Get connection string from app.config

Question

I'm trying to make this simple call:

DataContext dc = new DataContext(ConfigurationManager.ConnectionStrings["MyDB"].ConnectionString)

And here's my app.config file:

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <connectionStrings>
    <add name="MyDB" connectionString="Server=STEVEN-PC;Database=MyDB;Trusted_Connection=yes;" />
  </connectionStrings>
</configuration>

But I'm getting an error: Object reference not set to an instance of an object.

It can't find the connection string. What am I doing wrong?

@Inuyasha - I have a Visual Studio solution with several projects. The app.config and the file I'm making the call from are in the same project. — Steven, May 16 '11 at 01:32
I always like to confirm my assumptions by doing things like separating the call to the app.config from the instantiating the dataContext. Just to make sure that is where I'm failing. You're probably right, but every now and then it reveals something unexpected. — Richard Brightwell, May 16 '11 at 01:36
You mention there are several projects. Is the one with the app.config your startup project? If not, you'll have to add your connection string to an app.config in the startup project. — Pete M, May 16 '11 at 01:44

score 15 · Accepted Answer · answered May 16 '11 at 01:44

A common mistake is trying to read a connection string from an app.config from a referenced project instead of from the executable project (the web site or .exe project). You may need to copy the config settings containing the connection string to your main config file.

score 1 · Answer 2 · answered May 16 '11 at 01:38

1

Double check the existence and contents of your configuration file in the build directory. That code should work fine if the config file is in place.

You could also pull put the connection string into a local variable so you can be sure the null reference exception is happening where you think it is.

answered May 16 '11 at 01:38

Josh

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That second paragraph is exactly what I was thinking. I'd try that. – Richard Brightwell May 16 '11 at 01:44
I set the connection string to a local variable, it is where I'm getting the null reference exception. – Steven May 16 '11 at 01:48

score 0 · Answer 3 · answered May 16 '11 at 01:45

0

You might need to specify the providerName:

<add name="MyDB" connectionString="Server=STEVEN-PC;Database=MyDB;Trusted_Connection=yes;" providerName="System.Data.SqlClient" />

answered May 16 '11 at 01:45

Brandon Montgomery

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That's not necessary and even if it were specified, his code isn't accessing that property. – Josh May 16 '11 at 01:48

Get connection string from app.config

3 Answers3

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