TechHut.Azure.Functions.Projection 8.0.1

TechHut.Azure.Functions.Projection

A lightweight library for Azure Functions that enables dynamic JSON response projection. Allow your API clients to specify which fields to include in the response using a $project specification in the request body, query string, or headers.

Features

• Flexible JSON Projection: Filter and shape JSON responses dynamically.
• Multiple Input Methods: Accepts projection via request body, query string, or headers.
• Seamless Azure Functions Integration: Designed for HTTP-triggered Azure Functions (.NET 8+).
• Easy Middleware Integration: Apply projection globally using middleware—no need to modify individual function code.

Installation

Install via NuGet Package Manager:

dotnet add package TechHut.Azure.Functions.Projection

Or via the NuGet Package Manager UI in Visual Studio.

Usage

1. Register the Middleware

Add the projection middleware in your Azure Functions application's startup code (typically in Program.cs):

using TechHut.Azure.Functions.Projection.Extensions;

var builder = FunctionsApplication.CreateBuilder(args);

builder.ConfigureFunctionsWebApplication()
	   .AddProjectionMiddleware();

builder.Build().Run();

Note:
If you need to allow synchronous IO (for certain scenarios), you can configure Kestrel as shown in the example project.

2. Write Your Function as Usual

You do not need to manually apply projection logic in your function code. Simply return your JSON response as usual:

[Function("Customers")] 
public async Task<HttpResponseData> Run([HttpTrigger(AuthorizationLevel.Function, "get", "post")] HttpRequestData req, FunctionContext executionContext) 
{ 
	var response = req.CreateResponse(HttpStatusCode.OK); 
	var jsonContent = await File.ReadAllTextAsync(@".\customers.json", Encoding.UTF8);

	response.Headers.Add("Content-Type", "application/json");

	await response.WriteStringAsync(jsonContent);

	return response;
}

The middleware will automatically intercept and apply the projection to the response if the client specifies one.

3. Client-Side Usage

Clients can specify the projection in one of three ways:

• Request Body (for application/json):

json
{ "$project": { "field1": {}, "field2": {} } }

• • Query String:

?$project={"field1":{},"field2":{}}

• • Header:

$project: {"field1":{},"field2":{}}

Example

Request:

POST /api/Customers 
Content-Type: application/json

{ 
	"$project": 
	{ 
		"name": null, 
		"age": null,
		"address": 
		[
			{
				"street": null,
				"postcode": null
			}
		]
	} 
}

Response:

json
{ "name": "Alice", "age": 30 }

Requirements

• .NET 8 or later
• Azure Functions v4 or later

License

LICENSE