C#•8mo ago

✅ How Scope lifetime works

I have a web api where when requesting a create endpoint, it afterwards sends an email to that person about that creation. I send email with html and for it i first check if that html was read before and then store it in a variable to improve efficiency (to not read every single time). I have that as AddTransiant, which means that besides i store that in a variable, it still has to be lost, because of a lifetime. But it doesn't, it still knows that. Can someone explain how that lifetime works?

11 Replies

DachiOP•8mo ago

c#
    private  async Task<string> GetHtml(string username, string message)
    {
        if (_cachedHtml != null) return _cachedHtml.Replace("[username]", username).Replace("[message]", message);
        var path = GetPathToEmailHtml();
        using var reader = new StreamReader(path);
        _cachedHtml = await reader.ReadToEndAsync();

        return _cachedHtml.Replace("[username]", username).Replace("[message]", message);
    }

c#
    private  async Task<string> GetHtml(string username, string message)
    {
        if (_cachedHtml != null) return _cachedHtml.Replace("[username]", username).Replace("[message]", message);
        var path = GetPathToEmailHtml();
        using var reader = new StreamReader(path);
        _cachedHtml = await reader.ReadToEndAsync();

        return _cachedHtml.Replace("[username]", username).Replace("[message]", message);
    }

Here's full code if needed

c#
public class EmailSender : IEmailSender
{
    private readonly EmailConfig _emailConfig;
    private string? _cachedHtml;

    public EmailSender(IOptions<Config> emailConfig)
    {
        _emailConfig = emailConfig.Value.EmailConfig;
    }

    public async Task SendEmail(string subject, string toEmail, string username, string message)
    {
        var apiKey = _emailConfig.ApiKey;
        var client = new SendGridClient(apiKey);
        var from = new EmailAddress(_emailConfig.FromEmail, "FeatureVotingSystem");
        var to = new EmailAddress(toEmail, username);
        var plainTextContent = message;
        var htmlContent = await GetHtml(username, message);
        var msg = MailHelper.CreateSingleEmail(from, to, subject, plainTextContent, htmlContent);

        await client.SendEmailAsync(msg);
    }

    private  async Task<string> GetHtml(string username, string message)
    {
        if (_cachedHtml != null) return _cachedHtml.Replace("[username]", username).Replace("[message]", message);
        var path = GetPathToEmailHtml();
        using var reader = new StreamReader(path);
        _cachedHtml = await reader.ReadToEndAsync();

        return _cachedHtml.Replace("[username]", username).Replace("[message]", message);
    }

    private static string GetPathToEmailHtml()
    {
        var baseDirectoryPath = Directory.GetParent(Directory.GetCurrentDirectory())!.FullName;
        var parentDirectoryPath = Directory.GetParent(Directory.GetCurrentDirectory())!.Name;
        var workerPath = string.Concat(parentDirectoryPath, ".Worker");
        var path = Path.Combine(baseDirectoryPath, workerPath, "EmailContext", "index.html");

        return path;
    }
}

c#
public class EmailSender : IEmailSender
{
    private readonly EmailConfig _emailConfig;
    private string? _cachedHtml;

    public EmailSender(IOptions<Config> emailConfig)
    {
        _emailConfig = emailConfig.Value.EmailConfig;
    }

    public async Task SendEmail(string subject, string toEmail, string username, string message)
    {
        var apiKey = _emailConfig.ApiKey;
        var client = new SendGridClient(apiKey);
        var from = new EmailAddress(_emailConfig.FromEmail, "FeatureVotingSystem");
        var to = new EmailAddress(toEmail, username);
        var plainTextContent = message;
        var htmlContent = await GetHtml(username, message);
        var msg = MailHelper.CreateSingleEmail(from, to, subject, plainTextContent, htmlContent);

        await client.SendEmailAsync(msg);
    }

    private  async Task<string> GetHtml(string username, string message)
    {
        if (_cachedHtml != null) return _cachedHtml.Replace("[username]", username).Replace("[message]", message);
        var path = GetPathToEmailHtml();
        using var reader = new StreamReader(path);
        _cachedHtml = await reader.ReadToEndAsync();

        return _cachedHtml.Replace("[username]", username).Replace("[message]", message);
    }

    private static string GetPathToEmailHtml()
    {
        var baseDirectoryPath = Directory.GetParent(Directory.GetCurrentDirectory())!.FullName;
        var parentDirectoryPath = Directory.GetParent(Directory.GetCurrentDirectory())!.Name;
        var workerPath = string.Concat(parentDirectoryPath, ".Worker");
        var path = Path.Combine(baseDirectoryPath, workerPath, "EmailContext", "index.html");

        return path;
    }
}

cap5lut•8mo ago

in asp.net a scope is created for request, thus for caching between different requests u would need something that has a singleton lifetime

