Object Reference Not Set to Instance of an Object

Question

Is my machine playing me today?

When I run the TestConnectionString() method of this object I get the error at the connection string setting.

public class CustomerDAL
{
   string connectionString = ConfigurationManager.ConnectionStrings["myConnection"].Name;

    public CustomerDAL()
    {

    }

    public string TestConnection()
    {
        System.Data.SqlClient.SqlConnection conn =  new System.Data.SqlClient.SqlConnection(connectionString);
        conn.Open();

        if (conn.State == System.Data.ConnectionState.Open)
        {
            return "Open";
        }
        else
        {
            return "Close";
        }
     }
}

Jon Skeet · Accepted Answer · 2009-03-30 23:07:40Z

7

If ConnectionStrings["myConnection"] returns null, then dereferencing it to get the Name property will fail in the constructor. Is that definitely not where the bug is?

Why not put a breakpoint on that line and take a look in ConfigurationManager.ConnectionStrings to check what it thinks it's got - and check very carefully for typos.

After that, put a breakpoint on the first line of the method, and check what the value of connectionString is. Passing in null to the SqlConnection constructor doesn't actually throw an exception, but you'd get an InvalidOperationException when you try to open it.

answered Mar 30, 2009 at 23:07

Jon Skeet

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1 Comment

Saif Khan Over a year ago

Jon ~ I should've known better. I've got my StackOverFlowed. It was under "appSettings" section.

Bo Persson · Accepted Answer · 2011-08-06 13:53:43Z

1

I have three suggestions

you need to add a .dll reference for configuration manager
recheck if your connection string is right
check if you have more than one configuration file ex. web.config and app.config; so the ConfigurationManager is referencing the wrong file in the solution.

edited Aug 6, 2011 at 13:53

Bo Persson

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answered Aug 5, 2011 at 21:39

Mahfuz Hussien

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