Configure Your Apps

The Configuration Management Application Block provides simple, flexible, and extensible read/write access to configuration data.

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LANGUAGES: C# | VB .NET | XML

ASP.NET VERSIONS: 1.0 | 1.1

 

Configure Your Apps

The Configuration Management Application Block provides simple, flexible, and extensible read/write access to configuration data.

 

By Brian Noyes

 

The .NET Framework provides a standard and easy to use approach to reading in configuration data for your applications through XML .config files. If your app is an ASP.NET application, the .config file is the web.config file that resides in the application root directory or sub-folder. If your app is a Windows application, the .config file is a file with the same name as the app with a .config extension (i.e. myapp.exe.config) that resides in the same folder as the executable itself.

 

There are classes available in the .NET Framework that make it easy to read in key-value pairs from an appSettings section, or to create your own custom configuration sections and write classes to read in those sections as a chunk of structured data. Using these capabilities, you can avoid hard coding values that may change over time. The prototypical example of a piece of information that you need at run time, but that may change, is a connection string to the database.

 

However, there are many places where the built-in capabilities in .NET fall short. For one thing, the data in .config files is treated as read-only data that is stored in a plain text XML file in the application directory. What if you have runtime modifiable values you want to save back out? What if you want to protect the data you are reading and writing, by storing in a different location in the file system, in the registry, or in a database? What if you want to protect the data further by encrypting it? And probably most importantly, what if you may want to change some of these options over time without having to rebuild and re-deploy your application?

 

Over time, people have come up with a variety of solutions to these problems, resulting in more infrastructure code that they have to write and maintain. Microsoft has now provided a best-practices solution that addresses all these issues in the form of the Configuration Management Application Block (CMAB). This is one of the Microsoft Application Blocks for .NET available free for download through the patterns and practices group on MSDN (http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnbda/html/cmab.asp).

 

To use the CMAB, you first must download the code from MSDN. You can choose between C# and VB .NET implementations. What you get is a class library project that you can compile and use directly in your own apps, sample code that demonstrates the use of the block, and documentation that describes its design and use.

 

You'll Need to Talk to My Manager

The CMAB consists of a number of classes designed to work together to form a mini-framework for the reading and writing of configuration data from/to a variety of storage providers. Using the CMAB in your application code is simplicity itself - you make calls to the Read and Write methods of the ConfigurationManager class, passing an object that contains the data that you want to read or write. Where the data is actually stored is transparent to the calling code.

 

The storage location is driven by entries that you place in the application configuration (.config) file. The CMAB ships with providers for XML files (including the .config file itself or other XML files), SQL Server, and the Registry. You also use the .config file to set up mappings between types of information you will store, and the configuration section handlers that do the loading and writing of that data. Finally, you put settings in the .config file that determine whether the data is cached and/or encrypted, and if encrypted, what data protection provider to use. Although configuring the configuration management block with a configuration file may sound like some horrific circular logic, it should make sense after you see the CMAB in action. Figure 1 shows the way all the pieces of an application using the CMAB play together.

 


Figure 1. To use the CMAB, you call Read or Write on the ConfigurationManager class. The CMAB uses configuration section handlers that you usually provide to figure out how to serialize the data. The CMAB figures out what section handlers to use based on your config file, as well as other CMAB options such as caching and encryption. The CMAB then uses storage providers and data protection providers to persist your data to and from the stores.

 

Get Your Hands Dirty

Let's start with a simple example of using the CMAB with the minimum code required. The CMAB includes one configuration section handler that lets you easily read and write key-value pairs using a Hashtable object. Using that handler, you can start using the Configuration Manager class to read and write data as shown in Figure 2. Note that there are no specifics about where or how the data gets stored in the application code. Again, all those details are set through the application .config file.

 

private void btnRead_Click(object sender, System.EventArgs e)

{

   // Read the value out of the hashtable by its key name

   string connStr = ConfigurationManager.Items["connStr"] as string;

   // Add it to the text box

   txtConnStr.Text = connStr;

}

 

private void btnWrite_Click(object sender, System.EventArgs e)

{

   // Make sure the configuration manager is initialized

   Hashtable values = new Hashtable();

   // Write an empty hashtable into the manager to initialize

   // the storage - just needs to be done once in the app

   ConfigurationManager.Write(values);

   // Now write items into that storage

   ConfigurationManager.Items["connStr"] = txtConnStr.Text;

}

Figure 2. Reading and writing configuration data with a Hashtable is a simple matter of using the Items collection on the ConfigurationManager object. You will need to add a Microsoft.ApplicationBlocks.ConfigurationManagement statement to the beginning of the file to avoid fully qualifying the ConfigurationManager class name.

 

If you configure your app to use the XmlHashtableSectionHandler to read and write the data, you end up with an element like the one shown in Figure 3 in storage.

 

  

    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">

    

      

        connStr

        

          server=localhost;database=Northwind;trusted_connection=true

        

      

    

  

Figure 3. The XmlHashtableSectionHandler writes out the Hashtable in a serialized form to whatever storage location is configured for the app.

