Pipeline: Field

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

Defining the Fields Pipeline

The fields 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 fields 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 fieldsPipeline = builder.Build();

In this example, the fields 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 Fields Pipeline

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

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 fieldsPipeline(queryContext);

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

Console.WriteLine(result.Data);

In this example, the fields pipeline is used to process a GraphQL field. The fieldsPipeline 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