# GraphQL Remote Loader
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Performant, batched GraphQL queries from within the resolvers of a [`graphql-ruby`](https://github.com/rmosolgo/graphql-ruby) API.


## Snippet

```ruby
field :login, String, null: false, description: "The currently authenticated GitHub user's login."

def login
  GitHubLoader.load("viewer { login }").then do |results|
    if results["errors"].present?
      ""
    else
      results["data"]["viewer"]["login"].upcase
    end
  end
end
```

## Description
`graphql-remote_loader` allows for querying GraphQL APIs from within resolvers of a [`graphql-ruby`](https://github.com/rmosolgo/graphql-ruby) API. 

This can be used to create GraphQL APIs that depend on data from other GraphQL APIs, either remote or local.

A promise-based resolution strategy from Shopify's [`graphql-batch`](https://github.com/Shopify/graphql-batch) is used to batch all requested data into a single GraphQL query. Promises are fulfilled with only the data they requested.

You can think of it as a lightweight version of schema-stitching.

## Performance

Each `Loader#load` invocation does not send a GraphQL query to the remote. The Gem uses graphql-batch to collect all GraphQL queries together, then combines them and sends a single query to the upstream. The gem splits the response JSON up so that each promise is only resolved with data that it asked for.

## How to use
First, you'll need to install the gem. Either do `gem install graphql-remote_loader` or add this to your Gemfile:

```
gem "graphql-remote_loader"
```

The gem provides a base loader `GraphQL::RemoteLoader::Loader` which does most of the heavy lifting. In order to remain client-agnostic, there's an unimplemented no-op that takes a query string and queries the remote GraphQL API.

To use, create a new class that inherits from `GraphQL::RemoteLoader::Loader` and define `def query(query_string)`. The method takes a query String as input. The expected output is a response `Hash`, or an object that responds to `#to_h`.

Example:

```ruby
require "graphql/remote_loader"

module MyApp
  class GitHubLoader < GraphQL::RemoteLoader::Loader
    def query(query_string)
      parsed_query = GraphQLClient.parse(query_string)
      GraphQLClient.query(parsed_query)
    end
  end
end
```

This example uses [`graphql-client`](https://github.com/github/graphql-client). Any client, or even just plain `cURL`/`HTTP` can be used.

With your loader setup, you can begin using `#load` or `#load_value` in your `graphql-ruby` resolvers.

## Full example

To see a working example of how `graphql-remote_loader` works, see the [complete, working example application](https://github.com/d12/graphql-remote_loader_example).

## Running tests

```
bundle install
bundle exec rspec
```