Extension system

Ariadne implements simple extension system that allows developers to inject custom python logic into the query execution process.

At the moment extension system is only available for ASGI servers. Subscriptions are not supported.

Enabling extensions

To enable extensions, initialize GraphQL app with extensions parameter. This parameter accepts list of extensions:

from ariadne.asgi import GraphQL

from .schema import schema
from .extensions import MyExtension


app = GraphQL(
    schema,
    extensions=[MyExtension]
)

Alternatively, if your extension depends on request or should be enabled conditionally, you can provide callable that will return extensions that should be used:

from ariadne.asgi import GraphQL

from .schema import schema
from .extensions import MyExtension


def get_extensions(request, context):
    if request.headers.get("x-enable-my-extension"):
        return [MyExtension]
    return None


app = GraphQL(
    schema,
    extensions=get_extensions
)

Custom extension example

Let's create simple extension that measures query execution time, and appends this time to query's result.

All extensions should extend special base class named Extension, importable from ariadne.types:

from ariadne.types import Extension


class QueryExecutionTimeExtension(Extension):
    ...

Our extension will measure the query execution time. This means we need to measure the time of two events, request start and finish:

import time

from ariadne.types import Extension


class QueryExecutionTimeExtension(Extension):
    def __init__(self):
        self.start_timestamp = None
        self.end_timestamp = None

    def request_started(self, context):
        self.start_timestamp = time.perf_counter_ns()

    def request_finished(self, context, error=None):
        self.end_timestamp = time.perf_counter_ns()

See Extension reference for the list of available events.

Lastly, extension has to define the format method that will be called by the extension system to obtain data that should be included in GraphQL result:

import time

from ariadne.types import Extension


class QueryExecutionTimeExtension(Extension):
    def __init__(self):
        self.start_timestamp = None
        self.end_timestamp = None

    def request_started(self, context):
        self.start_timestamp = time.perf_counter_ns()

    def request_finished(self, context, error=None):
        self.end_timestamp = time.perf_counter_ns()

    def format(self):
        if self.start_timestamp and self.end_timestamp:
            return {
                "execution": self.start_timestamp - self.end_timestamp
            }