FastAPI example

Project Setup

This project folder structure is like the below.

modelresolvers-fastapi-example
├── main.py
├── models
│   └── user.py
├── Pipfile
├── Pipfile.lock
└── resolvers
    └── user.py

Create a virtual environment with pipenv. Since modelresolvers requires Python3.10 we create virtual env by specify Python version

pipenv --python 3.10

Install dependencies

pipenv install fastapi modelresolvers uvicorn

Activate virtual environment

pipenv shell

Define User model

Create user.py under models folder

Import strawberry module to define GraphQL type

import strawberry

Create User model

@strawberry.type
class User:
    id: int | None
    firstname: str
    lastname: str

Since the model is a strawberry GraphQL type it must be decorated with strawberry.type decorator.

id field is optional because we want to set it automatically instead of getting it from the client.

The entire file code

import strawberry


@strawberry.type
class User:
    id: int | None
    firstname: str
    lastname: str

Resolvers

Create user.py under resolvers folder

Import modelresolvers

from modelresolvers import ModelResolvers

Import the User model that we just created

from models.user import User

Create ModelResolvers instance for user model resolvers

user_resolvers = ModelResolvers()

Since we are simulating a real-world example we just define a user list

users = [
    User(id=1, firstname="John", lastname="Doe"),
    User(id=2, firstname="Jane", lastname="Doe"),
]

Querying a single user

@user_resolvers.query(name="user")
def user(id: int) -> User | None:
    return next((user for user in users if id == user.id), None)

To make a function a query we decorate it with the query decorator of ModelResolvers instance. The name of the query decorator parameter is optional. The default is the function name that is decorated which in this case is user. The function parameters and return parameter type should be specified by type hints otherwise the strawberry raises error. The user function searches the user based on the id it is not found it then returns None

@user_resolvers.query(name="users")
def get_users() -> list[User]:
    return users

get_users query returns all users available in the users list. Pay close attention to the function name and the name argument of the query decorator. They are different. get_users query will be displayed as users in the GraphQL client UI.

Another ModelResolvers decorator is mutation.

@user_resolvers.mutation(name="add_user")
def add_user(firstname: str, lastname: str) -> User:
    user = User(id=len(users) + 1, firstname=firstname, lastname=lastname)
    users.append(user)
    return user

firstname and lastname pass by GraphQL client. The id field is set on the backend side. It is calculated as users list length plus 1. Then the created user returns to the client.

The entire file code

from modelresolvers import ModelResolvers

from models.user import User


user_resolvers = ModelResolvers()

users = [
    User(id=1, firstname="John", lastname="Doe"),
    User(id=2, firstname="Jane", lastname="Doe"),
]


@user_resolvers.query(name="user")
def user(id: int) -> User | None:
    return next((user for user in users if id == user.id), None)


@user_resolvers.query(name="users")
def get_users() -> list[User]:
    return users


@user_resolvers.mutation(name="add_user")
def add_user(firstname: str, lastname: str) -> User:
    user = User(id=len(users) + 1, firstname=firstname, lastname=lastname)
    users.append(user)
    return user

Main file

Create main.py file

Import Schema module from modelresolvers package

from modelresolvers import Schema

Import FastAPI module from fastapi package

from fastapi import FastAPI

Import GraphQLRouter module from strawberry package

from strawberry.fastapi import GraphQLRouter

Import resolvers instance you have just created

from resolvers.user import user_resolvers

When you create an modelresolvers Schema it will also create a strawberry schema as modelresolvers is based on strawberry At this point, we need to strawberry schema rather than modelresolvers Schema. We get strawberry schema from modelresolvers schema

schema = Schema(models_resolvers=[user_resolvers]).strawberry_schema

Create GraphQL router

graphql_app = GraphQLRouter(schema)

Create fastapi app and add GraphQL router to the app

app = FastAPI()
app.include_router(graphql_app, prefix="/graphql")

The entire file code

from modelresolvers import Schema

from fastapi import FastAPI
from strawberry.fastapi import GraphQLRouter

from resolvers.user import user_resolvers

schema = Schema(models_resolvers=[user_resolvers]).strawberry_schema

graphql_app = GraphQLRouter(schema)

app = FastAPI()
app.include_router(graphql_app, prefix="/graphql")

Run the application

uvicorn main:app --reload

Go to http://127.0.0.1:8000/graphql and run queries and mutations