ApplicationStartedHandler.cs

namespace Morodar.TS3.Service.Handlers.Notification
{
    // Code simplified for demonstration
    public class ApplicationStartedHandler : INotificationHandler<ApplicationStartedNotification>
    {
        private readonly IRepository<ServerConfig> serverConfigRepository;
        private readonly ITeamSpeakClientRepository teamSpeakClientRepository;

        public ApplicationStartedHandler(
            IRepository<ServerConfig> serverConfigRepository,
            ITeamSpeakClientRepository teamSpeakClientRepository)
        {
            this.serverConfigRepository = serverConfigRepository;
            this.teamSpeakClientRepository = teamSpeakClientRepository;
        }
        public async Task Handle(
            ApplicationStartedNotification notification, 
            CancellationToken cancellationToken)
        {
            var allConfigs = await serverConfigRepository.GetAllAsync();     
            await Task.WhenAll(
                allConfigs.Select(
                    config => teamSpeakClientRepository.CreateClientAsync(config)));
        }
    }
}