Azure Function，依赖注入和循环

Question

I have the following code:

Startup.cs:

    services.AddTransient<ProcessPendingDeactivateDeviceStatus>();

Function code:

public class FunctionPendingDeactivationStatusesCheck
{
    private readonly IDeviceService _deviceService;
    private readonly ProcessPendingDeactivateDeviceStatus _pendingDeviceStatus;


    public FunctionPendingDeactivationStatusesCheck(
        IDeviceService deviceService,
        ProcessPendingDeactivateDeviceStatus pendingDeviceStatus)
    {
        _deviceService = deviceService;
        _pendingDeviceStatus = pendingDeviceStatus;
    }

    [Singleton]
    [FunctionName("FunctionPendingDeactivationStatusesCheck")]
    public async Task Run([TimerTrigger("0 12,27,42,57 * * * *")] TimerInfo myTimer, ExecutionContext context, ILogger log)
    {
        var pendingDeletingDevices = _deviceService.GetDevicesByStatus(DeviceStatus.PendingDeleted);

        foreach (var device in pendingDeletingDevices)
        {
            await _pendingDeviceStatus.InitAsync(device);

so, as we can see, we call InitAsync inside loop and work with the same instance for all iterations. I want to recreate this object for every iteration. How to do it?

Answer 1

A factory will be needed to get the desired behavior.

Register a factory delegate that will be used to create the instances

services.AddTransient<ProcessPendingDeactivateDeviceStatus>();
services.AddSingleton<Func<ProcessPendingDeactivateDeviceStatus>>(sp => 
    () => sp.GetRequiredService<ProcessPendingDeactivateDeviceStatus>()
);

Inject the factory and create instance as needed

public class FunctionPendingDeactivationStatusesCheck {
    private readonly IDeviceService _deviceService;
    private readonly Func<ProcessPendingDeactivateDeviceStatus> factory;
    
    public FunctionPendingDeactivationStatusesCheck(
        IDeviceService deviceService,
        Func<ProcessPendingDeactivateDeviceStatus> factory) {
        _deviceService = deviceService;
        this.factory = factory;
    }

    [Singleton]
    [FunctionName("FunctionPendingDeactivationStatusesCheck")]
    public async Task Run([TimerTrigger("0 12,27,42,57 * * * *")] TimerInfo myTimer, ExecutionContext context, ILogger log) {
        var pendingDeletingDevices = _deviceService.GetDevicesByStatus(DeviceStatus.PendingDeleted);

        foreach (var device in pendingDeletingDevices) {
            ProcessPendingDeactivateDeviceStatus  _pendingDeviceStatus = factory();
            await _pendingDeviceStatus.InitAsync(device);

            //...

Every time factory is invoked, a new transient instance will be created by the container.

Without any details as to why a new instance is needed for each iteration, there is no way to tell if there will be any adverse effects of creating that many instances in cases where there are many devices.