname, say yes)

python manage.py migrate

And that's it!

This works on Django1.8

Answer 3:

I needed to do the same thing. I changed the model all at once (i.e., step 1 and step 5 together). Then created a schema migration but edited it to be this:

class Migration(SchemaMigration):
    def forwards(self, orm):
        db.rename_table('Foo','Bar')

    def backwards(self, orm):
        db.rename_table('Bar','Foo')

This worked perfectly. All my existing data showed up, all the other tables referenced Bar fine.

from here: https://hanmir.wordpress.com/2012/08/30/rename-model-django-south-migration/

Answer 4:

For Django 1.10, I managed to change two model class names (including a ForeignKey, and with data) by simply running Makemigrations, and then Migrate for the app. For the Makemigrations step, I had to confirm that I wanted to change the table names. Migrate changed the names of the tables without a problem.

Then I changed the name of the ForeignKey field to match, and again was asked by Makemigrations to confirm that I wanted to change the name. Migrate than made the change.

So I took this in two steps without any special file editing. I did get errors at first because I forgot to change the admin.py file, as mentioned by @wasibigeek.

Answer 5:

I also faced the problem as v.thorey described and found that his approach is very useful but can be condensed into fewer steps which are actually step 5 to 8 as Fiver described without step 1 to 4 except that step 7 needs to be changed as my below step 3. The overall steps are as follow:

Step 1: Edit the related field names in models.py

class Bar(models.Model):
    name = models.CharField(unique=True, max_length=32)
    description = models.TextField(null=True, blank=True)


class AnotherModel(models.Model):
    bar = models.ForeignKey(Bar)  # <-- changed field name
    is_awesome = models.BooleanField()


class YetAnotherModel(models.Model):
    bar = models.ForeignKey(Bar)  # <-- changed field name
    is_ridonkulous = models.BooleanField()

Step 2: Create an empty migration

python manage.py makemigrations --empty myapp

Step 3: Edit the Migration class in the migration file created in Step 2

class Migration(migrations.Migration):

dependencies = [
    ('myapp', '0001_initial'), 
]

operations = [
    migrations.AlterField(
        model_name='AnotherModel',
        name='foo',
        field=models.IntegerField(),
    ),
    migrations.AlterField(
        model_name='YetAnotherModel',
        name='foo',
        field=models.IntegerField(),
    ),
    migrations.RenameModel('Foo', 'Bar'),
    migrations.AlterField(
        model_name='AnotherModel',
        name='foo',
        field=models.ForeignKey(to='myapp.Bar'),
    ),
    migrations.AlterField(
        model_name='YetAnotherModel',
        name='foo',
        field=models.ForeignKey(to='myapp.Bar'),
    ),
    migrations.RenameField('AnotherModel', 'foo', 'bar'),
    migrations.RenameField('YetAnotherModel', 'foo', 'bar')
]

Step 4: Apply the migration

python manage.py migrate

Done

P.S. I've tried this approach on Django 1.9

Answer 6:

I am using Django version 1.9.4

I have follow the following steps:-

I have just rename the model oldName to NewName
Run python manage.py makemigrations. It will ask you for
Did you rename the appname.oldName model to NewName? [y/N] select Y

Run python manage.py migrate and it will ask you for

The following content types are stale and need to be deleted:

appname | oldName
appname | NewName

Any objects related to these content types by a foreign key will also
be deleted. Are you sure you want to delete these content types?
If you're unsure, answer 'no'.

Type 'yes' to continue, or 'no' to cancel: Select No

It rename and migrate all existing data to new named table for me.

Answer 7:

Unfortunately, I found problems (each django 1.x) with rename migration which leave old table names in the database.

Django doesn't even try anything on the old table, just rename his own model.
The same problem with foreign keys, and indices in general - changes there are not tracked properly by Django.

The simplest solution (workaround):

class Foo(models.Model):
     name = models.CharField(unique=True, max_length=32)
     ...
Bar = Foo  # and use Bar only

The real solution (an easy way to switch all
indices, constraints, triggers, names, etc in 2 commits, but rather for smaller tables):

commit A:

  1. create the same model as the old one
# deprecated - TODO: TO BE REMOVED
class Foo(model.Model):
    ...

class Bar(model.Model):
    ...
  1. switch code to work with new model Bar only.
    (including all relations on the schema)

In migration prepare RunPython, which copy data from Foo to Bar
(including id of Foo)

  1. optional optimization (if needed for greater tables)

commit B: (no rush, do it when an entire team is migrated)

  1. safe drop of the old model Foo

further cleanup:

  • squash on migrations

bug in Django:

Answer 8:

Just wanted to confirm and add upon ceasaro comment. Django 2.0 seems to do this automatically now.

I'm on Django 2.2.1, all I had to do what to rename the model and run makemigrations.

Here it asks if I had renamed the specific class from A to B, i chose yes and ran migrate and all seems to work.

Note I did not rename the old model name in any files inside the project/migrations folder.

Answer 9:

I needed to rename a couple of tables. But only one model rename was noticed by Django. That happened because Django iterates over added, then removed models. For each pair it checks if they're of the same app and have identical fields. Only one table had no foreign keys to tables to be renamed (foreign keys contain model class name, as you remember). In other words, only one table had no field changes. That's why it was noticed.

So, the solution is to rename one table at a time, changing model class name in models.py, possibly views.py, and making a migration. After that inspect your code for other references (model class names, related (query) names, variable names). Make a migration, if needed. Then, optionally combine all these migrations into one (make sure to copy imports as well).

Answer 10:

I would make @ceasaro words, mine on his comment on this answer.

Newer versions of Django can detect changes and ask about what was done.
I also would add that Django might mix the order of execution of some migration commands.

It would be wise to apply small changes and run makemigrations and migrate and if the error occurs the migration file can be edited.

Some lines order of execution can be changed to avoid erros.

Answer 11:

If you are using a good IDE like PyCharm you can right click on the model name and do a refactor -> rename. This saves you the trouble of going through all your code that references the model. Then run makemigrations and migrate. Django 2+ will simply confirm name change.

Answer 12:

I upgraded Django from version 10 to version 11:

sudo pip install -U Django

(-U for "upgrade") and it solved the problem.

References