# Remote schemas

Hasura gives you CRUD + realtime GraphQL APIs with authorization & access control. However, in many cases, you will need to write APIs (queries, mutations) that contain custom logic. For example, implementing a payment API, or querying data that is not in your database.

Hasura has the ability to merge remote GraphQL schemas and provide a unified GraphQL API. Think of it like automated schema merging. All you need to do is build your own GraphQL service and then provide the HTTP endpoint to Hasura. Your GraphQL service can be written in any language or framework.

Remote schemas are ideal for use cases such as:

* Customizing mutations (*e.g. running validations before inserts*)
* Supporting features like payments, etc. and providing a consistent interface to access them i.e. behind the GraphQL Engine's API
* Fetching disparate data from other sources (*e.g. from a weather API or another database*)

To support custom business logic, you'll need to create a custom GraphQL server (see [boilerplates](community/boilerplates/remote-schemas)) and merge its schema with GraphQL Engine's.

![remote schems architecture](assets/remote-schemas-arch.png)

## Demo (*40 seconds*)

[![video demo of merging remote schemas](https://img.youtube.com/vi/eY4n9aPsi0M/0.jpg)](https://www.youtube.com/watch?v=eY4n9aPsi0M)

[Merge remote GraphQL schemas (YouTube link)](https://youtu.be/eY4n9aPsi0M)

[Adding a remote schema ](https://youtu.be/01t4t2t4q1c)

## Quickstart

The fastest way to try remote schema out is via Heroku.

1. Click on the following button to deploy GraphQL Engine on Heroku with the free Postgres add-on:

    [![Deploy to Heroku](https://www.herokucdn.com/deploy/button.svg)](https://heroku.com/deploy?template=https://github.com/hasura/graphql-engine-heroku)

2. Open the Hasura console

   Visit `https://<app-name>.herokuapp.com` (*replace \<app-name\> with your app name*) to open the admin console.

3. Merge your first remote schema and query it

   In the admin console, open the ``Remote Schemas`` tab and click on the ``Add`` button. Fill in the following details:
   * Remote Schema name: ``countries`` (*an alias for this remote schema*).
   * GraphQL server URL: ``https://countries.trevorblades.com/`` (*a public GraphQL API that we'll use to quickly check out this feature; maintained by [@trevorblades](https://github.com/trevorblades)*. 
   * Ignore the remaining configuration settings and click on the ``Add Remote Schema`` button.

   Head to the ``GraphiQL` tab and run the following query (*paste it in the query window on the left and click the* ▶️ *(play) button*):

   ```graphql
   {
      countries {
        emoji
        name
        languages {
          name
          native
        }
      }
   }
   ```

   You can explore the GraphQL types from the remote schema using the ``Docs`` explorer in the top right corner of the ``GraphiQL`` interface.

## Boilerplates

Boilerplates for custom GraphQL servers in popular languages/frameworks are available.

* [Regular boilerplates](community/boilerplates/graphql-servers) that can be deployed anywhere.
* [Serverless boilerplates](https://github.com/hasura/graphql-serverless) that can be deployed on serverless platforms like AWS Lambda, etc.

Please note that boilerplates for more languages, frameworks, serverless platforms, etc. are being iterated upon and community contributions are very welcome. 


## Caveats

**Current limitations**:

* Nomenclature: Type names and node names need to be unique across all merged schemas (case-sensitive match). In the next few iterations, support for merging types with the same name and structure will be available.
* Nodes from different GraphQL servers cannot be used in the same query/mutation. All top-level nodes have to be from the same GraphQL server.
* Subscriptions on remote GraphQL server are not supported.

These limitations will be addressed in upcoming versions.

## Documentation

Read the complete [documentation](https://hasura.io/docs/latest/graphql/core/remote-schemas/index.html).

## Translations

This document is available in the following translations:

- [French :fr:](translations/remote-schemas.french.md)
- [Hindi  :india:](translations/remote-schemas.hindi.md)