ADO.Net 精简的三层架构（初学者）

DAL（Data Access Layer）

三层架构是企业开发中常用的设计模式，把数据库访问、业务逻辑、界面分离。

初学者直接学习三层架构比较难，因此先学习精简的三层架构，只用DAL层，把数据库访问封装到DAL中，UI调用DAL，原则“UI中不出现SQL”。

DAL常用封装：ToModel、ListAll、GetById、DeleteById、Update、Insert

下面是一个使用DAL的实例：

数据库表

T_Customer定义

代码清单：

配置文件：App.config

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <connectionStrings>
    <add name="myconnstr" connectionString="Data Source=.; Initial Catalog = ADOTest; User ID = sa; Password = 123456"/>
  </connectionStrings>
</configuration>

/Model：模型类

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ADOTest5.Model
{
    public class Customer
    {
        public long Id {get;set;}
        public string Name { get; set; }
        public DateTime? Birthday { get; set; }
        public string Address { get; set; }
        public string TelNum { get; set; }
        public int CustLevel { get; set; }
    }
}

/DAL/CustomerDAL.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using ADOTest5.Model;
using System.Data;
using System.Data.SqlClient;

namespace ADOTest5.DAL
{
    public  class CustomerDAL
    {
        //根据Id获取GetById、Update、DeleteById、GetAll、GetPagedData（分页数据）
        //Insert（插入新数据）

        //把公共的代码封装到一个方法中，这样可以避免重复性的代码，提高代码复用性
        private Customer ToCustomer(DataRow row)
        {
            Customer cust = new Customer();
            cust.Id = (int)row["Id"];
            cust.Name = (string)row["Name"];
            cust.Birthday = (DateTime?)SqlHelper.FromDbValue(row["Birthday"]);
            cust.Address = (string)row["Address"];
            cust.CustLevel = (int)row["CustLevel"];
            cust.TelNum = (string)row["TelNum"];
            return cust;
        }
        /// <summary>
        /// 根据Id查询结果
        /// </summary>
        /// <param name="id"></param>
        /// <returns></returns>
        public Customer GetById(long id)
        {
            DataTable dt = SqlHelper.ExecuteDataTable("select * from T_Customer where Id = @Id"
                ,new SqlParameter("@Id",id));
            if (dt.Rows.Count <= 0)
            {
                return null;
            }
            else if (dt.Rows.Count > 1)
            {
                throw new Exception("严重错误，查出多条数据！");
            }
            else
            {
                DataRow row = dt.Rows[0];
                return ToCustomer(row);
            }
        }

        /// <summary>
        /// 根据Id删除数据
        /// </summary>
        /// <param name="id"></param>
        public void DeleteById(long id)
        {
            SqlHelper.ExecuteNonQuery("delete from T_Customer where Id = @Id",
                new SqlParameter("@Id", id));

        }

        /// <summary>
        /// 往数据库中插入数据
        /// </summary>
        /// <param name="customer"></param>
        public void Insert(Customer customer)
        {
            SqlHelper.ExecuteNonQuery(@"Insert into T_Customer(Name,
                Birthday, Address, TelNum, CustLevel)
                values(@Name, @Birthday, @Address, @TelNum, @CustLevel)",
                new SqlParameter("@Name",customer.Name),
                new SqlParameter("@Birthday",SqlHelper.ToDbValue(customer.Birthday)),
                new SqlParameter("@Address", customer.Address),
                new SqlParameter("@TelNum", customer.TelNum),
                new SqlParameter("@CustLevel",customer.CustLevel));
        }

        /// <summary>
        /// 更新数据
        /// </summary>
        /// <param name="customer"></param>
        public void Update(Customer customer)
        {
            SqlHelper.ExecuteNonQuery(@"Update T_Customer set 
                    Name = @Name, Birthday = @Birthday, Address = @Address,
                    TelNum = @TelNum, CustLevel = @CustLevel 
                    where Id = @Id",
                    new SqlParameter("@Name", customer.Name),
                    new SqlParameter("@Birthday", SqlHelper.ToDbValue(customer.Birthday)),
                    new SqlParameter("@Address", customer.Address),
                    new SqlParameter("@TelNum", customer.TelNum),
                    new SqlParameter("@CustLevel", customer.CustLevel));
        }


        /// <summary>
        /// 查询所有数据
        /// </summary>
        /// <returns></returns>
        public Customer[] GetAll()
        {
            DataTable table = SqlHelper.ExecuteDataTable("select * from T_Customer");
            Customer[] customers = new Customer[table.Rows.Count];
            for (int i = 0; i < table.Rows.Count; i++)
            {
                DataRow row = table.Rows[i];
                customers[i] = ToCustomer(row);
            }
            return customers;
        }

    }
}

/DAL/SqlHelper.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Configuration;
using System.Data.SqlClient;
using System.Data;

namespace ADOTest5.DAL
{
    static class SqlHelper
    {
        public static readonly string connstr = ConfigurationManager.ConnectionStrings["myconnstr"].ConnectionString;

        public static int ExecuteNonQuery(string sql,
            params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(connstr))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = sql;
                    cmd.Parameters.AddRange(parameters);
                    return cmd.ExecuteNonQuery();
                }
            }
        }

        public static object ExecuteScalar(string sql,
            params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(connstr))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = sql;
                    cmd.Parameters.AddRange(parameters);
                    return cmd.ExecuteScalar();
                }
            }
        }


        public static DataTable ExecuteDataTable(string sql,
            params SqlParameter[] parameters)
        {
            using (SqlConnection conn = new SqlConnection(connstr))
            {
                conn.Open();
                using (SqlCommand cmd = conn.CreateCommand())
                {
                    cmd.CommandText = sql;
                    cmd.Parameters.AddRange(parameters);
                    DataSet ds = new DataSet();
                    SqlDataAdapter adapter = new SqlDataAdapter(cmd);
                    adapter.Fill(ds);
                    return ds.Tables[0];
                }
            }
        }

        public static object FromDbValue(object value)
        {
            if (value == DBNull.Value)
            {
                return null;
            }
            else
            {
                return value;
            }
        }

        public static object ToDbValue(object value)
        {
            if (value == null)
            {
                return DBNull.Value;
            }
            else
            {
                return value;
            }
        }
    }
}