Question

Is it possible to Deserialize the following piece of XML into a Dictionary<int,string> object?

XML:

<Config>

<DatabaseConnections>
     <Connection Name="Source Connection" Value="ConnectionStringValue" />
     <Connection Name="Target Connection" Value="ConnectionStringValue" />
<DatabaseConnections>

<Config>

I have a class which will have a property of Dictionary<int,string> {get;set;}

I would like to use the following C# code to do this:

XmlSerializer xs = new XmlSerializer(typeof(Config));

using(StringReader sr = new StringReader(rootnode.OuterXml))
{
      return (Config)xs.Deserialize(sr);
}

Are there any alternatives to doing this?

Answer 1

You cannot use the default XmlSerializer implementation to (de)serialize IDictionary objects to Xml. From the MSDN XmlSerializer documentation:

The XmlSerializer gives special treatment to classes that implement IEnumerable or ICollection. A class that implements IEnumerable must implement a public Add method that takes a single parameter. The Add method s parameter must be of the same type as is returned from the Current property on the value returned from GetEnumerator, or one of that type s bases.

The Dictionary<> class implements both interfaces, but does not have an Add method that takes a single parameter, so it fails.

More to the point, the xml serialization code explicitly disallows classes that implement IDictionary (from Reflector, looking at TypeScope.GetDefaultIndexer):

 if (typeof(IDictionary).IsAssignableFrom(type)) {
        if (memberInfo == null) {
            throw new NotSupportedException(...);
        }
        throw new NotSupportedException(...);
 }

So you can t even make the work by subclassing Dictionary<> and adding the required Add overload.

The article Generic Dictionaries vs. the XmlSerializer describes one workaround:

First, decorate the Dictionary property with an XmlIgnore attribute. This tells the XmlSerializer to ignore that property, eliminating the reflection error.

Create a new public property that takes and returns an array of DictionaryEntry objects. I tend to name these specially (_x_DictionaryName) so that it is clear one should not generally use this property.

Serialize away.

Answer 2

You can use this class: SerializableDictionary.

You will need to change the property type, of course:

public class Config
{
     public SerializableDictionary<String, String> DatabaseConnections
     { get; set; }
}

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