Question

Say I have defined a custom AdapterElement : ConfigurationElement with properties Type, Name and Version. Since Name and Version uniquelly identifies the Type property, I would like to enforce the configuration file to have one of the following structures:

<adapter type="TypeOfAdapter"/>
<adapter name="NameOfAdapter" version="VersionOfAdapter"/>

I could easily mark those three properties with IsRequired = false and let users specify the combination the want. However, the following combinations are not valid and I would like to forbid them:

<adapter type="TypeOfAdapter" version="VersionOfAdapter"/>
<adapter type="TypeOfAdapter" name="NameOfAdapter"/>

Is there any easy way of achieving this?

Answer 1

I had to do a bit of reading around to find answers on this one.

How about adding a PostDeserialise check for validity to your AdapterElement class?

protected override void PostDeserialize()
{
   bool isValid = Type != null && Name == null && Version == null
               || Type == null && Name != null && Version != null;
   if (!isValid)
   {
      throw new ArgumentException("Must specify either Type or Name and Version");
   }
   base.PostDeserialize();
}

According to a blog I found there is no more obvious way of verifying validity of Multiple Attributes on a single configuration section – but it appears to be true for configuation elements too.