Extensions

Extensions allow you to add custom functionality to your graph.

Extensions are classes that inherit from hiku.extensions.Extension.

Each extension has a set of methods that are called at different stages of graph processing.

Here are all the methods that can be implemented:

• on_graph() - when endpoint is created and transformations applied to graph

• on_dispatch() - when query is dispatched to the endpoint

• on_parse() - when query string is parsed into ast

• on_operation() - when query ast parsed into query Node

• on_validate() - when query is validated

• on_execute() - when query is executed by engine

Built-in extensions

• QueryParseCache - cache parsed graphql queries ast.

• QueryTransformCache - cache transformed graphql ast into query Node.

• QueryValidationCache - cache query validation.

• QueryDepthValidator - validate query depth

• PrometheusMetrics - wrapper around GraphMetrics visitor

• PrometheusMetricsAsync - wrapper around AsyncGraphMetrics visitor

• CustomContext - allows to pass custom context to the query execution

Writing extension

from typing import Iterator

from hiku.extensions.base_extension import Extension
from hiku.context import ExecutionContext

class TimeItExtension(Extension):
    def on_execute(self, execution_context: ExecutionContext) -> Iterator[None]:
        start = time.perf_counter()
        yield
        print('Query execution took {:.3f} seconds'.format(time.perf_counter() - start))

endpoint = GraphqlEndpoint(engine, graph, extensions=[TimeItExtension()])