Refresh from DB when updating nested object

[pcarn]

When I make a PUT or PATCH request on an object that includes changes to a nested model, the response does not include the changes.
But when I do a GET on the object after that, it shows the changes. It is making the change, but not returning it in the response.

I've confirmed that adding a refresh_from_db() in the update serializer fixes this. It responds with the changes I made, and behaves like I'd expect.

Example:
Models:

class Question(BaseModel):
    text = models.CharField(max_length=50)

class Option(BaseModel):
    question = models.ForeignKey(
        "Question", related_name="options", on_delete=models.CASCADE,
    )
    text = models.CharField(max_length=50)

Serializers:

class OptionSerializer(DynamicFieldsModelSerializer):
    class Meta:
        model = models.Option
        fields = (
            "id",
            "text",
        )

class QuestionSerializer(WritableNestedModelSerializer):
    options = OptionSerializer(many=True)

    class Meta:
        model = models.Question
        fields = (
            "id",
            "text",
            "options",
        )

Before these changes:

GET /api/events/questions/cc464c6e-79f8-496d-9aad-d98a7fff11a5/
Response:
{
    "id": "cc464c6e-79f8-496d-9aad-d98a7fff11a5",
    "text": "what is the best cheese?",
    "options": [
        {
            "id": "8cd27b47-129d-4093-8132-0bbcfc17a45a",
            "text": "cheddar"
        },
        {
            "id": "8d53d35c-9694-40d2-9e7c-e1ad83f99bb5",
            "text": "gouda"
        }
    ]
}

PATCH /api/events/questions/cc464c6e-79f8-496d-9aad-d98a7fff11a5/
Body:
{
    "options": [
        {
            "id": "8cd27b47-129d-4093-8132-0bbcfc17a45a",
            "text": "cheddar"
        },
        {
            "id": "8d53d35c-9694-40d2-9e7c-e1ad83f99bb5",
            "text": "gouda"
        },
        {
            "text": "swiss"
        }
    ]
}
Response:
{
    "id": "cc464c6e-79f8-496d-9aad-d98a7fff11a5",
    "text": "what is the best cheese?",
    "options": [
        {
            "id": "8cd27b47-129d-4093-8132-0bbcfc17a45a",
            "text": "cheddar"
        },
        {
            "id": "8d53d35c-9694-40d2-9e7c-e1ad83f99bb5",
            "text": "gouda"
        }
    ]
}

GET /api/events/questions/cc464c6e-79f8-496d-9aad-d98a7fff11a5/
Response:
{
    "id": "cc464c6e-79f8-496d-9aad-d98a7fff11a5",
    "text": "what is the best cheese?",
    "options": [
        {
            "id": "8cd27b47-129d-4093-8132-0bbcfc17a45a",
            "text": "cheddar"
        },
        {
            "id": "8d53d35c-9694-40d2-9e7c-e1ad83f99bb5",
            "text": "gouda"
        },
        {
            "id": "6b33788e-298d-4408-b6ea-dd7dcd1c8232",
            "text": "swiss"
        }
    ]
}

After these changes:

GET /api/events/questions/cc464c6e-79f8-496d-9aad-d98a7fff11a5/
Response:
{
    "id": "cc464c6e-79f8-496d-9aad-d98a7fff11a5",
    "text": "what is the best cheese?",
    "options": [
        {
            "id": "8cd27b47-129d-4093-8132-0bbcfc17a45a",
            "text": "cheddar"
        },
        {
            "id": "8d53d35c-9694-40d2-9e7c-e1ad83f99bb5",
            "text": "gouda"
        }
    ]
}

PATCH /api/events/questions/cc464c6e-79f8-496d-9aad-d98a7fff11a5/
Body:
{
    "options": [
        {
            "id": "8cd27b47-129d-4093-8132-0bbcfc17a45a",
            "text": "cheddar"
        },
        {
            "id": "8d53d35c-9694-40d2-9e7c-e1ad83f99bb5",
            "text": "gouda"
        },
        {
            "text": "swiss"
        }
    ]
}
Response:
{
    "id": "cc464c6e-79f8-496d-9aad-d98a7fff11a5",
    "text": "what is the best cheese?",
    "options": [
        {
            "id": "8cd27b47-129d-4093-8132-0bbcfc17a45a",
            "text": "cheddar"
        },
        {
            "id": "8d53d35c-9694-40d2-9e7c-e1ad83f99bb5",
            "text": "gouda"
        },
        {
            "id": "6b33788e-298d-4408-b6ea-dd7dcd1c8232",
            "text": "swiss"
        }
    ]
}

GET /api/events/questions/cc464c6e-79f8-496d-9aad-d98a7fff11a5/
Response:
{
    "id": "cc464c6e-79f8-496d-9aad-d98a7fff11a5",
    "text": "what is the best cheese?",
    "options": [
        {
            "id": "8cd27b47-129d-4093-8132-0bbcfc17a45a",
            "text": "cheddar"
        },
        {
            "id": "8d53d35c-9694-40d2-9e7c-e1ad83f99bb5",
            "text": "gouda"
        },
        {
            "id": "6b33788e-298d-4408-b6ea-dd7dcd1c8232",
            "text": "swiss"
        }
    ]
}

[codecov-io]

Codecov Report

Merging #122 into master will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #122   +/-   ##
=======================================
  Coverage   98.13%   98.13%           
=======================================
  Files           3        3           
  Lines         214      215    +1     
=======================================
+ Hits          210      211    +1     
  Misses          4        4           

Impacted Files	Coverage Δ
drf_writable_nested/mixins.py	98.02% <100.00%> (+<0.01%)	⬆️

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[pcarn]

I can use a workaround by adding this to QuestionSerializer:

    def update(self, instance, validated_data):
        updated_instance = super().update(instance, validated_data)
        updated_instance.refresh_from_db()
        return updated_instance

But this seems like something that should be default behavior, and it would be nice to not need a workaround.

[ruscoder]

Hello @pcarn! Thanks for your contribution. Could you please add tests covering your case (tests that fail without this PR)?

[ruscoder]

It seems like a good improvement, I'm ready to merge it to the master.

[pcarn]

@ruscoder Thanks! Added tests

[pcarn]

@ruscoder Can this be merged so I can start using it?

[ruscoder]

@pcarn Thanks! I've just published version 0.6.2 which includes your fix.