网上购物系统（Task004）——通用数据库访问函数

源代码：13033480群共享

一、try…catch…finally结构

using System;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Collections.Generic;
using WestGarden.Model;

namespace WestGarden.Web
{
    public partial class Default1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            IList<CategoryInfo> catogories = new List<CategoryInfo>();

            string connectionString = ConfigurationManager.ConnectionStrings["NetShopConnString"].ConnectionString;
            string cmdText = "SELECT * FROM Category";

            SqlCommand cmd = new SqlCommand();

            SqlConnection conn = new SqlConnection(connectionString);

            try
            {
                cmd.Connection = conn;
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = cmdText;

                conn.Open();

                SqlDataReader rdr = cmd.ExecuteReader();
                while (rdr.Read())
                {
                    CategoryInfo category = new CategoryInfo(rdr.GetString(0), rdr.GetString(1), rdr.GetString(2));
                    catogories.Add(category);
                }
                rdr.Close();
            }
            finally
            {
                conn.Close();
            }

            ddlCategories.DataSource = catogories;
            ddlCategories.DataTextField = "Name";
            ddlCategories.DataValueField = "CategoryId";
            ddlCategories.DataBind();
        }
    }
}

二、using()结构

using System;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Collections.Generic;
using WestGarden.Model;

namespace WestGarden.Web
{
    public partial class Default2 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            IList<CategoryInfo> catogories = new List<CategoryInfo>();

            string connectionString = ConfigurationManager.ConnectionStrings["NetShopConnString"].ConnectionString;
            string cmdText = "SELECT * FROM Category";

            SqlCommand cmd = new SqlCommand();

            //简单地说，using()结构等同于前面的try...finally结构，隐式关闭了conn。
            using(SqlConnection conn = new SqlConnection(connectionString))
            {
                cmd.Connection = conn;
                cmd.CommandType = CommandType.Text;
                cmd.CommandText = cmdText;

                conn.Open();

                SqlDataReader rdr = cmd.ExecuteReader();
                while (rdr.Read())
                {
                    CategoryInfo category = new CategoryInfo(rdr.GetString(0), rdr.GetString(1), rdr.GetString(2));
                    catogories.Add(category);
                }
                rdr.Close();
            }

            ddlCategories.DataSource = catogories;
            ddlCategories.DataTextField = "Name";
            ddlCategories.DataValueField = "CategoryId";
            ddlCategories.DataBind();
        }
    }
}

三、通用的数据库访问函数

using System;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Collections.Generic;
using WestGarden.Model;

namespace WestGarden.Web
{
    public partial class Default3 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            IList<CategoryInfo> catogories = new List<CategoryInfo>();

            string connectionString = ConfigurationManager.ConnectionStrings["NetShopConnString"].ConnectionString;
            string cmdText = "SELECT * FROM Category";

            SqlDataReader rdr = ExecuteReader(connectionString, CommandType.Text, cmdText);

            while (rdr.Read())
            {
                CategoryInfo category = new CategoryInfo(rdr.GetString(0), rdr.GetString(1), rdr.GetString(2));
                catogories.Add(category);
            }
            rdr.Close();

            ddlCategories.DataSource = catogories;
            ddlCategories.DataTextField = "Name";
            ddlCategories.DataValueField = "CategoryId";
            ddlCategories.DataBind();
        }

        public static SqlDataReader ExecuteReader(string connectionString, CommandType cmdType, string cmdText)
        {
            SqlCommand cmd = new SqlCommand();

            SqlConnection conn = new SqlConnection(connectionString);

            try
            {
                cmd.Connection = conn;
                cmd.CommandType = cmdType;
                cmd.CommandText = cmdText;

                conn.Open();
                
                //如果创建了 SqlDataReader 并将 CommandBehavior 设置为 CloseConnection，
                //则关闭 SqlDataReader 会自动关闭此连接
                SqlDataReader rdr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                return rdr;
            }
            catch
            {
                conn.Close();
                throw;
            }
            //finally
            //{
            //    conn.Close();
            //}
        }
    }
}

四、完善一下通用数据库访问函数

using System;
using System.Data;
using System.Data.SqlClient;
using System.Configuration;
using System.Collections.Generic;
using WestGarden.Model;

namespace WestGarden.Web
{
    public partial class Default4 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            IList<CategoryInfo> catogories = new List<CategoryInfo>();

            string connectionString = ConfigurationManager.ConnectionStrings["NetShopConnString"].ConnectionString;
            string cmdText = "SELECT * FROM Category";

            SqlDataReader rdr = ExecuteReader(connectionString, CommandType.Text, cmdText,null);

            while (rdr.Read())
            {
                CategoryInfo category = new CategoryInfo(rdr.GetString(0), rdr.GetString(1), rdr.GetString(2));
                catogories.Add(category);
            }
            rdr.Close();

            ddlCategories.DataSource = catogories;
            ddlCategories.DataTextField = "Name";
            ddlCategories.DataValueField = "CategoryId";
            ddlCategories.DataBind();
        }

        public static SqlDataReader ExecuteReader(string connectionString, CommandType cmdType, string cmdText, params SqlParameter[] commandParameters)
        {
            SqlCommand cmd = new SqlCommand();
            SqlConnection conn = new SqlConnection(connectionString);

            try
            {
                //cmd.Connection = conn;
                //cmd.CommandType = cmdType;
                //cmd.CommandText = cmdText;
                
                //conn.Open();

                PrepareCommand(cmd, conn, null, cmdType, cmdText, commandParameters);

                //如果创建了 SqlDataReader 并将 CommandBehavior 设置为 CloseConnection，
                //则关闭 SqlDataReader 会自动关闭此连接。
                SqlDataReader rdr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
                cmd.Parameters.Clear();
                return rdr;
            }
            catch
            {
                conn.Close();
                throw;
            }
            //finally
            //{
            //    conn.Close();
            //}
        }

        private static void PrepareCommand(SqlCommand cmd, SqlConnection conn, SqlTransaction trans, CommandType cmdType, string cmdText, SqlParameter[] cmdParms)
        {

            if (conn.State != ConnectionState.Open)
                conn.Open();

            cmd.Connection = conn;
            cmd.CommandText = cmdText;

            if (trans != null)
                cmd.Transaction = trans;

            cmd.CommandType = cmdType;

            if (cmdParms != null)
            {
                foreach (SqlParameter parm in cmdParms)
                    cmd.Parameters.Add(parm);
            }
        }
    }
}

五、使用Reapter显示分类名称

1、窗体代码：

<asp:Repeater ID="repCategories" runat="server">
    <HeaderTemplate>
        <table cellspacing="0" border="0" style="border-collapse: collapse;">
    </HeaderTemplate>
    <ItemTemplate>
        <tr>
            <td>
                <asp:HyperLink runat="server" ID="lnkCategory" NavigateUrl='<%# string.Format("~/Items.aspx?page=0&categoryId={0}", Eval("CategoryId")) %>'
                    Text='<%# Eval("Name") %>' /><asp:HiddenField runat="server" ID="hidCategoryId" Value='<%# Eval("CategoryId") %>' />
            </td>
        </tr>
    </ItemTemplate>
    <FooterTemplate>
        </table>
    </FooterTemplate>
</asp:Repeater>

2、代码页绑定代码：

repCategories.DataSource = catogories;
repCategories.DataBind();

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