Azure functions - should functions be written inside static classes

Question

I'm starting to try out Azure functions. I'm using Visual Studio 2017 Preview version 15.3. When I right click on the Azure Functions project I created, and select Add>New Item...>Azure Function, the default template Visual Studio generates is of a public static class with a public static async Task method (the function).

Does the class need to be static (I changed it to non-static and it seems to work)? Is that a best practice for Azure functions? If that is the case, what problems might rise by using a non-static class to hold the Azure Function method?

score 32 · Answer 1 · edited Apr 14 '21 at 14:45

As always it depends. Among other answers which stay to keep function class static, I would like to present another case where the non-static class can be helpful. Please look at: Functions dependency injection. If you want use DI inside your functions there is no easy way to do it with static class because it's can not have instance constructors with parameters. So you are not able to write something like this:

public class HttpTrigger
{
    private readonly IMyService _service;
    private readonly HttpClient _client;

    public HttpTrigger(IMyService service, IHttpClientFactory httpClientFactory)
    {
        _service = service;
        _client = httpClientFactory.CreateClient();
    }

    [FunctionName("GetPosts")]
    public async Task<IActionResult> Get(
        [HttpTrigger(AuthorizationLevel.Function, "get", Route = "posts")] HttpRequest req,
        ILogger log)
    {
        log.LogInformation("C# HTTP trigger function processed a request.");
        var res = await _client.GetAsync("https://microsoft.com");
        await _service.AddResponse(res);

        return new OkResult();
    }
}

Yes it is definitely safe. Instantiating a class per request is not an issue. This is considered best practice for Azure Functions in my opinion. — Niels Brinch, Dec 30 '20 at 11:46
Finally! a way to enforce not using factory pattern! Rather not use DI if factories are involved — TamusJRoyce, Mar 10 '23 at 14:14

score 6 · Answer 2 · edited Jun 21 '19 at 15:20

6

Given that the functions are invoked in a serverless fashion, static methods have the correct semantics here, i.e., you should assume the process can exit after every function invocation, and so you shouldn't be accumulating state on instance methods in between function invocations.

That said, we are investigating Dependency Injection.

edited Jun 21 '19 at 15:20

bubbleking

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answered Jul 18 '17 at 16:47

Mike S

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score -4 · Accepted Answer · edited Jun 20 '19 at 23:06

Does the class need to be static (I changed it to non-static and it seems to work)? Is that a best practice for Azure functions?

A static class can only contain static members, and it can't be instantiated. Changing the class to non-static will allow you to add non-static members and create an instance of this class.

Please check whether you need to add non-static members to, or create an instance of, this class. Due to the Single Responsibility Principle, which states that every class should have responsibility over a single part of the functionality provided by the software, I suggest you create a new class and put the non-static members there.

If that is the case, what problems might rise by using a non-static class to hold the Azure Function method?

I suppose the reason you want to use a non-static class is that you want to create some non-static members in it. Doing so will make your class complex and difficult to maintain.

My final answer is that the class can be changed to non-static. To keep the class simple, I suggest you keep the class static.

_I suppose the reason you want to use a non-static class is that you want to create more non-static members in the class. It will make your class complex and difficult to maintain._ Probably not, and absolutely not. Remembering state in an instance does not automatically make that code complex. Static classes and methods themselves are generally more difficult to unit test, and can make an instance that uses them **significantly** more difficult to unit test. — StingyJack, Feb 12 '19 at 20:26
@amor This doesn't answer the question. You haven't addressed the key detail about static vs instance as related to Azure Functions. — Matthew, Sep 26 '20 at 00:36

Azure functions - should functions be written inside static classes

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