0.24

Customizing Query Stack

Ariadne lets to developers to replace both parsing and validating steps of the query execution stack with custom logic.

Query parser

Default GraphQL query parser used by Ariadne is the parse function from the graphql-core package:

from graphql import parse

document = parse("{ query string }")

This function takes the str with the GraphQL query, and parsers it into a DocumentNode instance containing the GraphQL AST representation of the query.

Ariadne's GraphQL() ASGI and WSGI apps together with graphql(), graphql_sync() and subscribe() functions accept the query_parser named argument that lets server developers to provide a custom function to use for parsing queries.

If custom parser is set, this parser is called with two arguments:

  • context: ContextValue
  • data: dict[str, Any]: a dict with current operation's payload (query, operationName and variables).

Here's an example custom parser function that only parses the query string from query's payload:

from ariadne.types import ContextValue
from graphql import DocumentNode, parse


def caching_query_parser(context: ContextValue, data: dict[str, Any]) -> DocumentNode:
    return parse(data["query"])

Query validation

Ariadne's GraphQL query validation uses the validate function from the graphql-core package to validate a query against a schema and a set of rules. This function can be swapped out in GraphQL servers using the query_validator option.

Custom validator should have a following signature:

from typing import Collection, Type

from graphql import (
    GraphQLSchema,
    DocumentNode,
    ASTValidationRule,
    TypeInfo,
)


def custom_query_validator(
    schema: GraphQLSchema,
    document_ast: DocumentNode,
    rules: Collection[Type[ASTValidationRule]] | None = None,
    max_errors: int | None = None,
    type_info: TypeInfo | None = None,
) -> list[GraphQLError]:
    return []  # List of `GraphQLError`s with problems with the query

Examples

Caching parsed queries

Following example shows a custom query parser that caches a number of GraphQL queries using the LRU approach. This parser will raise memory usage of the GraphQL server, but will improve query response times:

from functools import lru_cache

from ariadne.types import ContextValue
from graphql import DocumentNode, parse


parse_cached = lru_cache(maxsize=64)(parse)


def caching_query_parser(context: ContextValue, data: dict[str, Any]) -> DocumentNode:
    # Custom parser function is called with the context and entire query's payload.
    return parse_cached(data["query"])


# Pass the 'caching_query_parser' to the 'query_parser' option of the 'GraphQL'
graphql = GraphQL(schema, query_parser=caching_query_parser)

Combined parse and validation cache

The below code combines custom parser and validator functions to add caching to both query parsing and validation parts of the Query Stack:

from collections.abc import Collection
from functools import lru_cache
from typing import Any

from ariadne import make_executable_schema
from ariadne.asgi import GraphQL
from ariadne.graphql import validate_query
from ariadne.types import ContextValue
from graphql import ASTValidationRule, DocumentNode, GraphQLError, GraphQLSchema, TypeInfo, parse


parse_cached = lru_cache(maxsize=64)(parse)


def caching_query_parser(context: ContextValue, data: dict[str, Any]) -> DocumentNode:
    # Custom parser function is called with the context and entire query's payload.
    return parse_cached(data["query"])


validate_query_cached = lru_cache(maxsize=64)(validate_query)


def caching_query_validator(
    schema: GraphQLSchema,
    document_ast: DocumentNode,
    rules: Collection[type[ASTValidationRule]] | None = None,
    max_errors: int | None = None,
    type_info: TypeInfo | None = None,
) -> list[GraphQLError]:
    return validate_query_cached(
        schema=schema,
        document_ast=document_ast,
    )


# Add type definitions, resolvers, etc...
schema = make_executable_schema("...")

# Using our custom functions for parsing & validation
graphql = GraphQL(
    schema,
    query_parser=caching_query_parser,
    query_validator=caching_query_validator,
)
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