Fix request parameter representation in API view

In API view, representation of a parameter defined as a sub class of
`WritableNestedSerializer` should be vary between a request and a
response. For example, `tenant` field in `IPAddressSerializer` should be
shown like following as a request body:

```
tenant: integer ...
```

while it should be shown like following as a response body:

```
tenant: {
    id: integer ...,
    url: string ...,
    name: string ...,
    slug: string ...
}
```

But in both cases, it is shown as a response body type expression. This
causes an error at sending an API request with that type value.

It is only an API view issue, API can handle a request if a request
parameter is structured as an expected request body by ignoring the
wrong expression.

This fixes the issue by replacing an implicitly used default auto schema
generator class by its sub class and returning a pseudo serializer with
'Writable' prefix at generating a request body. The reason to introduce
a new generator class is that there is no other point which can
distinguish a request and a response. It is not enough to distinguish
POST, PUT, PATCH methods from GET because former cases may return a JSON
object as a response but it is also represented as same as a request
body, causes another mismatch.

This also fixes `SerializedPKRelatedField` type field representation. It
should be shown as an array of primary keys in a request body.

Fixed #2400

CHANGELOG.md

@@ -6,6 +6,7 @@ v2.4.5 (FUTURE)
 
 ## Bug Fixes
 
+* [#2400](https://github.com/digitalocean/netbox/issues/2400) - API variable type mismatch at creating/modifying an entry
 * [#2406](https://github.com/digitalocean/netbox/issues/2406) - Remove hard-coded limit of 1000 objects from API-populated form fields
 
 ---

netbox/netbox/settings.py

@@ -275,6 +275,7 @@ RQ_QUEUES = {
 
 # drf_yasg settings for Swagger
 SWAGGER_SETTINGS = {
+    'DEFAULT_AUTO_SCHEMA_CLASS': 'utilities.custom_inspectors.NetBoxSwaggerAutoSchema',
     'DEFAULT_FIELD_INSPECTORS': [
         'utilities.custom_inspectors.NullableBooleanFieldInspector',
         'utilities.custom_inspectors.CustomChoiceFieldInspector',

netbox/utilities/custom_inspectors.py

@@ -1,10 +1,30 @@
 from drf_yasg import openapi
-from drf_yasg.inspectors import FieldInspector, NotHandled, PaginatorInspector, FilterInspector
+from drf_yasg.inspectors import FieldInspector, NotHandled, PaginatorInspector, FilterInspector, SwaggerAutoSchema
 from rest_framework.fields import ChoiceField
+from rest_framework.relations import ManyRelatedField
 from taggit_serializer.serializers import TagListSerializerField
 
 from extras.api.customfields import CustomFieldsSerializer
-from utilities.api import ChoiceField, SerializedPKRelatedField
+from utilities.api import ChoiceField, SerializedPKRelatedField, WritableNestedSerializer
+
+
+class NetBoxSwaggerAutoSchema(SwaggerAutoSchema):
+    def get_request_serializer(self):
+        serializer = super().get_request_serializer()
+
+        if serializer is not None and self.method in self.implicit_body_methods:
+            properties = {}
+            for child_name, child in serializer.fields.items():
+                if isinstance(child, (ChoiceField, WritableNestedSerializer)):
+                    properties[child_name] = None
+                elif isinstance(child, ManyRelatedField) and isinstance(child.child_relation, SerializedPKRelatedField):
+                    properties[child_name] = None
+
+            if properties:
+                writable_class = type('Writable' + type(serializer).__name__, (type(serializer),), properties)
+                serializer = writable_class()
+
+        return serializer
 
 
 class SerializedPKRelatedFieldInspector(FieldInspector):