django-infinite-scroll-pagination 0.1

infinite-scroll-pagination is a Django app that implements the *seek method* for scalable pagination..

infinite-scroll-pagination is a Django app that implements the seek method (AKA Keyset Paging) for scalable pagination.

How it works

Keyset driven paging relies on remembering the top and bottom keys of the last displayed page, and requesting the next or previous set of rows, based on the top/last keyset

This approach has two main advantages over the OFFSET/LIMIT approach:

• is correct: unlike the offset/limit based approach it correctly handles new entries and deleted entries. Last row of Page 4 does not show up as first row of Page 5 just because row 23 on Page 2 was deleted in the meantime. Nor do rows mysteriously vanish between pages. These anomalies are common with the offset/limit based approach, but the keyset based solution does a much better job at avoiding them.

• is fast: all operations can be solved with a fast row positioning followed by a range scan in the desired direction

For a full explanation go to the seek method

Requirements

infinite-scroll-pagination requires the following software to be installed:

• Python 2.7

• Django +1.4 (tested locally on 1.6)

Configuration

1. None :smile:

Usage

Paging by date or any other field:

# views.py

from infinite_scroll_pagination.paginator import SeekPaginator


def pagination_ajax(request, pk=None):
    if not request.is_ajax():
        return Http404()

    if pk is not None:
        # I'm doing an extra query because datetime serialization/deserialization is hard
        date = get_object_or_404(Article, pk=pk).date
    else:
        # is requesting the first page
        date = None

    articles = Article.objects.all()
    paginator = SeekPaginator(articles, per_page=20, lookup_field="date")
    page = paginator.page(value=date, pk=pk)

    articles_list = [{"title": a.title, } for a in page]
    data = {'articles': articles_list,
            'has_next': page.has_next(),
            'pk': page[-1].pk}

    return HttpResponse(json.dumps(data), content_type="application/json")

Paging by pk or id (special case):

# views.py

def pagination_ajax(request, pk=None):
    #...

    page = paginator.page(value=pk, pk=pk)

    #...

Showing how many objects (or pages) are left:

Note: For true infinite scroll, this is not recommended. Since it does a count() query.

It would be better if you increase an IntegerField every time a record is saved and do some javascript magic to know how many objects are left.

#...

page_first = paginator.page()

data = {'objects_left_count': page_first.objects_left,
        'pages_left_count': page_first.pages_left,
        #...}

Limitations

• I decided not to implement the get previous page because there is no way to know if the previous page even exists anymore, rows may have been removed. Although, it’d work for dynamic content that inserts rows (but does not delete them). If you have some thoughts about how this can be solved, you may open an issue.

• Order is DESC (from newest to latest). You may submit a pull request for ASC order support.

Contributing

Feel free to check out the source code and submit pull requests.

You may also report any bug or propose new features in the issues tracker

Copyright / License

Copyright 2014 Esteban Castro Borsani.

Licensed under the MIT License.

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an “AS IS” BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.