dynamically modifying fields in DRF3

[张留成]

Hi All:

I'm a new one to the  DRF3, i want to know how to dynamically modifying fields.

i follow the link： http://www.django-rest-framework.org/api-guide/serializers/#dynamically-modifying-fields . 

 that's mean i can't use the ModelViewSet ? 

the fields is from the request params ,is there any way get the request params like this (red color):

class DynamicFieldsModelSerializer(serializers.ModelSerializer):

    """

    A ModelSerializer that takes an additional `fields` argument that

    controls which fields should be displayed.

    """

    def __init__(self, *args, **kwargs):

        # Instantiate the superclass normally

        super(DynamicFieldsModelSerializer, self).__init__(*args, **kwargs)

        fields = self.request.get('fields')

        no_fields = self.request.get('nofields')

        if fields is not None:

            # Drop any fields that are not specified in the `fields` argument.

            allowed = set(fields[1:-1].split(','))

            existing = set(self.fields.keys())

            for field_name in existing - allowed:

                self.fields.pop(field_name)

        if no_fields is not None:

            for field_name in set(no_fields[1:-1].split(',')):

                self.fields.pop(field_name)

[Zoltan Szalai]

you should normally be able to access the request object in the serializer via the context attr (if the serializer got instantiated from a GenericAPIView subclass):
request = self.context.get('request')
and then:
request.query_params.get('fields')
request.query_params.get('nofields')
etc.

but if you happen to use the default pagination then it's not working. at least in 3.0.2. which is a bug I guess, but I don't have time to dig deeper right now.

On 2014.12.25. 3:56, 张留成 wrote:

Hi All:

I'm a new one to the  DRF3, i want to know how to dynamically modifying fields.

i follow the link： http://www.django-rest-framework.org/api-guide/serializers /#dynamically-modifying-fields . 

 that's mean i can't use the ModelViewSet ? 

the fields is from the request params ,is there any way get the request params like this (red color):

class DynamicFieldsModelSerializer(serializers.ModelSerializer):

    """

    A ModelSerializer that takes an additional `fields` argument that

    controls which fields should be displayed.

    """

    def __init__(self, *args, **kwargs):

        # Instantiate the superclass normally

        super(DynamicFieldsModelSerializer, self).__init__(*args, **kwargs)

        fields = self.request.get('fields')

        no_fields = self.request.get('nofields')

        if fields is not None:

            # Drop any fields that are not specified in the `fields` argument.

            allowed = set(fields[1:-1].split(','))

            existing = set(self.fields.keys())

            for field_name in existing - allowed:

                self.fields.pop(field_name)

        if no_fields is not None:

            for field_name in set(no_fields[1:-1].split(',')):

                self.fields.pop(field_name)

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[Tom Christie]

> but if you happen to use the default pagination then it's not working. at least in 3.0.2. which is a bug I guess

I'm not sure what's being referred to there - you might consider raising an issue if you think there's a problem.

[Zoltan Szalai]

hi Tom,

https://github.com/tomchristie/django-rest-framework/issues/2355
hope this helps to reproduce it.

bests
Zoli

[andyz]

Thanks for u reply .. i will try as you say 

在 2014年12月25日，下午10:28，Zoltan Szalai <defau...@gmail.com> 写道：

pagination

[andyz]

Hi Zoli:

I'm try as you said . it only works at api which without pagination. 

Do you have found the way work with paination? Could you help to offer a simple ? 

thanks a lot  

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[andyz]

Hi：

The code seems like that .don't init with the args at BasePaginationSerializer. 

It works fine when i change the code as bellow.

​

i have created a pull request for this 

[Renzo Canepa]

Hi Zolta,

Did you accomplish what you wanted?. I think I am facing the same situation. I need to dynamically set the fields using data from request parameters. This is my code:

class DynamicFieldsModelSerializer(serializers.ModelSerializer):
    """
    A ModelSerializer that takes an additional `fields` argument that
    controls which fields should be displayed.
    """


    def __init__(self, *args, **kwargs):

        super(DynamicFieldsModelSerializer, self).__init__(*args, **kwargs)

        request = self.context.get('request')

        print request
        fields = request.query_params.get('fields')

        if fields is not None:
            # Drop any fields that are not specified in the `fields` argument.

            allowed = set(fields)

            existing = set(self.fields.keys())
            for field_name in existing - allowed:
                self.fields.pop(field_name)

The print request statement is printing the next lines (for every time I make a request to the view):

None

None

<rest_framework.request.Request object at 0x7f3ac1c96d50>

<rest_framework.request.Request object at 0x7f3ac1635190>

<rest_framework.request.Request object at 0x7f3ac1635fd0>

And I am getting this error:

File "/home/rcanepa/Development/simpleclerk/simpleclerk/utils.py", line 22, in __init__

    fields = request.query_params.get('fields')

AttributeError: 'NoneType' object has no attribute 'query_params'

How did you solve it?

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[Renzo Canepa]

I found a solution for my need. I will leave it here in case that anyone need to solve the same problem.

You can pass the fields in the URL in this way: http://localhost:8000/api/persons?fields=id,first_name,organization

class DynamicFieldsModelSerializer(serializers.ModelSerializer):
    """

    A ModelSerializer that takes an additional `fields` argument that

    controls which fields should be displayed. The argument comes
    from the request object.

    """


    def __init__(self, *args, **kwargs):
        super(DynamicFieldsModelSerializer, self).__init__(*args, **kwargs)

        request = self.context.get('request', None)
        if request and request.method == 'GET':
            fields = request.query_params.get('fields', None)

            if fields is not None:

                allowed = set(fields.split(','))

                existing = set(self.fields.keys())
                for field_name in existing - allowed:
                    self.fields.pop(field_name)

[andyz]

Hi Renzo:

Seems like that , the solution you privoid is not work! the request is still None!

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[Renzo Canepa]

Hi,

Are you sure?. This line should do the trick:

if request and request.method == 'GET':

I successfully used it on one of my API's REST point.

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[andyz]

hmm... 

for example : 

GET /test/

{

    "id":1,

    "name":"test"

}

GET /test/?fields=id

{

    "id":1

}

work like this ?

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[Renzo Canepa]

Yeah, that is what I was looking for.

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[Tom Christie]

> if you happen to use the default pagination then it's not working. at least in 3.0.2. which is a bug I guess

Now resolved. See https://github.com/tomchristie/django-rest-framework/issues/2355 for more details.