private static void CreateDbIfNotExists(IWebHost host)
        {
            using (var scope = host.Services.CreateScope())
            {
                var services = scope.ServiceProvider;
                try
                {
                    var context = services.GetRequiredService<MediaContext>();
                    context.Database.EnsureCreated();
                }
                catch (Exception ex)
                {
                    var logger = services.GetRequiredService<ILogger<Program>>();
                    logger.LogError(ex, "An error occurred creating the DB.");
                }
            }
        }


        //MediaContext:DbContext
        //省略其他，重写创建模型方法
        protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            //映射创建表，如果表已经存在就不会再创建。
            modelBuilder.Entity<User>().ToTable("Tbl_User");
            modelBuilder.Entity<Attachment>().ToTable("Tbl_Attachment");
            modelBuilder.Entity<Role>().ToTable("Tbl_Role");
            modelBuilder.Entity<AlbumDetail>().ToTable("Tbl_AlbumDetail");
            modelBuilder.Entity<Album>().ToTable("Tbl_Album");
            modelBuilder.Entity<AlbumDetailModel>().ToView("V_AlbumDetail");
            modelBuilder.Entity<AlbumModel>().ToView("V_Album");
            try
            {
                //视图不能直接映射创建，所以这里直接用SQL语句来创建
                Database.ExecuteSqlRaw("CREATE VIEW \"V_Album\" AS select album.*,att.RemoteDomain,att.RelativePath from Tbl_Album album left join Tbl_Attachment att on album.ThumbnailId = att.Id WHERE NOT EXISTS (SELECT * FROM sqlite_master s WHERE s.type = 'view' AND name = 'V_Album')");

                Database.ExecuteSqlRaw("CREATE VIEW \"V_AlbumDetail\" AS select ad.*,( fa.RemoteDomain||'/' ||fa.RelativePath ) as Url, (ta.RemoteDomain||'/' ||ta.RelativePath ) as Thumbnail from Tbl_AlbumDetail ad inner join Tbl_Attachment fa on ad.AttachmentId=fa.Id inner join Tbl_Attachment ta on ad.ThumbnailId =ta.Id WHERE NOT EXISTS (SELECT * FROM sqlite_master s WHERE s.type = 'view' AND name = 'V_AlbumDetail')");

            }
            catch
            {

            }
        }