Bug related to the ViewSet.action attribute

[EXG1O]

While working on a project, I came across an interesting bug that seems to have existed for a long time and fixing it is extremely straightforward.

In the DRF documentation, there’s a section titled "Introspecting ViewSet actions". The code example provided there doesn't work.

The issue arises in the ViewSetMixin.initialize_request method. Here, we call the parent method initialize_request, which in turn invokes the methods get_parsers, get_authenticators and get_content_negotiator to create a Request instance. However, only after creating the Request instance is the action attribute assigned to the class.

As a result, if you try to use the action attribute in the get_parsers, get_authenticators or get_content_negotiator methods, you will encounter an error:

AttributeError: 'UserViewSet' object has no attribute 'action'

The ViewSetMixin.initialize_request method can be fixed like this:

def initialize_request(self, request, *args, **kwargs):
    """
    Set the `.action` attribute on the view, depending on the request method.
    """
    method = request.method.lower()
    if method == 'options':
        # This is a special case as we always provide handling for the
        # options method in the base `View` class.
        # Unlike the other explicitly defined actions, 'metadata' is implicit.
        self.action = 'metadata'
    else:
        self.action = self.action_map.get(method)
    return super().initialize_request(request, *args, **kwargs)

[browniebroke]

I found this issue which asked something similar. I don't think of this as a bug, rather a limitation of the current implementation. DRF chose to initialize the request before doing anything else, and the methods you mention are used to built the request.

The method attribute doesn't exists on the DRF Request class, so I assume it's proxied to the Django HttpRequest. In theory your suggestion should work, but conceptually, it feels wrong to lookup the action before we've initialized the DRF Request.

PS: as per the contributing page, we try to minimise changes in DRF:

At this point in its lifespan we consider Django REST framework to be feature-complete. We focus on pull requests that track the continued development of Django versions, and generally do not accept new features or code formatting changes.

[EXG1O]

If we look at it from a conceptual perspective, you’re right. However in that case, we should update the section "Introspecting ViewSet actions" to avoid similar discussions in the future and save DRF users time.

I suggest update this section like this:

## Introspecting ViewSet actions

During dispatch, the following attributes are available on the `ViewSet`.

* `basename` - the base to use for the URL names that are created.
* `action` - the name of the current action (e.g., `list`, `create`).
* `detail` - boolean indicating if the current action is configured for a list or detail view.
* `suffix` - the display suffix for the viewset type - mirrors the `detail` attribute.
* `name` - the display name for the viewset. This argument is mutually exclusive to `suffix`.
* `description` - the display description for the individual view of a viewset.

You may inspect these attributes to adjust behavior based on the current action.

**Note**: don`t use the `action` attribute in the `get_parsers`, `get_authenticators` or `get_content_negotiator` methods, otherwise you will get an `AttributeError` error.

[EXG1O]

I created an issue, because I haven't received an answer for a long time.