Can't connect to database server

Question

I'm encountering a problem with my database connection. I started with a new blank solution, then I added a WCF library project, and last but not least a WCF website (service). In the website i added a reference to the library where I have the interface (data contract), the class that implements the interface and the dataclasses. what I'm trying to do is to connect to a database on a server and try to retrieve some data from there. So the connection string looks like:

    <add name="myConnectionString" connectionString="Data Source=MyServer; Initial Catalog=MyDatabase; User Id=me; Password=me123;" providerName="System.Data.SqlClient" />

and this is how I'm trying to connect with the database:

    public List<string> GetEngagements(string id)
    {
        string sql = "SELECT myColumn FROM myTable WHERE Id = '" + id + "'";
        string connString = string.Empty;
        SqlConnection connDB;
        connString = ConfigurationManager.ConnectionStrings["myConnectionString"].ConnectionString;
        connDB = new SqlConnection(connString);
        SqlCommand command = new SqlCommand(sql, connDB);
        connDB.Open();
        SqlDataReader rdr = command.ExecuteReader();
        List<string> numbers = new List<string>();

        while (rdr.Read())
        {
            numbers.Add(rdr[0].ToString());
        }
        rdr.Close();

        return numbers;
    }

I'm getting an exception on connDB.Open(). Then exception message says: Failed to generate a user instance of SQL Server due to a failure in starting the process for the user instance. The connection will be closed.

I've been getting this message for 2 days now, I've googled a lot and deleted the C:\\Documents and Settings\\username\\Local Settings\\Application Data\\Microsoft\\Microsoft SQL Server Data\\SQLEXPRESS directory but it didn't work for me..

Any solution???? help please

Answer 1

The error message:

Failed to generate a user instance of SQL Server due to a failure in starting the process for the user instance.

Suggests that you're using user instancing , and therefore your connection string will point to an .mdf file on disk rather than the name of a database.

So I'll assume that you want to connect to a file instance rather than a server instance.

I'll also assume that you're using SqlExpress rather than the full fat version.

In which case your connection string is wrong. It should look more like this:

"Data Source=.\SQLEXPRESS;
 AttachDbFilename=fileOnDisk.mdf;
 Integrated Security=True;
 User Instance=True;"

User instancing means that this server instance and the DB inside will only be visible to the application opening the connection string.

You don't have to use user instancing - you can set User Instance=False or just leave it out. Then once the application has made the connection you can connect other tools to the server instance and connect to the DB yourself.