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Added CRonBackgroundWorker example
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‎CronBackgroundWorker/AnotherCronJob.cs

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using CronBackgroundWorker.Cron;
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namespace CronBackgroundWorker;
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public class AnotherCronJob : ICronJob
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{
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public Task Run(CancellationToken token = default)
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{
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Console.WriteLine($"Hello from {nameof(AnotherCronJob)} at: {DateTime.UtcNow.ToShortTimeString()}");
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return Task.CompletedTask;
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}
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}

‎CronBackgroundWorker/Cron/CronJobExtensions.cs

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using Microsoft.Extensions.DependencyInjection.Extensions;
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using NCrontab;
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namespace CronBackgroundWorker.Cron;
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public static class CronJobExtensions
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{
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public static IServiceCollection AddCronJob<T>(this IServiceCollection services, string cronExpression)
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where T : class, ICronJob
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{
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var cron = CrontabSchedule.TryParse(cronExpression)
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?? throw new ArgumentException("Invalid cron expression", nameof(cronExpression));
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var entry = new CronRegistryEntry(typeof(T), cron);
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// AddHostedService internally only registers one time
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services.AddHostedService<CronScheduler>();
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// TryAdd prevents multiple registrations of T
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services.TryAddSingleton<T>();
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services.AddSingleton(entry);
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return services;
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}
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}

‎CronBackgroundWorker/Cron/CronRegistryEntry.cs

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using NCrontab;
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namespace CronBackgroundWorker.Cron;
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public sealed record CronRegistryEntry(Type Type, CrontabSchedule CrontabSchedule);

‎CronBackgroundWorker/Cron/CronScheduler.cs

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namespace CronBackgroundWorker.Cron;
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public sealed class CronScheduler : BackgroundService
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{
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private readonly IServiceProvider _serviceProvider;
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private readonly IReadOnlyCollection<CronRegistryEntry> _cronJobs;
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public CronScheduler(
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IServiceProvider serviceProvider,
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IEnumerable<CronRegistryEntry> cronJobs)
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{
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// Use the container
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_serviceProvider = serviceProvider;
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_cronJobs = cronJobs.ToList();
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}
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protected override async Task ExecuteAsync(CancellationToken stoppingToken)
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{
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// Create a timer that has a resolution less than 60 seconds
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// Because cron has a resolution of a minute
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// So everything under will work
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using var tickTimer = new PeriodicTimer(TimeSpan.FromSeconds(30));
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// Create a map of the next upcoming entries
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var runMap = new Dictionary<DateTime, List<Type>>();
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while (await tickTimer.WaitForNextTickAsync(stoppingToken))
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{
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// Get UTC Now with minute resolution (remove microseconds and seconds)
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var now = UtcNowMinutePrecision();
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// Run jobs that are in the map
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RunActiveJobs(runMap, now, stoppingToken);
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// Get the next run for the upcoming tick
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runMap = GetJobRuns();
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}
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}
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private void RunActiveJobs(IReadOnlyDictionary<DateTime, List<Type>> runMap, DateTime now, CancellationToken stoppingToken)
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{
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if (!runMap.TryGetValue(now, out var currentRuns))
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{
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return;
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}
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foreach (var run in currentRuns)
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{
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// We are sure (thanks to our extension method)
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// that the service is of type ICronJob
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var job = (ICronJob)_serviceProvider.GetRequiredService(run);
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// We don't want to await jobs explicitly because that
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// could interfere with other job runs
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job.Run(stoppingToken);
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}
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}
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private Dictionary<DateTime, List<Type>> GetJobRuns()
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{
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var runMap = new Dictionary<DateTime, List<Type>>();
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foreach (var cron in _cronJobs)
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{
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var utcNow = DateTime.UtcNow;
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var runDates = cron.CrontabSchedule.GetNextOccurrences(utcNow, utcNow.AddMinutes(1));
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if (runDates is not null)
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{
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AddJobRuns(runMap, runDates, cron);
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}
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}
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return runMap;
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}
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private static void AddJobRuns(IDictionary<DateTime, List<Type>> runMap, IEnumerable<DateTime> runDates, CronRegistryEntry cron)
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{
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foreach (var runDate in runDates)
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{
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if (runMap.TryGetValue(runDate, out var value))
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{
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value.Add(cron.Type);
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}
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else
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{
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runMap[runDate] = new List<Type> { cron.Type };
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}
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}
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}
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private static DateTime UtcNowMinutePrecision()
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{
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var now = DateTime.UtcNow;
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return new DateTime(now.Year, now.Month, now.Day, now.Hour, now.Minute, 0);
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}
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}

