public class ArticleService : IArticleService
{
        private readonly BlogDbContext db;
        private readonly IDateTimeProvider dateTimeProvider;

        public ArticleService(
            BlogDbContext db,
            IDateTimeProvider dateTimeProvider)
        {
            this.db = db;
            this.dateTimeProvider = dateTimeProvider;
        }

        public async Task<int> Add(string title, string content, string userId)
        {
            var article = new Article
            {
                Title = title,
                Content = content,
                UserId = userId,
                PublishedOn = this.dateTimeProvider.Now();
            };

            this.db.Articles.Add(article);

            await this.db.SaveChangesAsync();

            return article.Id;
        }
}