Get connection string from App.config

Question

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.

Solution 1

You can just do the following:

var connection = 
    System.Configuration.ConfigurationManager.
    ConnectionStrings["Test"].ConnectionString;

Your assembly also needs a reference to System.Configuration.dll

Solution 2

Since this is very common question I have prepared some screen shots from Visual Studio to make it easy to follow in 4 simple steps.

Solution 3

string str = Properties.Settings.Default.myConnectionString; 

Solution 4

Also check that you've included the System.Configuration dll under your references. Without it, you won't have access to the ConfigurationManager class in the System.Configuration namespace.

Solution 5

First Add a reference of System.Configuration to your page.

using System.Configuration;

Then According to your app.config get the connection string as follow.

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

That's it now you have your connection string in your hand and you can use it.

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Comments

[David Colwell]

Love this answer. By default in my version of VS (VS2012 Ultimate) this library is not included, but using System.Configuration still works

[FrenkyB]

What if app.config is added as a link to a project ?

[Amit Sinha]

I did the same as u said but same null reference error I am getting.

[Jacqlyn]

I know that this is a C# question, but since this is the top of the google search results, to do this in VB, it's System.Configuration.ConfigurationManager.ConnectionStrings(‌​"Test").ConnectionSt‌​ring for those of us who have to maintain VB code

[CodingYourLife]

I really HAD TO add the reference or the using was not underlined but still ConfigurationManager unknown. Thanks!

[BrainSlugs83]

This will only work if your connection string is an app setting, it will not work if to retrieve <connectionStrings> elements from app.config (which is what the OP is asking for!).