In C#, Can I make my Azure Function App more DRY?

Question

I have a Function App composed in C#.

It has a bunch of classes like:

public class InitialUploadNewOrModifiedFileTaskEventGenerator
{
    private readonly TaskEventGeneratorConfig _taskEventGeneratorConfig;
    private readonly NewOrModifiedFileTaskEventGeneratorHelper _taskEventGeneratorHelper;

    private const string _configName = TaskEventGeneratorSettingNames.InitialUpload;

    public InitialUploadNewOrModifiedFileTaskEventGenerator(
            ITaskEventGeneratorConfigFactory taskEventGeneratorConfigFactory,
            NewOrModifiedFileTaskEventGeneratorHelper taskEventGeneratorHelper
        )
    {
        _taskEventGeneratorConfig = Guard.Against.Null(taskEventGeneratorConfigFactory)
            .GetConfig(_configName);
        _taskEventGeneratorHelper = Guard.Against.Null(taskEventGeneratorHelper);
    }

    [FunctionName($"GenerateFor{_configName}")]
    [SuppressMessage("Roslynator", "RCS1163:Unused parameter.", Justification = "Used for Azure Function")]
    public async Task Generate(
        [TimerTrigger($"%{_configName}:DirectoryScanFrequencyCron%")] TimerInfo timer,
        CancellationToken cancellationToken
    ) =>
        await _taskEventGeneratorHelper.Generate(_taskEventGeneratorConfig, cancellationToken);
}

Which are identical in all but 2 things:

1. The class name.
2. The value of const string _configName.

The values of _taskEventGeneratorConfig and $"%{_configName}:DirectoryScanFrequencyCron%" both come from the appsettings file.

At present, each time we want to add a new configuration with a new frequency, we need to hardcode another class and add constant value in TaskEventGeneratorSettingNames.

Is there a way we can do the same thing only having one Generate method? (I'm thinking some sort of metaprogramming to generate a series of classes from a single class?)

Would it be possible to go a step further and include all the configurations, including the cron frequencies within an array in the appsettings, and then not even need to hardcode config name values anywhere?

Answer 1

Functions apps need to define their functions statically, so the host knows all the triggers that need to be set up. With this constraint, your solution must be compile-time. Appsettings is a runtime solution.

Compile-time generation has historically been a weak point for C#, but these days we have source generators. They're not hard to write, and they can key off of a special file like timedtasks.json.