Get connection string from App.config

user_823273 0
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var connection = ConnectionFactory.GetConnection(
    ConfigurationManager.ConnectionStrings["Test"]
    .ConnectionString, DataBaseProvider);

And this is my App.config: 

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <connectionStrings>
        <add name="Test" connectionString="Data Source=.;Initial Catalog=OmidPayamak;Integrated Security=True" providerName="System.Data.SqlClient" />
    </connectionStrings>
</configuration>

But when my project runs this is my error:

Object reference not set to an instance of an object.

connection-string ado.net exception-handling app-config c#
22 Answers

The answers above didn't elaborate where the value in connectionStrings index comes from.

As mentioned above, to get your connection string, you say:

string conStr = ConfigurationManager.ConnectionStrings["XXX"].ToString();

To use the correct value of XXX, go to your main projects web.config file and look for the following piece of code:

<connectionStrings>
    <add name="Authentication" connectionString="Data Source=(LocalDb)\MSSQLLocalDB;Initial Catalog=Authentication;Integrated Security=SSPI;AttachDBFilename=|DataDirectory|\Authentication.mdf" providerName="System.Data.SqlClient" />
</connectionStrings>

Where it says name= , the text within those proceeding quotes is the value of XXX you use in the code above. In my example above, it happens to be Authentication

user_59593720

You can use this method to get connection string

using System; 
using System.Configuration;

private string GetConnectionString()
{
    return ConfigurationManager.ConnectionStrings["MyContext"].ConnectionString;
}
user_86147920

I solved the problem by using the index to read the string and checking one by one. Reading using the name still gives the same error.
I have the problem when I develop a C# window application, I did not have the problem in my asp.net application. There must be something in the setting which is not right.

user_88303750

In order to read the connection string from app.cfg (in windows service application) the below code worked for me

 var config = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
    var connectionStringsSection = (ConnectionStringsSection)config.GetSection("connectionStrings");
    connectionStringsSection.ConnectionStrings["CONNECTIONSTR"].ConnectionString = @"New Connection String";
user_43025520

Encountered this issue while placing ConfigurationManager.ConnectionStrings in UserControl's constructor, and none of the solution here worked for me.

After some research, seems like ConfigurationManager.ConnectionStrings would be null while trying to access it from the DesignTime.

And from this post, I came up with this following code to detect DesignTime as a workaround to the issue:

public class MyUserControl : UserControl 
{
    ....
    public MyUserControl ()
    {
        InitializeComponent();

        bool designMode = (LicenseManager.UsageMode == LicenseUsageMode.Designtime);
        if (!designMode)
        {
            this.connectionString = 
                ConfigurationManager.ConnectionStrings["xxx"].ConnectionString;
        }
    }
}
user_81404730
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