public class CustomMaxLengthConvention : Convention
    {
        public CustomMaxLengthConvention()
        {
            this.Properties<string>().Configure(p => p.HasMaxLength(450));
        }
    }

    protected override void OnModelCreating(DbModelBuilder modelBuilder)
    {
       modelBuilder.Conventions.AddAfter<MaxLengthAttributeConvention>(new CustomMaxLengthConvention());

function addToken(data) {
   data.__RequestVerificationToken = $("input[name=__RequestVerificationToken]").val();
   return data;
}
 
$.ajax({
   // .....
   data: addToken({ postId: postId }), // اضافه کردن توکن
   dataType: "html", // نوع داده مهم است
   // .....
});