如何从web.config里获取connectionString的值

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首先在web.config里定义了连接字符串：

...

</connectionStrings>

...

</configuration>

在DAO文件夹下新建SqlDAO.cs类文件：

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

namespace Web.DAO
{
    public class SqlDAO
    {
        private SqlConnection m_conn = null;
        private SqlCommand m_SqlCommand = null;
        SqlTransaction m_SqlTransaction = null;

        public SqlDAO()
        {
            string connString = ConfigurationManager.ConnectionStrings["eoexmaConnectionString"].ConnectionString;
            m_conn = new SqlConnection(connString);
            m_SqlCommand = new SqlCommand();
            m_SqlCommand.Connection = m_conn;
            m_conn.Open();
        }

        public void BeginTrans()
        {
            m_SqlTransaction = m_conn.BeginTransaction();
        }

        public void CommitTrans()
        {
            m_SqlTransaction.Commit();
            m_SqlTransaction = null;
        }

        public void Rollback()
        {
            m_SqlTransaction.Rollback();
            m_SqlTransaction = null;
        }

        public void Open()
        {
            if (this.m_conn.State == ConnectionState.Closed)
            {
                m_conn.Open();
            }
        }

        public void Close()
        {
            m_conn.Close();
        }

        public int ExecuteNonQuery(string sql, CommandType commandType, string[] sqlParams, object[] values)
        {
            m_SqlCommand.CommandText = sql;
            m_SqlCommand.CommandType = commandType;
            m_SqlCommand.Transaction = m_SqlTransaction;
            m_SqlCommand.Parameters.Clear();
            for (int i = 0; i < sqlParams.Length; i++)
            {
                SqlParameter param = new SqlParameter(sqlParams[i], values[i]);
                m_SqlCommand.Parameters.Add(param);
            }
            return m_SqlCommand.ExecuteNonQuery();
        }

        public int ExecuteNonQuery(string sql)
        {
            m_SqlCommand.CommandText = sql;
            m_SqlCommand.CommandType = CommandType.Text;
            m_SqlCommand.Transaction = m_SqlTransaction;
            m_SqlCommand.Parameters.Clear();
            return m_SqlCommand.ExecuteNonQuery();
        }

        public DataSet ExecuteQuery(string sql, CommandType commandType, string[] sqlParams, Object[] values)
        {
            m_SqlCommand.CommandText = sql;
            m_SqlCommand.CommandType = commandType;
            m_SqlCommand.Transaction = m_SqlTransaction;
            m_SqlCommand.Parameters.Clear();
            for (int i = 0; i < sqlParams.Length; i++)
            {
                SqlParameter param = new SqlParameter(sqlParams[i], values[i]);
                m_SqlCommand.Parameters.Add(param);
            }
            SqlDataAdapter sda = new SqlDataAdapter(m_SqlCommand);
            DataSet ds = new DataSet();
            sda.Fill(ds);
            return ds;
        }

        public DataSet ExecuteQuery(string sql)
        {
            m_SqlCommand.CommandText = sql;
            m_SqlCommand.CommandType = CommandType.Text;
            m_SqlCommand.Transaction = m_SqlTransaction;
            m_SqlCommand.Parameters.Clear();
            SqlDataAdapter sda = new SqlDataAdapter(m_SqlCommand);
            DataSet ds = new DataSet();
            sda.Fill(ds);
            return ds;
        }
    }
}

在Default.aspx.cs里使用：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace Web
{
    public partial class _Default : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            if (!IsPostBack)
            {
                this.GridView1.DataSource = new DAO.MYDAO().getAllInfo();
                this.GridView1.DataBind();
            }
        }
    }
}

即可。