protected override void OnModelCreating(ModelBuilder modelBuilder)
        {
            base.OnModelCreating(modelBuilder);

            modelBuilder.Entity<UserRoleModel>()
                .HasKey(ur => new { ur.UserId, ur.RoleId });
            modelBuilder.Entity<UserRoleModel>()
                .HasOne(ur => ur.User)
                .WithMany(u => u.UserRoles)
                .HasForeignKey(ur => ur.UserId);
            modelBuilder.Entity<UserRoleModel>()
                .HasOne(ur => ur.Role)
                .WithMany(r => r.UserRoles)
                .HasForeignKey(ur => ur.RoleId);
        }