Polling (Auto-refresh)

Charts can auto-refresh by fetching new data via HTTP at regular intervals. No WebSocket, no MQTT — just plain fetch().

How It Works

1. Chart renders with initial data from the Django view
2. JavaScript fetches the poll_url every poll_interval seconds
3. Chart re-renders with new data (animated transition)

Quick Example

# views.py
from d3_bridge import BarChart
from d3_bridge.views import ChartDataView

def dashboard(request):
    chart = BarChart(
        data=Product.objects.values("name", "stock"),
        x="name", y="stock",
        title="Current Stock",
        poll_url="/api/chart/stock/",
        poll_interval=15,  # refresh every 15 seconds
    )
    return render(request, "dashboard.html", {"chart": chart})

# urls.py
from d3_bridge.views import ChartDataView

urlpatterns = [
    path("api/chart/stock/", ChartDataView.as_view(
        queryset=Product.objects.all(),
        fields=["name", "stock"],
        ordering="-stock",
    )),
]

Replace vs Append Mode

Replace (default)

Each poll replaces all chart data:

chart = BarChart(
    data=data, x="x", y="y",
    poll_url="/api/data/",
    poll_interval=30,
    poll_replace=True,  # default
)

Append

New data is appended to existing data, with a sliding window:

chart = LineChart(
    data=initial_readings,
    x="timestamp", y="value",
    poll_url="/api/latest-reading/",
    poll_interval=5,
    poll_replace=False,   # append mode
    poll_window=100,      # keep last 100 points
)

Custom Headers

chart = BarChart(
    data=data, x="x", y="y",
    poll_url="/api/data/",
    poll_interval=30,
    poll_headers={"Authorization": "Bearer my-token"},
)

ChartDataView

A lightweight JSON endpoint included in the package. No Django REST Framework required.

from d3_bridge.views import ChartDataView

urlpatterns = [
    path("api/chart/sales/", ChartDataView.as_view(
        queryset=Sale.objects.all(),
        fields=["date", "amount", "product"],
        ordering="-date",
        limit=100,
    )),
]

Option	Type	Description
queryset	QuerySet	Data source (re-evaluated each request)
fields	list	Fields to include
ordering	str or list	Order by field(s)
limit	int	Max records
geojson	bool	Serialize as GeoJSON

Override get_queryset() or filter_queryset() for dynamic filtering:

class SalesByRegion(ChartDataView):
    queryset = Sale.objects.all()
    fields = ["product", "amount"]

    def filter_queryset(self, qs):
        region = self.request.GET.get("region")
        if region:
            qs = qs.filter(region=region)
        return qs

Smart Behavior

• Pauses when tab is hidden — saves bandwidth (Page Visibility API)
• Exponential backoff — on network errors, waits progressively longer before retrying
• CSRF token — auto-detected from Django's cookie
• Same-origin credentials — included automatically

Parameters

Parameter	Type	Default	Description
poll_url	str	None	URL to fetch data from
poll_interval	int	0	Seconds between fetches (0 = disabled)
poll_replace	bool	True	Replace all data (True) or append (False)
poll_window	int	None	Max data points in append mode
poll_headers	dict	None	Custom HTTP headers