如果用户缺乏写入权限，如何允许用户修改存储在 app.config 中的连接字符串？

Question

First, some background on our app: When deployed, our application will be installed on a clients machine in the Program Files directory. We use connection strings which are stored in the App.config file that comes with the program. Under most circumstances, these connection strings will never change. However, at some point, it may be possible that the connection string info will go out of date. To that end, we have included a feature in our program that allows the user to enter new database information if the database can't be reached. The information is parsed into a connection string, tested for validity, and written back into the config file if valid. (Yes, this change is intended to affect all users on the computer, since they will be unable to run the application without a valid connection string anyway - if one user knows the DB info, then other users on the same computer will benefit from that knowledge. Writing to App.config instead of a per-user settings file is preferred.)

The problem I'm running into is that the end user will not have admin permissions, and thus will not be able to run our app at a level that allows it to make any changes to its own config file (since it is located in the C:\\Program Files directory). I'm looking at a couple of different options, but I'm having problems implementing each of them:

1. Move config file to a different location. Not possible in this case because we are deploying an executable, and from what I understand, the App.config file must reside in the same directory.

2. Separate the connection string info into an external config file. I know about the configSource property that can be added to the connection string section of App.config. However, I'm having trouble specifying a concrete target. I can't simply put the file alongside the executable (otherwise I'd get the same permissions issues as the regular App.config). However, it appears environment variables (such as %AppData% ) are not supported as valid config sources. I have tried to implement the solution from this question , but the program crashes before I can change the config source to a valid string because the ConfigurationManager apparently attempts to read the config source folder immediately and thus crashes with a FileNotFoundException.

3. Create our own config file implementation. I could always just create a custom class that is dedicated to reading a config file that is located in a specific location, but I would prefer using the built-in ConfigurationManager if possible.

My main question is this: How can I allow the end user (who only has read permissions in the application folder) to modify config settings dynamically when the config file must stay in the application folder?

Answer 1

Since windows xp, the OS prevents programs with out admin privileges from writing to the Program Files folder. The "Program Data" folder was created to allow programs to store persistent information. I always use a custom config file to store program data that an end User needs to config to connect to a database. I also encrypt at least the password of the connection string, but that is a another discussion. I provided a sample class and usage that stores a config file in Program Data Folder.

Config Class

using System;
using System.IO;
using System.Xml.Serialization;

namespace MyNamespace
{
    public class Config
    {

        public string SomeStringProperty { get; set; }
        public int SomeIntProperty { get; set; }

        private static string _filePath = null;

        static Config()
        {
            _filePath = System.Environment.GetFolderPath(System.Environment.SpecialFolder.CommonApplicationData) + @"\My Program Name";
        }

        public static Config LoadConfig()
        {
            if (File.Exists(_filePath))
            {
                try
                {
                    XmlSerializer reader = new XmlSerializer(typeof(Config));
                    StreamReader file = new StreamReader(_filePath);
                    Config config = (reader.Deserialize(file) as Config);
                    return config;
                }
                catch (Exception ex)
                {
                    //Deal With no file file read error here.
                }
            }

            // IF we get here no valid config file was loaded so make a new one.
            return new Config();

        }

        public Exception SaveConfig()
        {
            try
            {
                XmlSerializer writer = new XmlSerializer(typeof(Config));
                StreamWriter file = new StreamWriter(_filePath);
                writer.Serialize(file, this);
                file.Close();
                return null;
            }
            catch (Exception ex)
            {
                return ex;
            }
        }
    }
}

Basic Usage

Config config = Config.LoadConfig();
Debug.WriteLine("SomeIntProperty=" + config.SomeIntProperty.ToString());
Debug.WriteLine("SomeStringProperty=" + config.SomeStringProperty);

config.SomeIntProperty = 10;
config.SomeStringProperty = "Hello";

config.SaveConfig();

Answer 2

var configuration = System.Web.Configuration.WebConfigurationManager.OpenWebConfiguration("~");

var section = (ConnectionStringsSection)configuration.GetSection("connectionStrings");
section.ConnectionStrings["YourNameConnectionString"].ConnectionString = "yourstring";