“T”必须是具有公共的无参数构造函数的非抽象类型，才能用作泛型类型或方法

public class BaseDal<T> where T:class
    {
        private readonly SqlSugarClient _db = SqlSugarFatory.GetInstance();

        #region 插入方法

        /// <summary>
        /// 插入并返回受影响行数用ExecuteCommand
        /// </summary>
        /// <param name="model"></param>
        /// <returns></returns>
        public int Add(T model)
        {
            //忽略该字段的插入
            _db.IgnoreColumns.Add("id", "t_sys_user");
            var result = _db.Insertable(model).ExecuteCommand();
            return result;
        }

public class BaseDal<T> where T:class,new()