How do I set a connection string config programatically in .net?

Question

I'd like to set a connection string programmatically, with absolutely no change to any config files / registry keys.

I have this piece of code, but unfortunately it throws an exception with "the configuration is read only".

ConfigurationManager.ConnectionStrings.Clear();
string connectionString = "Server=myserver;Port=8080;Database=my_db;...";
ConnectionStringSettings connectionStringSettings = 
  new ConnectionStringSettings("MyConnectionStringKey", connectionString);
ConfigurationManager.ConnectionStrings.Add(connectionStringSettings);

Edit: The problem is that I have existing code that reads the connection string from the configuration. So setting the config string manually, or through a resource, don't seem like valid options. What I really need is a way to modify the configuration programmatically.

Answer 1

You could put it in a resources file instead. It won't have the built-in features of the ConfigurationManager class, but it will work.

Assuming Resources.resx:

Resources.Default.ConnectionString = "Server=myserver;" // etc

Then in your code:

conn.ConnectionString = Resources.Default.ConnectionString

It's a hack, I know.

Answer 2

ConfigurationManager is used to read from the config file.

Your solution is to simply set conn.ConnectionString to the conn string you need.

Answer 3

I'm currently using dependency injection to handle different connection strings in dev/prod vs. test environments. I still have to manually change the webconfig if I want to move to between dev and prod, but for testing I have an IConnectionStringFactory interface with a default implementation that looks at the web config and an alternate testing configuration that returns static values. That way when I'm testing I simply set the factory to the testing implementation and it will return the testing connection string for the key I ask for. Otherwise it will look in the webconfig.

I could extend this to another implementation for dev vs. prod but I'm more comfortable having a single implementation of IConnectionStringFactory in my production assembly and the testing implementation in my testing assembly.

Answer 4

In addition to the other answers given, and assuming the connection string is not simply another configuration variable or constant as a whole, you might consider using SqlConnectionString class instead of directly concatenating the string together.

EDIT: Ups, sorry just saw that you basically want to read your connection string (complete I guess) from another source.

Answer 5

I've written about this in a post on my blog. The trick is to use reflection to poke values in as a way to get access to the non-public fields (and methods).

eg.

var settings = ConfigurationManager.ConnectionStrings[ 0 ];

var fi = typeof( ConfigurationElement ).GetField( "_bReadOnly", BindingFlags.Instance | BindingFlags.NonPublic );

fi.SetValue(settings, false);

settings.ConnectionString = "Data Source=Something";

Answer 6

I find that this works for me:

Configuration config = WebConfigurationManager.OpenWebConfiguration("~");
ConnectionStringsSection section = config.GetSection("connectionStrings") as         ConnectionStringsSection;
if (section != null)
{
    section.ConnectionStrings["MyConnectionString"].ConnectionString = connectionString;
    config.Save();
}

This overwrites an existing connection string.

Answer 7

sorry - answer linked from another forum for a different purpose. Didn't read entire thread before updating here...