Pipeline: Resolver

The resolvers pipeline is a series of middleware components that process a GraphQL resolver. Each middleware component in the pipeline has the opportunity to inspect, modify, or short-circuit the resolver and response. The pipeline is defined using the FieldDelegateBuilder class.

Defining the Resolvers Pipeline

The resolvers pipeline is defined using the FieldDelegateBuilder class. The FieldDelegateBuilder class provides methods for adding middleware components to the pipeline. The following example shows how to define a simple resolvers pipeline:

var builder = new FieldDelegateBuilder();

builder.Use(next => async context =>
{
    // Middleware component 1
    Console.WriteLine("Before Middleware 1");
    await next(context);
    Console.WriteLine("After Middleware 1");
});

builder.Use(next => async context =>
{
    // Middleware component 2
    Console.WriteLine("Before Middleware 2");
    await next(context);
    Console.WriteLine("After Middleware 2");
});

var resolversPipeline = builder.Build();

In this example, the resolvers pipeline consists of two middleware components. Each middleware component writes a message to the console before and after calling the next middleware component in the pipeline.

Using the Resolvers Pipeline

The resolvers pipeline is used to process a GraphQL resolver. The following example shows how to use the resolvers pipeline to process a GraphQL resolver:

var schema = new Schema();
var executor = new Executor(schema);

var request = new GraphQLRequest
{
    Query = new ExecutableDocument
    {
        Definitions = new List<IDefinition>
        {
            new OperationDefinition
            {
                Operation = OperationType.Query,
                SelectionSet = new SelectionSet
                {
                    Selections = new List<ISelection>
                    {
                        new FieldSelection
                        {
                            Name = new Name("hello")
                        }
                    }
                }
            }
        }
    }
};

var queryContext = executor.BuildQueryContextAsync(request);
await resolversPipeline(queryContext);

var result = await queryContext.Response.SingleAsync();

Console.WriteLine(result.Data);

In this example, the resolvers pipeline is used to process a GraphQL resolver. The resolversPipeline delegate is called with the queryContext object, which contains the GraphQL request and other context information. The queryContext.Response property contains the response stream, which is an IAsyncEnumerable<ExecutionResult>.

Next