带有递归ConfigurationElement的自定义配置节

Question

我正在尝试创建一个表示以下xml结构的自定义配置节：

<observerSettings>
   <jobSettings>
      <filter key="location" value="de">
        <filter key="type" value="MyType1">
          <filter key="status" value="failed">
            <actions>
              <notify timespan="12.00:00:00">
                <mailSettings>
                  <mailAddress to="mail1@something.com" />
                  <mailAddress to="mail2@something.com" />
                </mailSettings>
              </notify>
              <remove timespan="14.00:00:00">
                <mailSettings>
                  <mailAddress to="mail1@something.com" />
                  <mailAddress to="mail2@something.com" />
                </mailSettings>
              </remove>
            </actions> 
          </filter>
        </filter>
      </filter>
   </jobSettings>
</observerSettings>

FilterConfigElement的定义如下：

internal class FilterConfigElement : ConfigurationElement, IFilterConfigElement
{
        [ConfigurationProperty("filter", IsRequired = false)]
        public FilterConfigElement ChildFilter => base["filter"] as FilterConfigElement;

        [ConfigurationProperty("actions", IsRequired = false)]
        public ActionsConfigElement Actions => base["actions"] as ActionsConfigElement;

        [ConfigurationProperty("key", IsRequired = true)]
        public string Key => base["key"] as string;

        [ConfigurationProperty("value", IsRequired = false)]
        public string Value => base["value"] as string;
}

当像下面这样访问配置节时，应用程序崩溃，并出现StackOverflow异常：

internal class ObserverSettings : ConfigurationSection, IObserverSettings
{
   public static IObserverSettings Instance { get; private set; } = ConfigurationManager.GetSection("observerSettings") as ObserverSettings;

   [ConfigurationProperty("jobSettings")]
   protected JobSettingsCollection JobSettingsCollection => base["jobSettings"] as JobSettingsCollection;

   public virtual IJobSettingsCollection JobSettings => JobSettingsCollection;
}

因此，我假设ConfigurationManager正在创建具有无限深度的结构，并且在到达最后一个filter元素时不会停止。这能以某种方式受到限制吗？这种结构是否得到了支持？

Answer 1

好的，在深入研究了ConfigurationElement的实现之后，似乎根本不可能像我尝试的那样创建递归结构。

问题的原因是PropertiesFromType的实现，其中将属性分配给s_propertyBags是在调用CreatePropertyBagFromType之后完成的，因此在properties始终为null的情况下创建了无休止的递归。

private static bool PropertiesFromType(Type type, out ConfigurationPropertyCollection result)
{
   ConfigurationPropertyCollection properties = (ConfigurationPropertyCollection)s_propertyBags[type];
   result = null;
   bool firstTimeInit = false;
   if (properties == null) /*code omitted*/
   {
      properties = CreatePropertyBagFromType(type);
      s_propertyBags[type] = properties;
      firstTimeInit = true;
   }
   result = properties;
   return firstTimeInit;
}

来源：https://referencesource.microsoft.com/#System.Configuration/System/Configuration/ConfigurationElement.cs

编辑：

保持某种“递归”结构的唯一解决办法是将所有子FilterConfigElement包装到一个元素名为childFilter的ConfigurationElementCollection中。这导致下面的配置结构不是很好，但可以接受：

<jobSettings>
  <filter key="location" value="de">
    <childFilter>
      <filter key="type" value="MyType1">
        <childFilter>
          <filter key="status" value="failed">
            <actions>
              <!-- ... -->
            </actions>
          </filter>
        </childFilter>
      </filter>
    </childFilter>
  </filter>
</jobSettings>

来源：Recursive Custom Configuration in c#