因此，我試圖從數(shù)據(jù)庫(kù)中獲取“客戶”，但出現(xiàn)異常System.Data.dll中發(fā)生類型'System.Data.SqlClient.SqlException'的異常，但未在用戶代碼中處理附加信息：必須聲明標(biāo)量變量"@Id"。    using Core;    using System;    using System.Collections.Generic;    using System.Configuration;    using System.Data.SqlClient;    using System.Linq;    using System.Text;    using System.Threading.Tasks;    namespace DatabaseAccess    {        public class DbCustomer        {            private string ConnectionString = ConfigurationManager.ConnectionStrings["local"].ConnectionString;            private SqlConnection connection { get; set; }            public DbCustomer()            {                connection = new SqlConnection(ConnectionString);            }            public Customer GetCustomer(int Id)            {                Customer customer = null;                connection.Open();                using (SqlCommand command = connection.CreateCommand())                {                    command.CommandText = "SELECT * FROM CUSTOMER WHERE Id = @Id;";                    var reader = command.ExecuteReader();                    while (reader.Read())                    {                        customer = new Customer();                        customer.Id = reader.GetInt32(reader.GetOrdinal("Id"));                        customer.FirstName = reader.GetString(reader.GetOrdinal("FirstName"));                        customer.LastName = reader.GetString(reader.GetOrdinal("LastName"));                        customer.Address = reader.GetString(reader.GetOrdinal("Address"));                    }                    command.ExecuteNonQuery();                    connection.Close();                }                return customer;            }        }    }using System;using System.Collections.Generic;using System.Linq;using System.Runtime.Serialization;using System.Text;using System.Threading.Tasks;