Strawberry Generic Connections (Python 3.10 syntax)

01_connections.py

from typing import Generic, TypeVar

import strawberry

ConnectionNode = TypeVar("ConnectionNode")


@strawberry.type
class Edge(Generic[ConnectionNode]):
    node: ConnectionNode
    cursor: str


@strawberry.type
class PageInfo:
    has_next_page: bool
    has_previous_page: bool
    start_cursor: str | None
    end_cursor: str | None


EdgeType = TypeVar(name="EdgeType", bound=Edge)


@strawberry.type
class Connection(Generic[EdgeType]):
    edges: list[EdgeType]
    page_info: PageInfo

02_usage.py

from .connections import Connection, ConnectionNode, Edge, PageInfo

from ..books import Book, ALL_BOOKS
from ..events import Event, ALL_EVENTS


@strawberry.field
def all_books(
    first: int | None = None,
    last: int | None = None,
    before: str | None = None,
    after: str | None = None,
) -> Connection[Edge[Book]]:   
    return Connection(
        edges=[Edge(node=x, cursor='some-derived-cursor') for x in ALL_BOOKS],
        page_info=PageInfo(
            has_next_page=False,
            has_previous_page=False,
            start_cursor=None,
            end_cursor=None,
        ),
    )
  
@strawberry.type
class DistanceEdge(Edge[ConnectionNode]):
    distance_km: float
  
  
@strawberry.field
def nearby_events(
    first: int | None = None,
    last: int | None = None,
    before: str | None = None,
    after: str | None = None,
    near: LatLngInput,
) -> Connection[DistanceEdge[Event]]:
    return Connection(
        edges=[DistanceEdge(node=x, cursor='some-derived-cursor', distance=50.0) for x in ALL_EVENTS],
        page_info=PageInfo(
            has_next_page=False,
            has_previous_page=False,
            start_cursor=None,
            end_cursor=None,
        ),
    )

03_schema.graphql

# Partial output of schema

type PageInfo {
  hasNextPage: Boolean!
  hasPreviousPage: Boolean!
  startCursor: String
  endCursor: String
}

type BookEdge {
  node: Book!
  cursor: String!
}

type BookEdgeConnection {
  edges: [BookEdge!]!
  pageInfo: PageInfo!
}

type EventDistanceEdge {
  node: Event!
  cursor: String!
  distanceKm: Float!
}

type EventDistanceEdgeConnection {
  edges: [EventDistanceEdge!]!
  pageInfo: PageInfo!
}

type Query {
  allBooks(first: Int, last: Int, before: String, after: String): BookEdgeConnection!
  nearbyEvents(first: Int, last: Int, before: String, after: String, near: LatLngInput!): EventDistanceEdgeConnection!
}