Pipeline: SelectionSet

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

Defining the Selection Sets Pipeline

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

var builder = new SelectionSetPipelineBuilder();

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 selectionSetPipeline = builder.Build();

In this example, the selection sets 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 Selection Sets Pipeline

The selection sets pipeline is used to process a GraphQL selection set. The following example shows how to use the selection sets pipeline to process a GraphQL selection set:

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 selectionSetPipeline(queryContext);

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

Console.WriteLine(result.Data);

In this example, the selection sets pipeline is used to process a GraphQL selection set. The selectionSetPipeline 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>.

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