Question

Is it possible to modify the connectionstrings defined in the app.config/web.config at runtime? I want to use different configfiles depending on the machine the app/site is run on (only for debugging purposes, of course. We’ll use the regular config files when deployed).

I can write AppSettings, but not ConnectionStrings (AFAIK). Or can I?

Answer 1

Yes it’s possible, but AFAIK only via Reflection. The following code should do what you need (read below for usage):

public static string SetConnectionString(Type assemblyMember,                                          Type settingsClass,                                          string newConnectionString,                                          string connectionStringKey) {   Type typSettings = Type.GetType(Assembly.CreateQualifiedName(assemblyMember.Assembly.FullName, settingsClass.FullName));    if (typSettings == null)   {     return null;   }    PropertyInfo prpDefault = typSettings.GetProperty('Default', BindingFlags.Static | BindingFlags.Public);    if (prpDefault == null)   {     return null;   }    object objSettings = prpDefault.GetValue(null, null);    if (objSettings == null)   {     return null;   }    // the default property, this[], is actually named Item   PropertyInfo prpItem = objSettings.GetType().GetProperty('Item', BindingFlags.Instance | BindingFlags.Public);    if (prpItem == null)   {     return null;   }    object[] indexerName = { connectionStringKey };   string oldConnectionString = (string)prpItem.GetValue(objSettings, indexerName);    prpItem.SetValue(objSettings, newConnectionString, indexerName);    return oldConnectionString; } 

assemblyMember is the calling type
settingsClass is the type of your settings class
newConnectionString is the full string to set
connectionStringKey is the name of the connection string that you defined in your app’s settings

You should call this method as soon as possible after your app has started, preferably in the Main() method.