NullReferenceException trying to read connection string

Question

I have two projects. One is web & the other is windows forms. Web project connects to database but the windows project throws an exception NullReferenceException reading the connection string.

I am using the same classes to connect both projects. Connection is established using LINQTOSQL.

Here is my Connection string:

<connectionStrings>
    <add name="GPSystemConnectionString"
         connectionString="Data Source=.;Initial Catalog=GPSystem;User ID=***;Password=***"
         providerName="System.Data.SqlClient" />
</connectionStrings>

This is how i am reading it.

string CS = ConfigurationManager.ConnectionStrings["GPSystemConnectionString"].ConnectionString;

(Exception occurs on this line)..... (Object reference not set to an instance of an object.)

Note: i am using same class to connect both projects.... one connects but the other fails.

Please any one help me with this!

Thank you in advance.

Answer 1

You need to have entry in app.config for connection string in your window application.

If you don't have App.Config file then add it.

and put entry like below

<?xml version="1.0"?>
<configuration>
  <connectionStrings>
    <add name="GPSystemConnectionString"  connectionString="..." />
  </connectionStrings>
</configuration> 

In you .cs file

using System;
using System.Configuration;
using System.Data;
using System.Data.SqlClient;
using System.Windows.Forms;

var connectionString=ConfigurationManager.ConnectionStrings["GPSystemConnectionString"].ConnectionString;

Answer 2

I always struggle with this issue of null reference with the ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString when I have the data access layer in a different project/library than the executable. I often use the following to help debug the location of the configuration file at runtime:

var configfile = ConfigurationManager.OpenExeConfiguration(ConfigurationUserLevel.None);
var path = configfile.FilePath;