Edit

Write your resolvers

Previously, we created our application instance with a first iteration of our Schema using the SDL. Now, we're going to bind some data to our Schema, using resolvers, which are in charge of linking the Schema with your application logic.

What is a resolver?

A resolver is a function (which can be asynchronous) that is attached to a field of your Schema. It will be in charge of providing data accordingly to the fields or objects it is attached to.

How to attach a resolver to a Schema field with Tartiflette?

With Tartiflette, it is very straightforward to attach a resolver function to the Schema field.

We provide a decorator named Resolver which will attach your function to the specified Schema field.

from tartiflette import Resolver

@Resolver("Query.hello")
async def resolver_fieldname(parent, args, ctx, info):
    return {
        "foo": "bar"
    }

In this example, the function resolver_fieldname will be executed each time the field hello is called.

Note: by default, the root type name for query operations is Query so the full name of the field is Query.hello.

If you want to know more about the Resolver part, we suggest taking a look at the Resolver API documentation.

Write code

In our example, we will have 3 different resolvers.

• One which will resolve the recipes list: @Resolver("Query.recipes")
• Another which will resolve only one recipe: @Resolver("Query.recipe")
• A last one which will resolve a subfield of the Recipe object, the ingredients: @Resolver("Recipe.ingredients")

filename: recipes_manager/query_resolvers.py

import collections

from tartiflette import Resolver

from recipes_manager.data import INGREDIENTS, RECIPES


@Resolver("Query.recipes")
async def resolve_recipes(parent, args, ctx, info):
    return RECIPES


@Resolver("Query.recipe")
async def resolve_recipe(parent, args, ctx, info):
    recipe = [r for r in RECIPES if r["id"] == int(args["id"])]

    if not recipe:
        return None

    return recipe[0]


@Resolver("Recipe.ingredients")
async def resolve_ingredients(parent, args, ctx, info):
    if parent and parent["id"] in INGREDIENTS:
        return INGREDIENTS[parent["id"]]

    return None

Launch the app

Your Recipes Manager GraphQL API is now able to return data. Launch it with the following command and go to the next step to find out how to query your GraphQL API.

$ python -m recipes_manager
======== Running on http://0.0.0.0:8080 ========
(Press CTRL+C to quit)