Getting a ConnectionString from app.config

问题

I have a Web project which calls a library project (DataAccess) to retrieve some data from the database. I added an App.config file (Add -> New Item -> Application Configuration File) to the DataAccess project and added a connectionString section like this:

<configuration>
  <connectionStrings>
    <add name="local"
        connectionString="Data Source=.\sql2008;Initial Catalog=myDB;Integrated Security=True"
        providerName="System.Data.SqlClient" />
  </connectionStrings>
</configuration>

In the DataAccess project, I have the BuildConnection method:

internal static SqlConnection BuildConnection()
{
    string connectionString = ConfigurationManager.ConnectionStrings["local"].ToString();
    return new SqlConnection(connectionString);
}

When I call the method from the Web project, it throws a null exception complaining that the "local" connection string doesn't exist. After debugging it for a while I added the same connection string to the Web.config of the Web project, and now it works fine. The problem though is that I want to isolate the DataAccess project from the Web project, in other words, I want the DataAccess project to use its own app.config file no matter who calls it. Is this even possible? Any help would be appreciated.

回答1:

at runtime, there is just one config file. so the config file of the active project is only considered. also, you cannot have a class library project as an active/startup project i.e.

say you have 4 Projects in your solution, and each of them has a config file, then when you run the application, only the active project's(the one which is your startup project) config file is recognized.

Now what can you do?

if you just want to isolate the sections of the config file, then you can have config file in each of your Projects, which in turn, are referenced in the main projects config i.e.

Web.config:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
   <appSettings file="YourSettings.config">
      <add key="KeyToOverride" value="Original" />
      <add key="KeyToNotOverride" value="Standard" />
   </appSettings>
   <system.web>
        <!-- standard web settings go here -->
   </system.web>

YourSettings.config:

<appSettings>
   <add key="KeyToOverride" value="Overridden" />
  <add key="KeyToBeAdded" value="EntirelyNew" />
</appSettings>

回答2:

An app.config is used when you use in an Application. For a library project using a app config file not helps. Even you put it reference library the code will be in web server. So this type isolation has no sense for any security issue.

But approach of putting things to the right place you are right, the problem is when you reference a dll it doesn't include the dll project's config.

If you want more :) Just read app.config in your lib project and using a code generator create a connection string object such as public static string ConnectionString = $GeneratedCode$;

回答3:

Yes, it's possible.

Your app.config:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
  <appSettings>
    <add key="foo" value="bar"/>
  </appSettings>
</configuration>

Your DataAccess layer:

namespace MyApp.DataAccess
{
    public class DB
    {
        public string cfg;
        public DB()
        {
            var asmName = System.Reflection.Assembly.GetAssembly(this.GetType()).GetName().Name;
            var asmPath = System.Web.HttpContext.Current.Server.MapPath(@"bin\" + asmName + ".dll");
            var cm = ConfigurationManager.OpenExeConfiguration(asmPath);
            this.cfg = cm.AppSettings.Settings["foo"].Value;
        }
    }
}

Here's how to use it:

namespace MyApp.WebApp
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            var db = new MyApp.DataAccess.DB();
            Response.Write(db.cfg);
        }
    }
}

When you compile data access project, it'll generate a MyApp.DataAccess.dll.config out of your app.config content. Add MyApp.DataAccess.dll.config and MyApp.DataAccess.dll to your web app project and make sure to mark Copy To Output Directory to Copy if newer for MyApp.DataAccess.dll.config.

来源：https://stackoverflow.com/questions/15699202/getting-a-connectionstring-from-app-config

标签

connection-string

app-config