DachiOP•8mo ago

no, sure i added that as transiant to learn difference but it works regardless of that type i add it

cap5lut•8mo ago

with the transient lifetime its a bit different, its used when everything that gets it injected needs its own instance. eg if u have a transient service T and the services A and B and both get T injected, they dont share the same instance of T singleton = one per application lifetime scoped = one per scope the application created (in asp.net core thats per request, in another application u might create scopes differently) transient = one per injection target

DachiOP•8mo ago

that's what i am tyring to prove but making it transient by that login in the GetHtml this has to be always false if (_cachedHtml != null) return _cachedHtml.Replace("[username]", username).Replace("[message]", message); because that instanse is being renewed every single request but it doesn't

cap5lut•8mo ago

so EmailSender is registered as transient? how do u use that instance?

DachiOP•8mo ago

c#
public class EmailWorker : BackgroundService
{
    private readonly WorkerConfig _workerConfig;
    private readonly IGetQueuedEmailsRepository _getQueuedEmailsRepository;
    private readonly IUpdateEmailQueueStatusRepository _updateEmailQueueStatusRepository;
    private readonly IEmailSender _emailSender;

    public EmailWorker(
        IOptions<Config> config,
        IGetQueuedEmailsRepository getQueuedEmailsRepository,
        IUpdateEmailQueueStatusRepository updateEmailQueueStatusRepository,
        IEmailSender emailSender
    )
    {
        _workerConfig = config.Value.WorkerConfig;
        _getQueuedEmailsRepository = getQueuedEmailsRepository;
        _updateEmailQueueStatusRepository = updateEmailQueueStatusRepository;
        _emailSender = emailSender;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        while (!stoppingToken.IsCancellationRequested)
        {
            var queue = await _getQueuedEmailsRepository.GetQueuedEmails();

            foreach (var item in queue)
            {
                try
                {
                    await _emailSender.SendEmail(item.SubjectName, item.Email, item.UserName, item.EmailText);
                }
                catch (Exception ex)
                {
                    throw new Exception(ex.Message);
                }

                await _updateEmailQueueStatusRepository.UpdateEmailQueueStatus(item.Id);
            }

            await Task.Delay(_workerConfig.DelayInSeconds, stoppingToken);
        }
    }
}

c#
public class EmailWorker : BackgroundService
{
    private readonly WorkerConfig _workerConfig;
    private readonly IGetQueuedEmailsRepository _getQueuedEmailsRepository;
    private readonly IUpdateEmailQueueStatusRepository _updateEmailQueueStatusRepository;
    private readonly IEmailSender _emailSender;

    public EmailWorker(
        IOptions<Config> config,
        IGetQueuedEmailsRepository getQueuedEmailsRepository,
        IUpdateEmailQueueStatusRepository updateEmailQueueStatusRepository,
        IEmailSender emailSender
    )
    {
        _workerConfig = config.Value.WorkerConfig;
        _getQueuedEmailsRepository = getQueuedEmailsRepository;
        _updateEmailQueueStatusRepository = updateEmailQueueStatusRepository;
        _emailSender = emailSender;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        while (!stoppingToken.IsCancellationRequested)
        {
            var queue = await _getQueuedEmailsRepository.GetQueuedEmails();

            foreach (var item in queue)
            {
                try
                {
                    await _emailSender.SendEmail(item.SubjectName, item.Email, item.UserName, item.EmailText);
                }
                catch (Exception ex)
                {
                    throw new Exception(ex.Message);
                }

                await _updateEmailQueueStatusRepository.UpdateEmailQueueStatus(item.Id);
            }

            await Task.Delay(_workerConfig.DelayInSeconds, stoppingToken);
        }
    }
}

this class calls that and i think i know what's the problem, since EmailWorker class isn't injected, it uses the same IEmailSender thus it doesn't create new one right? @cap5lut

cap5lut•8mo ago

sorry was quick smoking yep thats it transient basically means its as long alive as the service u inject it into and background services are singletons if u would have injected the EmailSender directly into the controller u would have observed that _cachedHtml is always null because controllers are by default transient as well or if u would have injected the IServiceProvider and each time u want to use EmailSender u would request it again.

var es1 = serviceProvider.GetRequiredService<EmailSender>();
var es2 = serviceProvider.GetRequiredService<EmailSender>();
Console.WriteLine(object.ReferenceEquals(es1, es2)); // prints false

var es1 = serviceProvider.GetRequiredService<EmailSender>();
var es2 = serviceProvider.GetRequiredService<EmailSender>();
Console.WriteLine(object.ReferenceEquals(es1, es2)); // prints false

DachiOP•8mo ago

sure thanks

cap5lut•8mo ago

if this answers ur question, please dont forget to $close the thread

MODiX•8mo ago

Use the /close command to mark a forum thread as answered

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✅ How Scope lifetime works