how to change to connection string in web.config dynamically

I defind the conne开发者_Python百科ction string in web.config

     <ConnectionStrings>
 <add name="student" connectionString="Server=student;Max Pool Size=300;Initial Catalog=studentDB;User ID=student;Password=st123dent;" providerName="System.Data.SqlClient"/>
     </Connectionstrings>

how can i change the connection string dynamically in c#

Configuration is read only so you can not do it in obvious way like

ConfigurationManager.ConnectionStrings["student"].ConnectionString = "new value";

This raises System.Configuration.ConfigurationErrorsException exception which saying that "Configuration is read only".

Here is a trick using reflection to reset readOnly attribute of configuration element. See this article for full details Programmatically setting a connectionString property

Code snippet:

var settings = ConfigurationManager.ConnectionStrings[ 0 ];
var fi = typeof(ConfigurationElement).GetField(
              "_bReadOnly", 
              BindingFlags.Instance | BindingFlags.NonPublic);
fi.SetValue(settings, false);
settings.ConnectionString = "Data Source=Something";

BTW, why you need change it the configuration? I'm feeling that you'are trying to solve some problem in wrong way.

You can open your Web.Config file for reading and writing using WebConfigurationManager.OpenWebConfiguration or WebConfigurationManager.OpenMappedWebConfiguration. And provided you have write permission you'll be able to make modifications such as changing the connection string.

This surely has to be better than using reflection to modify a private field.

Modifying web.config will then recycle the web application, so this isn't suitable for letting users make changes to web.config - though it could be used in specific scenarios such as deployment.

Example:

var configurationFileInfo = new FileInfo(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);
var vdm = new VirtualDirectoryMapping(configurationFileInfo.DirectoryName, true, configurationFileInfo.Name);
var wcfm = new WebConfigurationFileMap();
wcfm.VirtualDirectories.Add("/", vdm);
Configuration config = WebConfigurationManager.OpenMappedWebConfiguration(wcfm, "/");

ConnectionStringsSection section = config.GetSection("connectionStrings") 
                         as ConnectionStringsSection;
if (section != null)
{
    ... modify the section ...
    config.Save();
}

in Web Confige put this code

<add name="yourconnectionname" connectionString="Data Source={0};Initial Catalog={1};User ID={2};Password={3}" providerName="System.Data.SqlClient"/>

in your connection put this code

 string ScrtCon = ConfigurationManager.ConnectionStrings["yourconnectionname"].ToString();
ScrtCon = string.Format(ScrtCon, "Server Name","Data base Name",  "Database User Name", "Database password");

If a user is able to change the value of the Setting, then the web.config file is the wrong place to store the setting.

You should check out a User Scoped value in a Settings file instead.

MSDN - Using Settings in C

When using settings like this, changing the value at runtime is easy:

Properties.Settings.Default.ConnectionStringName = "New Connection String";
Properties.Settings.Default.Save();

Use NameSpace

using System.Configuration;
using System.Web.Configuration;


void ConfigurnewConnectionString(string server, string database, string userid, string password)
    {


    string str = "server=" + server + ";database=" + database + "; User ID=" + userid + "; Password=" + password + "";
    //Configuration myConfiguration = System.Web.Configuration.WebConfigurationManager.OpenWebConfiguration("~");
    //str = System.Web.Configuration.WebConfigurationManager.AppSettings["myKey"];
    //myConfiguration.Save();
    System.Configuration.Configuration Config1 = WebConfigurationManager.OpenWebConfiguration("~");
    ConnectionStringsSection conSetting = (ConnectionStringsSection)Config1.GetSection("connectionStrings");
    ConnectionStringSettings StringSettings = new ConnectionStringSettings("conn", "Data Source=" + server + ";Database=" + database + ";User ID=" + userid + ";Password=" + password + ";");
    conSetting.ConnectionStrings.Remove(StringSettings);
    conSetting.ConnectionStrings.Add(StringSettings);
    Config1.Save(ConfigurationSaveMode.Modified);
    //Configuration myConfiguration = System.Web.Configuration.WebConfigurationManager.OpenWebConfiguration("~");
    //myConfiguration.AppSettings.Settings.Item("myKey").Value = txtmyKey.Text;
    //myConfiguration.Save();
}