Extending Models¶

Below is a list of tasks to consider when adding a new field to a core model.

1. Generate and run database migrations¶

Django migrations are used to express changes to the database schema. In most cases, Django can generate these automatically, however very complex changes may require manual intervention. Always remember to specify a short but descriptive name when generating a new migration.

Warning

Assert that you have installed Nautobot in your development environment using poetry install so that changes you make to migrations will apply to the source tree!

$ nautobot-server makemigrations <app> -n <name>
$ nautobot-server migrate

Where possible, try to merge related changes into a single migration. For example, if three new fields are being added to different models within an app, these can be expressed in the same migration. You can merge a new migration with an existing one by combining their operations lists.

Note

Migrations can only be merged within a release. Once a new release has been published, its migrations cannot be altered (other than for the purpose of correcting a bug).

2. Add validation logic to `clean()`¶

If the new field introduces additional validation requirements (beyond what's included with the field itself), implement them in the model's clean() method. Remember to call the model's original method using super() before or after your custom validation as appropriate:

class Foo(models.Model):

    def clean(self):

        super().clean()

        # Custom validation goes here
        if self.bar is None:
            raise ValidationError()

3. Add CSV helpers¶

Add the name of the new field to csv_headers and included a CSV-friendly representation of its data in the model's to_csv() method. These will be used when exporting objects in CSV format.

4. Update relevant querysets¶

If you're adding a relational field (e.g. ForeignKey) and intend to include the data when retrieving a list of objects, be sure to include the field using prefetch_related() as appropriate. This will optimize the view and avoid extraneous database queries.

5. Update API serializer¶

Extend the model's API serializer in <app>.api.serializers to include the new field. In most cases, it will not be necessary to also extend the nested serializer, which produces a minimal representation of the model.

6. Add field to forms¶

Extend any forms to include the new field as appropriate. Common forms include:

Credit/edit - Manipulating a single object
Bulk edit - Performing a change on many objects at once
CSV import - The form used when bulk importing objects in CSV format
Filter - Displays the options available for filtering a list of objects (both UI and API)

7. Extend object filter set¶

If the new field should be filterable, add it to the FilterSet for the model. If the field should be searchable, remember to reference it in the FilterSet's SearchFilter definition.

All filtersets should inherit from BaseFilterSet or NautobotFilterSet as appropriate to the scope of the model's functionality.

8. Add column to object table¶

If the new field will be included in the object list view, add a column to the model's table. For simple fields, adding the field name to Meta.fields will be sufficient. More complex fields may require declaring a custom column.

9. Update the UI templates¶

Edit the object's view template to display the new field. There may also be a custom add/edit form template that needs to be updated.

10. Validate the new field in GraphQL¶

If the model is already part of the GraphQL schema, the new field will be included automatically. Validate that the new field is rendering properly in GraphQL. If the field is not compatible with GraphQL or shouldn't be included in GraphQL it's possible to exclude a specific field in the GraphQL Type Object associated with this specific model. You can refer to the graphene-django documentation for additional information.

Note that if you're using the convert_django_field registry to override the default GraphQL representation for any field type, this override must be registered within the relevant app's ready() function, rather than at module import time.

11. Create/extend test cases¶

Create or extend the relevant test cases to verify that the new field and any accompanying validation logic perform as expected. This is especially important for relational fields. Nautobot incorporates various test suites, including:

API serializer/view tests
Filter tests
Form tests
Model tests
View tests

Be diligent to ensure all of the relevant test suites are adapted or extended as necessary to test any new functionality.

12. Update the model's documentation¶

Each model has a dedicated page in the documentation, at models/<app>/<model>.md. Update this file to include any relevant information about the new field.

Note that this documentation page will be accessible through the web UI via a "question mark" icon on the corresponding model create/edit page.