Edit

Write your mutation resolvers

If you plan to build an application, most of the time you will need to provide a way to create, update and delete data over your API. In the REST-full world, this operations are available through some exposed endpoints available on the different POST, PUT, PATCH and DELETE HTTP methods. In the GraphQL world, all the actions which mutate the data are available behind the mutation operation.

The mutation operation type looks like the query one but with a major difference in the way of being executed. While root fields of a query operation are executed and resolved in parallel, in a mutation operation, root fields are executed in serial order.

Write code

In our case, we would like to be able to update a recipe. Thus, we will expose a field to update a recipe, either its name or/and cooking time.

First, we will start to define the Mutation schema part:

recipes_manager/sdl/Mutation.graphql

input RecipeInput {
  id: Int!
  name: String
  cookingTime: Int
}

type Mutation {
  updateRecipe(input: RecipeInput!): Recipe!
}

recipes_manager/mutation_resolvers.py

And now the resolver which is in charge of updating the recipe metadata:

from typing import Any, Dict, Optional

from tartiflette import Resolver

from recipes_manager.data import RECIPES


@Resolver("Mutation.updateRecipe")
async def resolve_mutation_update_recipe(
    parent: Optional[Any],
    args: Dict[str, Any],
    ctx: Dict[str, Any],
    info: "ResolveInfo",
) -> Dict[str, Any]:
    """
    Resolver in charge of the mutation of a recipe.
    :param parent: initial value filled in to the engine `execute` method
    :param args: computed arguments related to the mutation
    :param ctx: context filled in at engine initialization
    :param info: information related to the execution and field resolution
    :type parent: Optional[Any]
    :type args: Dict[str, Any]
    :type ctx: Dict[str, Any]
    :type info: ResolveInfo
    :return: the mutated recipe
    :rtype: Dict[str, Any]
    :raises Exception: if the recipe id doesn't exist
    """
    recipe_id = args["input"]["id"]
    name = args["input"].get("name")
    cooking_time = args["input"].get("cookingTime")

    if not (name or cooking_time):
        raise Exception(
            "You should provide at least one value for either name or "
            "cookingTime."
        )

    for index, recipe in enumerate(RECIPES):
        if recipe["id"] == recipe_id:
            if name:
                RECIPES[index]["name"] = name
            if cooking_time:
                RECIPES[index]["cookingTime"] = cooking_time
            return RECIPES[index]

    raise Exception(f"The recipe < {recipe_id} > does not exist.")

Launch the app

Your Tartiflette recipes manager is now able to mutate data. Launch it with the following command and go to the next step to find out how to execute a mutation request to your GraphQL API:

python -m recipes_manager