# Polymorphic relationships

{% hint style="success" %}
This is the official documentation of the `forestadmin-agent-django` and `forestadmin-agent-flask` Python agents.
{% endhint %}

### Enable polymorphic support

Forest admin can interact with polymorphic relations by enabling the `polymorphic` option on the datasource instance.

{% tabs %}
{% tab title="my\_project.settings.py" %}

```python
# ...
FOREST_CUSTOMIZE_FUNCTION = "my_app.forest_admin.customize_agent"
FOREST_AUTO_ADD_DJANGO_DATASOURCE = False
```

{% endtab %}

{% tab title="my\_app.forest\_admin.py" %}

```python
from forestadmin.datasource_django.datasource import DjangoDatasource
from forestadmin.django_agent.agent import DjangoAgent

def customize_forest(agent: DjangoAgent):
    agent.add_datasource(DjangoDatasource(support_polymorphic_relations=True))

```

{% endtab %}
{% endtabs %}

Because Django usea a foreign key to `django_content_type` and Forest requires a string field for the type field, an enum field will automatically be created to replace the relationship to `django_content_type`. This enum field will have enum one entry per reverse relation declared with `django.contrib.contenttypes.fields.GenericRelation`.

### Tips

The `id field` and the `type field`(along with the foreign key to `django_content_type`) of the relationship are still shown. You can use them to create segment, [hide them from the agent](https://docs.forestadmin.com/developer-guide-agents-python/agent-customization/fields/import-rename-remove#renaming-and-removing-fields-and-relations) or through the front-end configuration.

### Limitations

#### Collections

**Remove collection**

When using the [remove collection customization](https://docs.forestadmin.com/developer-guide-agents-python/data-sources/getting-started/partial-imports), it's important to note a limitation regarding collections that are potential targets of polymorphic relationships. If you attempt to delete a collection that is referenced in a polymorphic relationship, an exception will be thrown with the following message:

```
Cannot remove {CollectionName} because it's a potential target of polymorphic relation {InverseRelationName}.
```

This limitation exists to prevent corruption of data relationships that depend on this collection in a polymorphic context. Before attempting deletion, ensure that the collection you want to delete is not used as a target in such a relationship before attempting the deletion.

**Rename Collection**

The [rename collection customization](https://docs.forestadmin.com/developer-guide-agents-python/data-sources/getting-started/naming-conflicts) also imposes a restriction on collections involved in polymorphic relationships. If you attempt to rename a collection that is the target of a polymorphic relationship, an exception will be thrown with the following message:

```
Cannot rename collection {CurrentName} because it's a target of a polymorphic relation '{ForeignCollectionName}.{InverseRelationName}'.
```

This limitation ensures the integrity of polymorphic relationships in your data model. Before renaming a collection, verify that it is not involved in such polymorphic relationships to avoid errors.

#### Fields

**Remove field**

When using the [remove field customization](https://docs.forestadmin.com/developer-guide-agents-python/agent-customization/fields/import-rename-remove#renaming-and-removing-fields-and-relations), it's important to note a limitation concerning fields involved in the polymorphic relationships (`foreign_key_type` and `foreign_key_id`). If you attempt to delete a field that is used in a polymorphic relationship, an exception will be thrown with the following message:

```
Cannot remove field {CollectionName}.{FieldName}, because it's implied in a polymorphic relation '{CollectionName}.{PolymorphicRelationName}'.
```

This limitation is in place to ensure the proper functioning of the polymorphic relationship. Before deleting a field, ensure that the field you want to delete is not used as a foreign key or type field in any polymorphic relationship.

**Rename field**

When using the [rename field customization](https://docs.forestadmin.com/developer-guide-agents-python/agent-customization/fields/import-rename-remove#renaming-and-removing-fields-and-relations), it's important to be aware of a limitation concerning fields involved in polymorphic relationships (`foreign_key_type` and `foreign_key_id`). If you attempt to rename a field that is used in a polymorphic relationship, an exception will be thrown with the following message:

```
Cannot rename '{CollectionName}.{FieldName}', because it's implied in a polymorphic relation '{CollectionName}.{PolymorphicRelationName}'.
```

This limitation is in place to ensure the proper functioning of polymorphic relationship. Before renaming a field, ensure that the field you want to rename is not used as a as foreign key or type field of a polymorphic relationship.

**Computed field**

When using [computed fields](https://docs.forestadmin.com/developer-guide-agents-python/agent-customization/fields/computed), a list of `dependency` fields is required. Theses fields can travels '\*toOne' relationships using ':'. However, due to the unpredictable target collection of polymorphic relationship, they cannot be used as dependencies for computed fields; an error will be thrown with the following message:

```
Dependencies over a polymorphic relations({CollectionName}.{PolymorphicRelationName}) are forbidden.
```

Another limitation exists with computed fields when they are used as `reference field`. Due to the unpredictable target collection of the polymorphic relationships, computed fields cannot be evaluated over polymorphic relations. If used as a reference field, it will not be displayed on the front-end.

When computed fields are not evaluated over polymorphic relationships, a `debug` log is generated with the following message:

```
Cannot compute computed fields over polymorphic relation {CollectionName}.{PolymorphicRelationName}.
```

#### Search (extended)

When searching within a collection that contains a polymorphic relationship, [extended searches](https://docs.forestadmin.com/developer-guide-agents-python/agent-customization/search#search-modes) will not search through the polymorphic relationships. This behavior is designed to prevent excessive resource consumption and delays in SQL queries. A `debug` log will appear to alert you about this behavior with the following message:

```
We're not searching through {CollectionName}.{PolymorphicRelationName} because it's a polymorphic relation. You can override the default search behavior with 'replace_search'.
```

And a link leading to the [replace search documentation](https://docs.forestadmin.com/developer-guide-agents-python/agent-customization/search#customization). If you understand the implications and still want to search through polymorphic relations, you can follow the [replace search documentation](https://docs.forestadmin.com/developer-guide-agents-python/agent-customization/search#customization) to override the default search behavior.