Pagination

Django provides a few classes that help you manage paginated data – that is, data that’s split across several pages, with “Previous/Next” links.

— Django documentation

REST framework includes a PaginationSerializer class that makes it easy to return paginated data in a way that can then be rendered to arbitrary media types.

Paginating basic data

Let's start by taking a look at an example from the Django documentation.

from django.core.paginator import Paginator
objects = ['john', 'paul', 'george', 'ringo']
paginator = Paginator(objects, 2)
page = paginator.page(1)
page.object_list
# ['john', 'paul']

At this point we've got a page object. If we wanted to return this page object as a JSON response, we'd need to provide the client with context such as next and previous links, so that it would be able to page through the remaining results.

from rest_framework.pagination import PaginationSerializer
serializer = PaginationSerializer(instance=page)
serializer.data
# {'count': 4, 'next': '?page=2', 'previous': None, 'results': [u'john', u'paul']}

The context argument of the PaginationSerializer class may optionally include the request. If the request is included in the context then the next and previous links returned by the serializer will use absolute URLs instead of relative URLs.

request = RequestFactory().get('/foobar')
serializer = PaginationSerializer(instance=page, context={'request': request})
serializer.data
# {'count': 4, 'next': 'http://testserver/foobar?page=2', 'previous': None, 'results': [u'john', u'paul']}

We could now return that data in a Response object, and it would be rendered into the correct media type.

Paginating QuerySets

Our first example worked because we were using primative objects. If we wanted to paginate a queryset or other complex data, we'd need to specify a serializer to use to serialize the result set itself with.

We can do this using the object_serializer_class attribute on the inner Meta class of the pagination serializer. For example.

class UserSerializer(serializers.ModelSerializer):
    """
    Serializes user querysets.
    """
    class Meta:
        model = User
        fields = ('username', 'email')

class PaginatedUserSerializer(pagination.PaginationSerializer):
    """
    Serializes page objects of user querysets.
    """
    class Meta:
        object_serializer_class = UserSerializer

We could now use our pagination serializer in a view like this.

@api_view('GET')
def user_list(request):
    queryset = User.objects.all()
    paginator = Paginator(queryset, 20)

    page = request.QUERY_PARAMS.get('page')
    try:
        users = paginator.page(page)
    except PageNotAnInteger:
        # If page is not an integer, deliver first page.
        users = paginator.page(1)
    except EmptyPage:
        # If page is out of range (e.g. 9999), deliver last page of results.
        users = paginator.page(paginator.num_pages)

    serializer_context = {'request': request}
    serializer = PaginatedUserSerializer(instance=users,
                                         context=serializer_context)
    return Response(serializer.data)

Pagination in the generic views

The generic class based views ListAPIView and ListCreateAPIView provide pagination of the returned querysets by default. You can customise this behaviour by altering the pagination style, by modifying the default number of results, or by turning pagination off completely.

The default pagination style may be set globally, using the PAGINATION_SERIALIZER and PAGINATE_BY settings. For example.

REST_FRAMEWORK = {
    'PAGINATION_SERIALIZER': (
        'example_app.pagination.CustomPaginationSerializer',
    ),
    'PAGINATE_BY': 10
}

You can also set the pagination style on a per-view basis, using the ListAPIView generic class-based view.

class PaginatedListView(ListAPIView):
    model = ExampleModel
    pagination_serializer_class = CustomPaginationSerializer
    paginate_by = 10

For more complex requirements such as serialization that differs depending on the requested media type you can override the .get_paginate_by() and .get_pagination_serializer_class() methods.

Custom pagination serializers

To create a custom pagination serializer class you should override pagination.BasePaginationSerializer and set the fields that you want the serializer to return.

You can also override the name used for the object list field, by setting the results_field attribute, which defaults to 'results'.

Example

For example, to nest a pair of links labelled 'prev' and 'next', and set the name for the results field to 'objects', you might use something like this.

class LinksSerializer(serializers.Serializer):
    next = pagination.NextURLField(source='*')
    prev = pagination.PreviousURLField(source='*')

class CustomPaginationSerializer(pagination.BasePaginationSerializer):
    links = LinksSerializer(source='*')  # Takes the page object as the source
    total_results = serializers.Field(source='paginator.count')

    results_field = 'objects'

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