.NET 4.8中如何处理含不支持属性的ConfigurationSection？

在.NET 4.8中，当配置文件包含已不再支持的配置节点时，如何正常加载ConfigurationSection？如果更新System.Configuration.ConfigurationSection时移除了不再支持的ConfigurationProperty，能否让客户无需修改.config文件即可正常加载？

示例场景 #

原配置节定义：

public class CustomConfigSection : ConfigurationSection
{
    [ConfigurationProperty("supportedFeatureConfiguration")]
    public SupportedFeatureConfigElement SupportedFeatureConfig => (SupportedFeatureConfigElement)base["supportedFeatureConfiguration"];
    
    [ConfigurationProperty("unsupportedFeatureConfiguration")]
    public UnsupportedFeatureConfigElement UnsupportedFeatureConfig => (UnsupportedFeatureConfigElement)base["unsupportedFeatureConfiguration"];
}

版本更新后移除废弃属性：

public class CustomConfigSection : ConfigurationSection
{
    [ConfigurationProperty("supportedFeatureConfiguration")]
    public SupportedFeatureConfigElement SupportedFeatureConfig => (SupportedFeatureConfigElement)base["supportedFeatureConfiguration"];
}

当前加载配置的代码：

private void DummyCode()
{
    var configuration = ConfigurationManager.OpenExeConfiguration("My Config Path");
    var mySection = configuration.Sections.Cast<ConfigurationSection>().FirstOrDefault(c => c.SectionInformation.Name == "My Section Name");

    if (mySection == null)
    {
        return;
    }

    using (var fs = new FileStream("My File Name", FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
    {
        var xmlDoc = XDocument.Load(fs);
        mySection.SectionInformation.SetRawXml(xmlDoc.ToString());
    }
}

直接移除属性后加载会抛出未识别节点错误，需避免要求所有用户修改.config文件的破坏性变更，寻求更简洁的兼容方案。

1. 重写DeserializeElement方法忽略未知节点 #

这是最简洁且长效的方案，通过重写配置节的DeserializeElement方法，自动跳过无法识别的废弃节点，无需修改客户配置：

public class CustomConfigSection : ConfigurationSection
{
    [ConfigurationProperty("supportedFeatureConfiguration")]
    public SupportedFeatureConfigElement SupportedFeatureConfig => (SupportedFeatureConfigElement)base["supportedFeatureConfiguration"];

    protected override void DeserializeElement(XmlReader reader, bool serializeCollectionKey)
    {
        while (reader.NodeType != XmlNodeType.EndElement)
        {
            if (reader.Name == "supportedFeatureConfiguration")
            {
                // 仅处理仍支持的节点
                base.DeserializeElement(reader, serializeCollectionKey);
            }
            else
            {
                // 跳过所有未知节点（包括废弃的unsupportedFeatureConfiguration）
                reader.Skip();
            }
        }
    }
}

2. 预处理XML移除废弃节点后加载 #

如果不想修改配置节类，可以在加载XML时提前移除废弃节点，再传入配置节：

private void DummyCode()
{
    var configuration = ConfigurationManager.OpenExeConfiguration("My Config Path");
    var mySection = configuration.Sections.Cast<ConfigurationSection>().FirstOrDefault(c => c.SectionInformation.Name == "My Section Name");

    if (mySection == null)
    {
        return;
    }

    using (var fs = new FileStream("My File Name", FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
    {
        var xmlDoc = XDocument.Load(fs);
        // 移除所有废弃的配置节点
        xmlDoc.Descendants("unsupportedFeatureConfiguration").Remove();
        mySection.SectionInformation.SetRawXml(xmlDoc.ToString());
    }
}

3. 保留废弃属性但标记为忽略（过渡方案） #

若需快速兼容且可接受少量冗余代码，可保留废弃属性并标记为Obsolete，同时设置非必填：

public class CustomConfigSection : ConfigurationSection
{
    [ConfigurationProperty("supportedFeatureConfiguration")]
    public SupportedFeatureConfigElement SupportedFeatureConfig => (SupportedFeatureConfigElement)base["supportedFeatureConfiguration"];

    [Obsolete("此配置已废弃，将被忽略")]
    [ConfigurationProperty("unsupportedFeatureConfiguration", IsRequired = false)]
    public UnsupportedFeatureConfigElement UnsupportedFeatureConfig => null; // 不实际读取配置值
}

内容的提问来源于stack exchange，提问作者r_h_w