C# 委托

  public T Query<T>(int id) where T : BaseModel
        {
            Type type = typeof(T);
            string columnString = string.Join(",", type.GetProperties().Select(p => $"[{p.GetColumnName()}]"));
            string sql = $"SELECT {columnString} FROM [{type.Name}] WHERE Id=@Id";
            T t = default(T);
            DataTable dt = new DataTable();

            Func<SqlCommand, T> func = (SqlCommand command) =>//1 将要执行的先准备好
            {
                SqlParameter para = new SqlParameter("@Id", id);//3 func.invoke(command) 执行这里并返回
                command.Parameters.Add(para);
                SqlDataAdapter adapter = new SqlDataAdapter(command);
                //SqlDataReader reader = command.ExecuteReader();
                //List<T> list = this.ReaderToList<T>(reader);
                adapter.Fill(dt);
                List<T> list = ConvertToList<T>(dt);
                T tResult = list.FirstOrDefault();
                return tResult;
            };
            t = ExcuteSql<T>(sql, func);
            return t;
        }

 private T ExcuteSql<T>(string sql, Func<SqlCommand, T> func)
        {
            using (SqlConnection conn = new SqlConnection(strConn))
            {
                using (SqlCommand command = new SqlCommand(sql, conn))
                {
                    conn.Open();
                    SqlTransaction sqlTransaction = conn.BeginTransaction();
                    try
                    {
                        command.Transaction = sqlTransaction;
                        T tResult = func.Invoke(command);//2执行前面准备好的。
                        sqlTransaction.Commit();
                        return tResult;
                    }
                    catch (Exception ex)
                    {
                        sqlTransaction.Rollback();
                        throw;
                    }
                }
            }
        }