Retrieving a ConnectionString through System.Configuration Throws Exception

问题

In my C# application, i am trying to connect to a DataConnection. The application is just a simple Login form but as soon as the user clicks the login button, it throws an exception error referencing the Connection String. Can anyone help?

public void userLoginSuccessfull()
{
    try
    {
        //////////////////////////////////
        // This line is throwing the error
        //////////////////////////////////
        string connString = System.Configuration.ConfigurationManager
            .ConnectionStrings["connectionString"].ConnectionString;

        if (txtUsername.Text != "" & txtPassword.Text != "")
        {
            string queryText = @"SELECT Count(*) FROM Users 
                     WHERE Username = @Username AND Password = @Password";

            using (SqlConnection cn = new SqlConnection(connString))
            using (SqlCommand cmd = new SqlCommand(queryText, cn))
            {
                cn.Open();
                cmd.Parameters.AddWithValue("@Username", txtUsername.Text);
                cmd.Parameters.AddWithValue("@Password", txtPassword.Text);
                int result = (int)cmd.ExecuteScalar();
                if (result > 0)
                {
                    loadUserForm();
                }
            }
        }
    }
    catch (Exception ee)
    {
            Console.WriteLine(ee.StackTrace);
    }
}

This is the error

'EnviroWaste Job Logger.vshost.exe' (CLR v4.0.30319: EnviroWaste Job Logger.vshost.exe): Loaded 'C:\Users\listm\Documents\Visual Studio 2013\Projects\EnviroWaste Job Logger\EnviroWaste Job Logger\bin\Debug\EnviroWaste Job Logger.exe'. Symbols loaded.

A first chance exception of type 'System.Configuration.ConfigurationErrorsException' occurred in System.Configuration.dll

Configuration system failed to initialize

A first chance exception of type 'System.TypeInitializationException' occurred in System.Data.dll

The connection string looks like this:

connectionString="Data Source=(LocalDB)\v11.0;AttachDbFilename=|DataDirectory|\UsersDatabase.mdf;Integr‌ated Security=True"

回答1:

The error you got relates to a configuration file that has incorrect content. Most likely, your app.config (if desktop) or web.config (if web app) file the following error:

It does not have as its first element the <configSections> element.

Check that file and make sure it looks something like this

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <configSections>
        <!-- Section groups, and stuff like userSettings, etc  -->
    </configSections>

    <connectionStrings>
        <add name="connectionString" connectionString="Data Source=(LocalDB)\v11.0;AttachDbFilename=|DataDirectory|\UsersDatabase.mdf;Integr‌ated Security=True"/>
    </connectionStrings>

    <!-- Possibly other stuff  -->

</configuration>

回答2:

Also ran into the same problem. The explanation Alex provided gives a clue into the issue however it is not enough.

The app.config apparently expects the elements to appear in a certain order.

Therefore, in app.config, right after <configuration>, the first section MUST be:

<configSections>
    <!-- Section groups, and stuff like userSettings, etc  -->
</configSections>

Followed by the

<connectionStrings>
    <add name="connectionString" connectionString="...whatever is here..."/>
</connectionStrings>

And then comes the rest.

In my case, I had:

<system.data>
  <DbProviderFactories>
    <remove invariant="System.Data.SQLite.EF6" />
    <add name="SQLite Data Provider (Entity Framework 6)" invariant="System.Data.SQLite.EF6" description=".NET Framework Data Provider for SQLite (Entity Framework 6)" type="System.Data.SQLite.EF6.SQLiteProviderFactory, System.Data.SQLite.EF6" />
  </DbProviderFactories>

As the very first element after <config&gt.

All I needed to was to move the <system.data> section and place it AFTER the <connectionStrings>, in order to respect the order that VS needs.

So in addition to needing to have the <configSections> before <connectionString> these must also be the two first sections right after <config&gt. This is what fixed it for me.

来源：https://stackoverflow.com/questions/29835821/retrieving-a-connectionstring-through-system-configuration-throws-exception

标签

connection-string