怎么样在ASP.NET中配置各种连接数据库？

 <connectionStrings>
 <add name="Conn" connectionString="server=.;database=demo;uid=sa;pwd=123456" providerName="System.Data.SqlClient"/>
 </connectionStrings> 

 <connectionStrings>
 <add name="Conn" connectionString="Provider=Microsoft.Jet.OLEDB.4.0; Data Source={0}App_Data/demo.mdb" providerName="System.Data.OleDb"/>
 </connectionStrings> 

 <connectionStrings>
 <add name="Conn" connectionString="Provider=Microsoft.Jet.OLEDB.4.0; Data Source={0}App_Data/demo.mdb" providerName="System.Data.OleDb"/>
 </connectionStrings> 

 <connectionStrings>
 <add name="Conn" connectionString="Provider=MSDAORA;Data Source=demo;User ID=sa;Password=123456;" providerName="System.Data.OracleClient"/>
 </connectionStrings> 

 <connectionStrings>
 <add name="Conn" connectionString="Data Source={0}App_Data/demo.db;failifmissing=false" providerName="System.Data.SQLite"/>
 </connectionStrings> 

 <connectionStrings>
 <add name="Conn" connectionString="host=127.0.0.1;Port=3306;Database=mysql;uid=sa;pwd=12346" providerName="MySql.Data.MySqlClient"/>
 </connectionStrings> 

using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Reflection;
using System.Text;
using System.Web;
using System.Web.Script.Serialization;

namespace Role.DAL
{
 public class Json
 {
 public Json() { }

 /// <summary>
 ///将datatable数据转换成JSON数据, 字符串拼接写成的
 /// </summary>
 /// <param name="jsonName">json名称。没发现什么作用</param>
 /// <param name="dt">得到的数据表</param>
 /// <returns></returns>
 public string DataTableToJson(string jsonName, DataTable dt)
 {
  StringBuilder Json = new StringBuilder();
  Json.Append("[");
  if (dt.Rows.Count > 0)
  {
  for (int i = 0; i < dt.Rows.Count; i++)
  {
   Json.Append("{");
   for (int j = 0; j < dt.Columns.Count; j++)
   {
   Json.Append(dt.Columns[j].ColumnName.ToString() + ":\"" + dt.Rows[i][j].ToString() + "\"");
   if (j < dt.Columns.Count - 1)
   {
    Json.Append(",");
   }
   }
   Json.Append("}");
   if (i < dt.Rows.Count - 1)
   {
   Json.Append(",");
   }
  }
  }
  Json.Append("]");
  return Json.ToString();
 }


 /// <summary>
 /// 列表数据转换到json数据;字符串拼接写成的，太难
 /// </summary>
 /// <typeparam name="T"></typeparam>
 /// <param name="jsonName">json名称。没发现什么作用</param>
 /// <param name="IL"></param>
 /// <returns></returns>
 public string ObjectToJson<T>(string jsonName, IList<T> IL)
 {
  StringBuilder Json = new StringBuilder();
  Json.Append("[");
  if (IL.Count > 0)
  {
  for (int i = 0; i < IL.Count; i++)
  {
   T obj = Activator.CreateInstance<T>();
   Type type = obj.GetType();
   PropertyInfo[] pis = type.GetProperties();
   Json.Append("{");
   for (int j = 0; j < pis.Length; j++)
   {
   Json.Append(pis[j].Name.ToString() + ":\"" + pis[j].GetValue(IL[i], null) + "\"");
   if (j < pis.Length - 1)
   {
    Json.Append(",");
   }
   }
   Json.Append("}");
   if (i < IL.Count - 1)
   {
   Json.Append(",");
   }
  }
  }
  Json.Append("]");
  return Json.ToString();
 }

 /// <summary>
 /// 将DataTable转化为自定义JSON数据
 /// </summary>
 /// <param name="dt">数据表</param>
 /// <returns>JSON字符串</returns> 
 public static string DataTableToJson(DataTable dt)
 {
  StringBuilder JsonString = new StringBuilder();
  if (dt != null && dt.Rows.Count > 0)
  {
  List<Dictionary<string, string>> list = new List<Dictionary<string, string>>();
  for (int i = 0; i < dt.Rows.Count; i++)
  {
   Dictionary<string, string> dict = new Dictionary<string, string>();
   for (int j = 0; j < dt.Columns.Count; j++)
   {
   dict.Add(dt.Columns[j].ColumnName, dt.Rows[i][j].ToString());
   }
   list.Add(dict);
  }
  JavaScriptSerializer jsonSerializer = new JavaScriptSerializer();
  return jsonSerializer.Serialize(list);
  }
  else
  {
  return "{}";
  }
 }

 /// <summary>
 /// 将datatable转换为json 
 /// </summary>
 /// <param name="dtb">Dt</param>
 /// <returns>JSON字符串</returns>
 public static string Dtb2Json(DataTable dtb)
 {
  JavaScriptSerializer jss = new JavaScriptSerializer();
  System.Collections.ArrayList dic = new System.Collections.ArrayList();
  if (dtb != null && dtb.Rows.Count > 0)
  {
  foreach (DataRow dr in dtb.Rows)
  {
   System.Collections.Generic.Dictionary<string, object> drow = new System.Collections.Generic.Dictionary<string, object>();
   foreach (DataColumn dc in dtb.Columns)
   {
   drow.Add(dc.ColumnName, dr[dc.ColumnName]);
   }
   dic.Add(drow);
  }
  //序列化 
  return jss.Serialize(dic);
  }
  else
  {
  return "{}";
  }
 }

 }
}