Unable to expand writable related fields on POST

[BerniWittmann]

I try to create an object via a POST request. This works very well, now to my problem:

I want the response to have the field expanded by default (in the direct response to the post request).
When trying this either via http://localhost:8000/api/cities?expand=country or setting extensions_expand = {'country'} on the view (my preferred way), i get a validation error "country": ["This field is required." ].

So using extensions_expand={'country'} results in an error on POST (and also PUT i think). I can bypass this error by using get_extensions_mixin_context on the view

 def get_extensions_mixin_context(self):
        context = super(CityViewSet, self).get_extensions_mixin_context()
        if self.request.method in ['POST', 'PUT']:
            context['expand'] = set()
        return context

This works at least, but still doesn't produce the desired result of having country expanded in the post response.

I also have a repo ready for reproduction: https://github.com/BerniWittmann/drf_serializer_ext
Just try to post something to localhost:8000/api/cities. The desired response would be:

{
        "url": "http://localhost:8000/api/cities/1/",
        "name": "Berlin",
        "id": 1,
        "country": {
            "url": "http://localhost:8000/api/countries/1/",
            "name": "Germany",
            "id": 1,
            "code": "DE"
        },
        "country_id": 1
}

If anything is unclear, let me know :)

[evenicoulddoit]

Hi Ben - I see, thanks for this. I can think of a couple work arounds for your situation, (e.g. recreate the serializer within the view), but I think a more involved fix isn't that trivial. Welcome any pull requests if you manage to look into it (you'd need to modify the serializers module)

[evenicoulddoit]

Hi @BerniWittmann - I realise this is over 2 years old, so apologies, and no worries if you've forgotten altogether, but I had a question.

Am I right to assume that you wanted to post the ID only of the country, but to receive in the response, the fully serialized country?

[BerniWittmann]

Hey @evenicoulddoit, no worries :) I have forgotten about it either.

I guess that this was true indeed.

[nebiyuelias1]

I'm still struggling with this issue today.

[evenicoulddoit]

@nebiyuelias1 can you tell me more?

[nebiyuelias1]

I am basically trying to do the same exact thing as @BerniWittmann.

[nebiyuelias1]

Adding the extensions_expand field to a view somehow makes a field you wanted to expand required somehow.