Using appSettings values in other Web.config sections

Question

Is there a way to use appSettings defined properties in any of the other sections in web.config file?

It's quite unpleasant to have to write a value (for instance, an email address) in more than one section, and update it everywhere it occurs whenever a change is done.

Kobi · Accepted Answer · 2009-08-12 11:30:56Z

2

You can use String.Format to build your data, and use {0} in the config file, on appropriate places.
Assuming you have basic getters to you're data this should be easy to implement.

For example:

<add key="Mail" value="[email protected]"/>
<add key="LinkFormat" value="[[Mail Us|mailto:{0}]]"/>

And then (stripped down from try/catch, checking data):

public static string GetEmail()
{
    return ConfigurationManager.AppSettings["Mail"];
}

public static string GetEmailLinkformat()
{
    string format = ConfigurationManager.AppSettings["LinkFormat"];
    string mail = GetEmail();
    return String.Format(format, mail);
}

edited Aug 12, 2009 at 11:30

answered Aug 12, 2009 at 11:22

Kobi

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3 Comments

German Latorre Over a year ago

Could you please post an example?

German Latorre Over a year ago

Oh, thanks Kobi, grand example! :-) Anyway I was thinking about any solution that doesn't require any extra coding... But if there's no alternative, that will work, thanks again.

Kobi Over a year ago

On the long run, adding such functions will save time and reduce code duplication. I don't know of a build-in way of doing that, using just the config file.

Dave Anderson · Accepted Answer · 2009-08-12 12:02:33Z

-1

If you use $ delimiters in the AppSetting values these can be replaced with the key values they represent from the AppSettings e.g.

<add key="PrivacyPolicyURL" 
  value="$domain$/Default.aspx?siteid=$siteid$&amp;locid=$locid$&amp;tpid=$tpid$"
  />

using the following function to do the substitutions;

public static string GetAppSetting(string key)
{
    string keyValue = ConfigurationManager.AppSettings[key].ToString();

    foreach (System.Text.RegularExpressions.Match match in System.Text.RegularExpressions.Regex.Matches(keyValue, @"\$[\d\D]*?\$"))
    {
        try
        {
            string replaceWith = ConfigurationManager.AppSettings[match.Value.Replace("$", string.Empty)]  ?? string.Empty;
            keyValue = keyValue.Replace(match.Value, replaceWith);
        }
        catch
        {
            keyValue = keyValue.Replace(match.Value, string.Empty);
        }
    }

    return keyValue;
}

So in the example this inserts the AppSettings for domain, siteid, locid and tpid to produce something like; www.mywebsite.com/Default.aspx?siteid=1001&locid=1001&tpid=1001

answered Aug 12, 2009 at 12:02

Dave Anderson

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1 Comment

German Latorre Over a year ago

That's a nice option too, thanks! However I was more focused on, for instance, use a value declared in the appSettings section in a different section, such as a log4net section. Anyway, I guess that any option will involve some coding, won't it?

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