How to read optional attributes in XML with default values

When we are reading data from XML data sources, it is very common that when a value is not given for an attribute or an element, we have to use a default value instead. Having to check for the existence of the node each and every time we are reading a value can be annoying and clutter the code. To address this issue I have made a few useful extension method that you can use copy and use in your code. These are written on top of XAttribute class, but you can write similar methods for other types and APIs pretty much the same way.

public static class XmlExtentions
{
    public static string ValueOrDefault(this XAttribute attr)
    {
        return ValueOrDefault(attr, string.Empty);
    }
    public static string ValueOrDefault(this XAttribute attr, string defaultValue)
    {
        return attr == null ? defaultValue : attr.Value;
    }

    public static T ValueOrDefault<T>(this XAttribute attr, T defaultValue) where T : struct
    {
        if (attr == null) { return defaultValue; }
        var value = attr.Value;
        var convertedValue = typeof(T).IsEnum ? Enum.Parse(typeof(T), value) : Convert.ChangeType(value, typeof(T));
        if (convertedValue == null) { return defaultValue; }
        return (T) convertedValue;
    }

    public static T ValueOrDefault<T>(this XAttribute attr, Func<T> defaultDelegate) where T : struct
    {
        if (attr == null) { return defaultDelegate(); }
        var convertedValue = Convert.ChangeType(attr.Value, typeof(T));
        if (convertedValue == null) { return defaultDelegate(); }
        return (T)convertedValue;
    }
}

Once you get it in place. It is pretty easy to use. Assume that we have the following XML document:

<Configuration>
    <Search Enabled="True" RankingAlghorithm="BS77" LowMark="1000" HighMark="2000">
        <Source Name="Orders" Type="WebService" />
        <Source Name="Products" Type="REST" />
    </Search>
<Configuration>

As is shown below, you can read any type of values exactly the same way.

// reading a bool
var isEnabled = sourceNode.Attribute("Enabled").ValueOrDefault(false);

// reading a string
var scopeName = sourceNode.Attribute("Name").ValueOrDefault("Default");

// reading a string and using empty string (string.Empty) as default value
var scopeName = sourceNode.Attribute("Name").ValueOrDefault();

// reading an enum
var sourceType = sourceNode.Attribute("Type").ValueOrDefault(SearchSources.Html);

// reading an integer
var lowMark = sourceNode.Attribute("LowMark").ValueOrDefault(100);

// Using a delegate to provide the default value
var highMark = sourceNode.Attribute("HighMark").ValueOrDefault(()=> App.GetUserSetting("Search.HighMark"));
How to read optional attributes in XML with default values