 

Where this element gets written will depend on the storage provider you have configured for the application. The storage providers get set through the configuration section in your .config file. In the case of the sample app that accompanies this article, the XmlFileStorage provider is used without specifying a separate file location, so the data is simply stored as a separate configuration section within the .config file itself. If a different storage provider were used (i.e. SQL Server or the Registry), this XML would be written out as a string to that storage location, and could potentially be encrypted if a data protection provider were specified.

 

In Figure 4, you can see a trimmed down version of the entire configuration file for the sample application (with type names and assemblies occluded for readability). The configMgmt named section contains the settings that drive the ConfigurationManager and supporting classes. The first thing you will see is that the defaultSection is set to MyAppSettings, which is the section we saw before that contains the actual Hashtable data. The configMgmt section is tied to the ConfigurationManagerSectionHandler in the configSections element. This is the section that the ConfigurationManager will look for to determine its behavior at run time.

 

  

    

    

  

  

    

      

      

        type="..." refreshOnChange="true"

        signed="false" encrypted="false" />

    

  

  

    ...

  

Figure 4. The sample application .config file. The configMgmt named section is used by the ConfigurationManager to drive the run-time behavior of the block.

 

The ConfigurationManagerSectionHandler will look for three sub-elements under the named section element. The first and only required one is the element. This is the element that identifies the storage provider. In the case of the sample application, the XmlFileStorage provider is identified. The lets you configure whether the data read in is cached, and when that cached data should be expired. See the docs for a full explanation of the options there. The final element that is not shown in the sample is a element under which you can configure encryption information for a data protection provider that will be used when reading and writing the data.

 

That is all there is to the minimal usage of the CMAB. Just do your reading and writing of key-value pairs through the ConfigurationManager class, set up a configuration section for the CMAB itself telling it to use the XmlFileStorage provider, and one for the section that will hold your data using the XmlHashtableSectionHandler.

 

Note: If you are writing data to the config file like in the download SimpleCMABUse Windows application, and you are running a debug session in Visual Studio, you may think the CMAB is not working correctly because any data you write out is not in your config file on the next run. This is because if you have an app.config file as part of your project, VS .NET copies that file down into your debug directory on every run and overwrites the .exe.config file (where is the name of your app). You'll need to inspect the contents of that file in your debug directory between runs to see that the changes are being written, or run outside the debugger so that the file does not get overwritten.

 

Store Custom Object Data

If you really want to take advantage of the capabilities of the CMAB, you won't just read and write key-value pairs to store all your configuration data. Instead, you will want to store your objects as objects without having to worry about breaking them out into atomic values that you can stuff in key-value pairs. To do that, you'll need to do a little extra coding and implement your own configuration section handler.

 

The CMAB always stores data as XML. To translate your custom objects into an XML representation, you implement a custom configuration section handler. If you only need to read data from your configuration stores, then you write a class that implements the IConfigurationSectionHandler interface, which is defined in the System.Configuration namespace. This interface has one method, Create which is called by the ConfigurationManager to read your persisted data in XML format and return it to you as an object. In your implementation of this method, you take the XmlNode that is passed to you that contains the data, and do whatever needs to be done to re-hydrate it into an instance of the object that it represents. The simplest way to do this is to make sure that the XML that gets stored in the configuration store is in an XML serialized format so that you can just deserialize it into an object instance, as shown in Figure 5.

 

public object Create(object parent, object configContext, XmlNode section)

{

   // Get a reader to deserialize into memory,

   //placing the xml fragment into it

   StringReader reader = new StringReader(section.OuterXml);

   // Deserialize from the string reader into an

   //instance of our custom data class

   return m_serializer.Deserialize(reader);

}

Figure 5. The Create method of the IConfigurationSectionHandler is where you take the stored XML representation of your data and convert it back into an object instance. XML serialization is the easiest way to do this.

 

If you also want to write data out to your configuration store, you will also need to implement the IConfigurationSectionHandlerWriter interface, which is defined in the namespace for the CMAB interfaces. This interface just requires a single Serialize method implementation that takes an object as an argument and returns an XmlNode that can then be persisted to the configuration store by the ConfigurationManager.

 

The download code for this article contains another sample application called CMABSample, which is a simple ASP.NET Web application that stores links to Favorites in a configuration store (see end of article for details). It uses the CMAB to read and write the collection of links to a configuration store. It is set up to use the SQL Server configuration store provided with the CMAB, and looks up the configuration string in the registry. It also uses a custom section handler as described above to store the collection of Favorites. See the readme in the download code for detailed instructions on getting the sample up and running on your machine.

 

The CMAB provides a great, easy to use, flexible, and extensible solution to reading and writing configuration data for your apps. In your application code, you just read and write to the ConfigurationManager. Through your config file, you can drive where the data gets stored, whether it is cached, whether it gets encrypted before storage, and if so, how. Unless you have trivial read-only requirements for a few key-value pairs of data for your apps, I recommend you look into using the CMAB as a standard part of your applications for storing and reading configuration data.

 

The code for this article is available for download.

 

Brian Noyes is a consultant, trainer, speaker, and writer with IDesign, Inc. (http://www.idesign.net), a .NET focused architecture and design consulting firm. Brian specializes in designing and building data-driven distributed applications. He has more than 12 years experience in programming, engineering, and project management, and is a contributing editor for C#PRO, asp.netPRO, and other publications. Contact him at mailto:[email protected].

 

 

 

 

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