‎CronBackgroundWorker/Cron/ICronJob.cs

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namespace CronBackgroundWorker.Cron;
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public interface ICronJob
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{
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Task Run(CancellationToken token = default);
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}

‎CronBackgroundWorker/CronBackgroundWorker.csproj

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<Project Sdk="Microsoft.NET.Sdk.Web">
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<PropertyGroup>
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<TargetFramework>net7.0</TargetFramework>
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<Nullable>enable</Nullable>
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<ImplicitUsings>enable</ImplicitUsings>
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</PropertyGroup>
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<ItemGroup>
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<PackageReference Include="NCrontab" Version="3.3.1" />
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</ItemGroup>
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</Project>

‎CronBackgroundWorker/CronBackgroundWorker.sln

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Microsoft Visual Studio Solution File, Format Version 12.00
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Project("{FAE04EC0-301F-11D3-BF4B-00C04F79EFBC}") = "CronBackgroundWorker", "CronBackgroundWorker.csproj", "{DDB36A76-DBB7-47DC-8702-F4F36019193E}"
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EndProject
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Global
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GlobalSection(SolutionConfigurationPlatforms) = preSolution
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Debug|Any CPU = Debug|Any CPU
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Release|Any CPU = Release|Any CPU
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EndGlobalSection
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GlobalSection(ProjectConfigurationPlatforms) = postSolution
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{DDB36A76-DBB7-47DC-8702-F4F36019193E}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
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{DDB36A76-DBB7-47DC-8702-F4F36019193E}.Debug|Any CPU.Build.0 = Debug|Any CPU
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{DDB36A76-DBB7-47DC-8702-F4F36019193E}.Release|Any CPU.ActiveCfg = Release|Any CPU
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{DDB36A76-DBB7-47DC-8702-F4F36019193E}.Release|Any CPU.Build.0 = Release|Any CPU
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EndGlobalSection
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EndGlobal

‎CronBackgroundWorker/CronJob.cs

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using CronBackgroundWorker.Cron;
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namespace CronBackgroundWorker;
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public class CronJob : ICronJob
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{
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private readonly ILogger<CronJob> _logger;
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public CronJob(ILogger<CronJob> logger)
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{
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_logger = logger;
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}
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public Task Run(CancellationToken token = default)
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{
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_logger.LogInformation("Hello from {name} at: {time}", nameof(CronJob), DateTime.UtcNow.ToShortTimeString());
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return Task.CompletedTask;
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}
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}

‎CronBackgroundWorker/Program.cs

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using CronBackgroundWorker;
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using CronBackgroundWorker.Cron;
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var builder = WebApplication.CreateBuilder(args);
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builder.Services.AddCronJob<CronJob>("* * * * *");
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builder.Services.AddCronJob<AnotherCronJob>("*/2 * * * *");
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var app = builder.Build();
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app.Run();

‎CronBackgroundWorker/Properties/launchSettings.json

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{
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"$schema": "https://json.schemastore.org/launchsettings.json",
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"iisSettings": {
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"windowsAuthentication": false,
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"anonymousAuthentication": true,
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"iisExpress": {
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"applicationUrl": "http://localhost:32380",
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"sslPort": 44343
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}
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},
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"profiles": {
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"http": {
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"commandName": "Project",
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"dotnetRunMessages": true,
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"launchBrowser": true,
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"launchUrl": "swagger",
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"applicationUrl": "http://localhost:5163",
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"environmentVariables": {
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"ASPNETCORE_ENVIRONMENT": "Development"
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}
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},
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"https": {
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"commandName": "Project",
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"dotnetRunMessages": true,
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"launchBrowser": true,
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"launchUrl": "swagger",
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"applicationUrl": "https://localhost:7250;http://localhost:5163",
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"environmentVariables": {
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"ASPNETCORE_ENVIRONMENT": "Development"
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}
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},
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"IIS Express": {
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"commandName": "IISExpress",
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"launchBrowser": true,
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"launchUrl": "swagger",
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"environmentVariables": {
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"ASPNETCORE_ENVIRONMENT": "Development"
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}
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}
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}
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}

‎CronBackgroundWorker/appsettings.json

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{
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"Logging": {
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"LogLevel": {
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"Default": "Information",
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"Microsoft.AspNetCore": "Warning"
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}
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},
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"AllowedHosts": "*"
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}

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