Using GraphQL in Azure API Management–Part 2

We’ll continue our exploration of the GraphQL features in Azure API Management by having a look at another feature; the possibility to transform an existing SOAP or REST API in an GraphQL API(Synthetic GraphQL). (If you missed the previous post in this series, have a look here.) Let's walk through the steps.

The REST API

Let’s first have a look at our REST API that we’ll use in this post. I’ve created an Azure Function that can be called through a GET request and returns a Person object(similar to the GraphQL API I used in the previous post).

Here is the related code:

	public class RestFunction
	{
	private readonly ILogger<RestFunction> _logger;
	public RestFunction(ILogger<RestFunction> log)
	{
	_logger = log;
	}
	[FunctionName("GetPerson")]
	[OpenApiOperation(operationId: "GetPerson")]
	[OpenApiResponseWithBody(statusCode: HttpStatusCode.OK, contentType: "text/plain", bodyType: typeof(Person), Description = "The OK response")]
	public async Task<IActionResult> Run(
	[HttpTrigger(AuthorizationLevel.Anonymous, "get", "post", Route = null)] HttpRequest req)
	{
	_logger.LogInformation("C# HTTP trigger function processed a request.");
	return new OkObjectResult(new Person("Luke Skywalker"));
	}
	}

view raw RestFunction.cs hosted with ❤ by GitHub

Create a Synthetic GraphQL API

Let’s see how we can expose this REST API as a ‘Synthetic GraphQL’ API through Azure API Management.

• Go to your Azure API Management instance in the Azure portal.
• From the side menu, select APIs in the APIs section:

• Choose Synthetic GraphQL under Define a new API:

• In the dialog box specify the following fields:
  • Display name: The name you want to use to recognize your API
  • Name: Autogenerated based on the display name
  • Schema file: The GraphQL schema that will be exposed through this endpoint

• In this example, I’ll use the following GraphQL schema:

	type Query {
	person: Person
	}
	type Person {
	name: String
	}

view raw schema.graphql hosted with ❤ by GitHub

• Click on Create to import the GraphQL schema.
• After the API is imported you can browse the schema on the Design tab:

Of course right now there isn’t anything useful with this API as it isn’t linked to our existing REST API.  To change this, we have to create a set-graphql-resolver policy to map a field in the schema to an existing HTTP endpoint.

• In the Backend processing section, select the Backend Policy code editor:

• Configure the set-graphql-resolver policy to resolve our REST api using an HTTP data source:

	<set-graphql-resolver parent-type="Query" field="person">
	<http-data-source>
	<http-request>
	<set-method>GET</set-method>
	<set-url>https://restfunctionapp20220807115633.azurewebsites.net/api/GetPerson</set-url>
	</http-request>
	</http-data-source>
	</set-graphql-resolver>

view raw SetResolver.xml hosted with ❤ by GitHub

• Click on Save to apply the policy.

• To test our API endpoint, go to the Test tab. Select the fields you want to fetch or write your GraphQL query from scratch:

More information: https://docs.microsoft.com/en-us/azure/api-management/graphql-schema-resolve-api