ADO.NET |DataDirectory| where is this documented?

Question

In AppConfig it is possible to use |DataDirectory| but I can't find any doc ?

Answer 1

|DataDirectory| is a substitution string so you can configure the location of your database file separately.

So instead of:

SqlConnection c = new SqlConnection (    @"Data Source=.\SQLDB; AttachDbFilename=C:\MyDB\Database.mdf;Initial Catalog=Master"); 

you do the following:

// Set |DataDirectory| value AppDomain.CurrentDomain.SetData("DataDirectory", "C:\myDB");  // SQL Connection String with |DataDirectory| substitution string SqlConnection c = new SqlConnection (    @"Data Source=.\SQLDB; AttachDbFilename=|DataDirectory|\Database.mdf;Initial Catalog=Master"); 

Answer 2

In the MSDN social forums this answer can be found

|DataDirectory| (enclosed in pipe symbols) is a substitution string that indicates the path to the database. It eliminates the need to hard-code the full path which leads to several problems as the full path to the database could be serialized in different places. DataDirectory also makes it easy to share a project and also to deploy an application.

For example, instead of having the following connection string:

"Data Source= c:\program files\MyApp\Mydb.sdf" 

Using DataDirectory, you can have the following connection string:

“Data Source = |DataDirectory|\Mydb.sdf” 

To set the DataDirectory property, call the AppDomain.SetData method. If you do not set the DataDirectory property, the following default rules will be applied to access the database folder:

• For applications that are put in a folder on the user's computer, the database folder uses the application folder.
• For applications that are running under ClickOnce, the database folder uses the specific data folder that is created.