How to Avoid 'Object reference not set to an instance of an object' When Retrieving Connection Strings from App.config?

Accessing Connection Strings from App.config: Avoiding NullReferenceExceptions

Retrieving connection strings from your App.config file requires careful handling to prevent NullReferenceException errors. Consider the following code example:

<code class="language-csharp">var connection = ConnectionFactory.GetConnection(
    ConfigurationManager.ConnectionStrings["Test"]
    .ConnectionString, DataBaseProvider);</code>

This code snippet, when used with a standard App.config file like this:

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

can throw a NullReferenceException if the connection string "Test" is not found. The problem lies in directly accessing .ConnectionString without checking for null.

A robust solution involves verifying the existence of the connection string before accessing its properties:

<code class="language-csharp">var connectionString = ConfigurationManager.ConnectionStrings["Test"];
if (connectionString != null)
{
    var connection = ConnectionFactory.GetConnection(connectionString.ConnectionString, DataBaseProvider);
    // ... use the connection ...
}
else
{
    // Handle the case where the connection string is not found.  
    // Log an error, throw an exception, or use a default connection.
}</code>

Alternatively, a more concise approach using the null-conditional operator (?.) can be employed:

<code class="language-csharp">var connection = ConnectionFactory.GetConnection(
    ConfigurationManager.ConnectionStrings["Test"]?.ConnectionString, DataBaseProvider);</code>

This will gracefully handle the null case by setting connection to null if "Test" is missing. Remember to add appropriate error handling in this scenario.

Finally, remember to include a reference to System.Configuration.dll in your project. This assembly provides the necessary classes for accessing configuration settings. Without this reference, compilation will fail.

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