Apollo Federation Support

[patrick91]

I was thinking of adding support for Apollo Federation, in order to make this happen the following TODOs need to be tackled:

• Allow support for custom directives Custom directives #109
  not really true, but having a pythonic way of defining directives will help
• Output types in schema even if they are not used by a query
  Right now we only output fields that are used (directly and indirectly) in a query. Federated schemas might not define a query at all, so we need to output types anyway.
• Add support for custom scalars Add support for scalar types #3

Federation specification

scalar _Any
scalar _FieldSet

# a union of all types that use the @key directive
union _Entity

type _Service {
  sdl: String
}

extend type Query {
  _entities(representations: [_Any!]!): [_Entity]!
  _service: _Service!
}

directive @external on FIELD_DEFINITION
directive @requires(fields: _FieldSet!) on FIELD_DEFINITION
directive @provides(fields: _FieldSet!) on FIELD_DEFINITION
directive @key(fields: _FieldSet!) on OBJECT | INTERFACE

directive @extends on OBJECT | INTERFACE

Federation spec: https://www.apollographql.com/docs/apollo-server/federation/federation-spec/

Python API

Initial Ideas

type Review {
  body: String
  author: User @provides(fields: "username")
  product: Product
}

extend type User @key(fields: "id") {
  id: ID! @external
  reviews: [Review]
}

extend type Product @key(fields: "upc") {
  upc: String! @external
  reviews: [Review]
}

@strawberry.type
class Review:
  body: str
  author: User = strawberry.field(directives=[provides(fields="username")])
  product: Product


@strawberry.type(extend=True, directives=[key(fields="id")])
class User:
  id: ID = strawberry.field(directives=[external()])
  reviews: typing.list[Review]


@strawberry.type(extend=True, directives=[key(fields="upc")])
class Product:
  upc: str = strawberry.field(directives=[external()])
  reviews: typing.list[Review]

[patrick91]

Another example, a bit more abstracted:

import strawberry
import typing


@strawberry.federation.extend(keys=["upc"])
class Product:
    upc: str = strawberry.federation.external_field()
    reviews: typing.list["Review"]


@strawberry.federation.extend(keys=["id"])
class User:
    id: strawberry.ID = strawberry.federation.external_field()
    reviews: typing.list["Review"]


@strawberry.type
class Review:
    body: str
    author: User = strawberry.federation.provider_field("username")
    product: Product


schema = strawberry.federation.FederatedSchema()

[ethe]

I think author: User = strawberry.field(directives=[provides(fields="username")]) does not make sense in Python semantics. strawberry.field(directives=[provides(fields="username")]) is not a default value to Review.author as User type. It can not pass the type checking in mypy I think.

[Ambro17]

I would like to help in any task available to give support to Apollo federation to strawberry. I personally prefer the first alternative as it is more easily translatable to the SDL

[patrick91]

Hey @Ambro17! I did an initial PR here: #259

Would you like to give me a review? Code isn't great, but it worked with a simple test-scenario 😊

[Ambro17]

Hello Patrick, the other day I looked over the PR and made some comments

[patrick91]

@Ambro17 don't see any comments 🤔 I saw your issue, but no comments on the PR

[Ambro17]

My bad, I thought that merely writing the comments was enough, but apparently github requires to end your review with a comment/request changes/approve. Now you should be able to see my comments

[patrick91]

My bad, I thought that merely writing the comments was enough, but apparently github requires to end your review with a comment/request changes/approve. Now you should be able to see my comments

No worries! It happened to me as well a few times ^^ Thanks for the comments. By the way, I put federation on hold at the moment as I was trying to understand how to make a pagination API. By the way I was thinking of using discord and maybe livestream/pair with other people since we are all at home nowadays :D Here’s the link: https://discord.gg/ZkRTEJQ if you want to join ^^

[japrogramer]

@patrick91 Relay does pagination fairly well. I made a pagination that extends relay

connection_type(
edges=edges,
page_info=page
)

where connection_type returns an object type with fields edges and page_info,
the connection takes a page and per_page argument by default.

edges is an array of types and page_info is a type that describes the results

class PaginatorInfo(graphene.ObjectType):
    count = Int(
        name='Count',
        description='The total number of objects, across all pages.'
    )

    current_page = Int(
        name='CurrentPage',
        description='The current page number.'
    )

    num_pages = Int(
        name='NumPages',
        description='The total number of pages.'
    )

    page_range = List(
        Int,
        name='PageRange',
        description='A 1-based range iterator of page numbers, e.g. yielding [1, 2, 3, 4].'
    )

    has_next = Boolean(
        description='Returns True if there\'s a next page.')

    has_previous = Boolean(
        description='Returns True if there\'s a previous page.')

    has_other_pages = Boolean(
        description='Returns True if there\'s a next or previous page.')

    next_page_number = Int(
        description='Returns the next page number. Raises InvalidPage if next page'
                    'doesn\'t exist.')

    previous_page_number = Int(
        description='Returns the previous page number. Raises InvalidPage if'
                    'previous page doesn\'t exist.')

    start_index = Int(
        description='Returns the 1-based index of the first object on the page,'
                    'relative to all of the objects in the paginator\'s list. For example,'
                    ' when paginating a list of 5 objects with 2 objects per page, the'
                    'second page\'s start_index() would return 3.')

    end_index = Int(
        description='Returns the 1-based index of the last object on the page,'
                    'relative to all of the objects in the paginator\'s list. For'
                    'example, when paginating a list of 5 objects with 2 objects'
                    'per page, the second page\'s end_index() would return 4.')

[patrick91]

@japrogramer did mean to write a comment here: #175?

[japrogramer]

@patrick91 I was responding to your comment in this issue, was not aware of #175

[patrick91]

@japrogramer my bad, I forgot what I wrote :D

[patrick91]

This is done, we'll add documentation and examples soon, I'll close this now 😊

[Speedy1991]

Hey @patrick91!

Any chance to get some docs on federation in the next time?
I would write some docs myself and give you a PR but I'm not sure, that I fully understand federation yet.
A minimal working example would be great with some introducing words to the decorators.

[patrick91]

Hi @Speedy1991 I have some docs here: #440

I wanted to make a full example[1], but didn't manage to make time, would you like to make one? We can put it in our strawberry-graphql/examples repo 😊

Feel free to join our discord and ask questions there too 😊 https://strawberry.rocks/discord

[1] https://github.com/patrick91/strawberry-federation-demo

[Sheikhharis50]

Hi @patrick91,

can you help me out with the N+1 problem in the federation? I have used the same approach given in the documentation of strawberry and it was extremely helpful, but I have observed that it's causing an N+1 problem, is there any example in which I can use Dataloader to resolve this issue.

I tried using Dataloader but it seems when I try to use in resolve_reference method and change it to async it doesn't work at all.

Followings are my findings, they may help you:
RuntimeWarning: coroutine 'ExecutionContext.execute_fields..get_results' was never awaited
RuntimeWarning: coroutine 'ExecutionContext.execute_field..await_completed' was never awaited
RuntimeWarning: coroutine 'ExecutionContext.complete_list_value..get_completed_results' was never awaited
RuntimeWarning: coroutine 'ExecutionContext.complete_list_value..await_completed' was never awaited
RuntimeWarning: coroutine 'ProductType.resolve_reference' was never awaited

The last one is my method and it says it was never awaited and I am not calling it, I think it calls in strawberry.

Thanks