This document discusses lessons learned from building a GraphQL API on top of a Django application. It covers how Django and Graphene can be used to rapidly build APIs by mapping models to GraphQL types. It notes that mutations can be tricky due to a lack of input validation and unified errors. It recommends using abstractions and patterns like CRUD to simplify mutations. It also addresses challenges with subscriptions due to Django's synchronous nature and need for additional libraries for features like authentication and federation.

1. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Real World
Graphene
Lessons learned from building
a GraphQL API on top of a Django app
Marcin Gebala

2. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Hi, I’m Marcin
● Wrocław, Poland
@maarcingebala
● Python developer at Mirumee
● Development lead at Saleor

3. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE

4. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE

5. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE

6. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Saleor GraphQL API
● 50 queries, 200 mutations, 500 types
● JWT authentication & permissions
● Service accounts & webhooks
● Filtering, sorting & search capabilities

7. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
It’s open-source 🎉
github.com/mirumee/saleor
Public demo
pwa.saleor.io

8. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Migration to headless architecture

9. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Migration to headless architecture

10. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
● Most popular GraphQL framework in Python
● Code-first approach
○ building types and operations in Python
○ schema is generated
● Support for popular Python web
frameworks like Django, Flask & Tornado
Graphene

11. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Graphene
4 lessons you won’t learn
from the docs

12. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Lesson 1
Django + Graphene let you
rapidly build APIs

13. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Example user model in Django

14. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Mapping a model to Graphene type

15. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Mapping a model to Graphene type

16. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Mapping a model to Graphene type

17. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Defining queries and resolvers

18. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
GraphQL schema

19. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
● Effective if you’re building GraphQL on top of
existing codebase.
● Control over which fields are mapped
● Declarative and class-based approach of
Graphene is similar to Django
Mapping models to types

20. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Lesson 2
Mutations can be tricky

21. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Example mutation in Graphene

22. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Example mutation in Graphene
input

23. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Example mutation in Graphene
output

24. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
mutation resolver
Example mutation in Graphene

25. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
● No input data validation
● No unified errors
● A lot of boilerplate if you
have many similar
mutations
Example mutation in Graphene

26. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Abstractions to the rescue 🎉

27. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Unified errors

28. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
● Base building block for
all mutations
● Unified errors structure
● Errors are included in the
schema
Unified errors

29. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
CRUD API pattern
A lot of mutations follow the same pattern

30. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
CLEAN INPUT
DATA
CRUD API pattern
A lot of mutations follow the same pattern

31. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
CLEAN INPUT
DATA
CRUD API pattern
A lot of mutations follow the same pattern
CREATE MODEL
INSTANCE

32. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
CLEAN INPUT
DATA
CRUD API pattern
A lot of mutations follow the same pattern
CREATE MODEL
INSTANCE
VALIDATE

33. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
CLEAN INPUT
DATA
CRUD API pattern
A lot of mutations follow the same pattern
CREATE MODEL
INSTANCE
VALIDATE SAVE CHANGES
IN DATABASE

34. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Model mutation to create an object

35. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Model mutation to create an object

36. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Lesson 3
No native support for subscriptions

37. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
● Django was designed for request-response pattern
● It’s internally synchronous (e.g. database access)
● Possible to support async requests with Django Channels
○ @database_sync_to_async
● Requires third-party libraries

38. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Lesson 4
Additional libraries

39. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
● JWT authentication and permissions
● Apollo Federation
● File upload
You need additional libraries to build a fully-fledged API:
● Query cost analysis
But some features are not implemented at all:

40. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Last but not least...

41. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Why do you use Python?

42. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
❤

43. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
A resolver in Ariadne
Modern Python is asynchronous

44. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Source: https://stackoverflow.blog/2017/09/06/incredible-growth-python/

45. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
Ariadne is a Python library for implementing
schema-first GraphQL servers. It is simple to
use and open for extension.
● Schema-first approach
● Asynchronous execution
● Inspired by Apollo Server
ariadnegraphql.org

46. COPYRIGHT © 2009–2019 MIRUMEE SOFTWARE
THANK YOU!
@maarcingebala