Creating actions
================

.. contents:: Table of contents
  :backlinks: none
  :depth: 1
  :local:

Introduction
------------

An action is a GraphQL mutation. You have to define the GraphQL type of the
arguments that the mutation accepts and the GraphQL type of the its response.

To create an action, you have to:

1. Define the mutation
2. Define the required types
3. Create a handler

**For example**, let's start with a basic mutation that accepts a list of numbers and returns
their sum. We'll call this mutation ``addNumbers``.

Step 0: Setup
-------------

.. rst-class:: api_tabs
.. tabs::

  .. tab:: CLI

     :ref:`Install <install_hasura_cli>` the latest version of Hasura CLI.

     You can either get started with an existing project or create a new project.

     **For a new project**

     .. code-block:: bash

         hasura init

     This will create a new project. You can set up your GraphQL engine endpoint
     (and admin secret if it exists) in the ``config.yaml``.

     Run ``hasura metadata export`` so that you get server's metadata into the
     ``metadata/`` directory.

     **For existing projects**

     Actions are supported only in the v2 config of the CLI. Check the ``config.yaml``
     of your Hasura project for the ``version`` key.

     If you are in ``version: 1``, actions commands are not supported. Upgrade to
     version 2 by running:

     .. code-block:: bash

         hasura scripts update-config-v2

     Run ``hasura metadata export`` so that you get server's metadata into the
     ``metadata/`` directory.


Step 1: Define your mutation and associated types
-------------------------------------------------

.. rst-class:: api_tabs
.. tabs::

  .. tab:: Console

     Go to the ``Actions`` tab on the console and click on ``Create``. This will
     take you to a page like this:

     .. thumbnail:: ../../../img/graphql/manual/actions/action-create-page.png
        :alt: Console action create

     Define the action as follows in the ``Action Definition`` editor.

     .. code-block:: graphql

        type Mutation {
          addNumbers (numbers: [Int]): AddResult
        }

     In the above action, we called the returning object type to be ``AddResult``.
     Define it in the ``New types definition`` as:

     .. code-block:: graphql

        type AddResult {
          sum: Int
        }

  .. tab:: CLI

     To create an action, run

     .. code-block:: bash

         hasura actions create addNumbers

     This will open up an editor with ``metadata/actions.graphql``. You can enter
     the action's mutation definition and the required types in this file. For your
     ``addNumbers`` mutation, replace the content of this file with the following
     and save:

     .. code-block:: graphql

        type Mutation {
          addNumbers (numbers: [Int]): AddResult
        }

        type AddResult {
          sum: Int
        }

The above definition means:

* This action will be available in your GraphQL schema as a mutation called ``addNumbers``
* It accepts an argument called ``numbers`` which is a list of integers.
* It returns an output type called ``AddResult``.
* ``AddResult`` is a simple object type with a field called ``sum`` of type integer.

Step 2: Create the action handler
---------------------------------

A handler is an HTTP webhook where you can perform the custom logic for the
action. In this case, it is the addition of the numbers. NodeJS/Express code
for this handler would look something like:

.. code-block:: js

    const handler = (req, resp) => {
      // You can access ther arguments input at req.body.input
      const { numbers } = req.body.input;

      // perform your custom business logic
      // return an error or response
      try {
        return resp.json({
          sum: numbers.reduce((s, n) => s + n, 0)
        });
      } catch(e) {
        console.error(e)
        return resp.status(500).json({
          message: 'unexpected'
        })
      }
    };

You can deploy this code somewhere and get URI. For getting started quickly, we
also have this handler ready at ``https://hasura-actions-starter-kit.glitch.me/addNumbers``.

Set the handler
***************

Now, set the handler for the action:

.. rst-class:: api_tabs
.. tabs::

  .. tab:: Console

     Set the value of the ``handler`` field to the above endpoint.

  .. tab:: CLI

     Go to ``metadata/actions.yaml``. You must see a handler like ``http://localhost:3000``
     or ``http://host.docker.internal:3000`` under the action named ``addNumbers``.
     This is a default value taken from ``config.yaml``.

     Update the ``handler`` to the above endpoint.

Step 3: Finish action creation
------------------------------

.. rst-class:: api_tabs
.. tabs::

  .. tab:: Console

     Hit ``Create``.

  .. tab:: CLI

     Run ``hasura metadata apply``.


Step 4: Try it out
------------------

In the Hasura console, head to the ``GraphiQL`` tab and try out the new action.

.. graphiql::
  :view_only:
  :query:
    mutation MyMutation {
      addNumbers(numbers: [1, 2, 3, 4]) {
        sum
      }
    }
  :response:
    {
      "data": {
        "addNumbers": {
          "sum": 10
        }
      }
    }

And that's it. You have created your first action!