Extending ValidationBase to Validate Properties of Type ValidationBase

Extending ValidationBase

Consider the ContactPerson class from my article series on N-Layer design. This class has an Addresses collection that contains zero or more addresses. But what if the ContactPerson only had a single address whose type is Address (which inherits ValidationBase)? In that case, when validating the ContactPerson, you may also want to validate the Address in one fell swoop and show a list of errors to your users like this:

• Enter your first name
• Enter your zip code
• Choose an address type

Fortunately, with just a bit of code, this is easy to implement. In the ValidationBase class, add the following code near the end of the Validate method, just before the return statement:

public virtual bool Validate(bool clearBrokenRules)
{
  ...

  foreach (PropertyInfo property in properties)
  {
    ValidationBase vbase = property.GetValue(this, null) as ValidationBase;
    if (vbase != null && !vbase.Validate())
    {
      foreach (BrokenRule brokenRule in vbase.BrokenRules)
      {
        BrokenRules.Add(new BrokenRule(string.Format("{0}.{1}", 
             property.Name, brokenRule.PropertyName), brokenRule.Message));
      }
    }
  }  

  return (BrokenRules.Count == 0);
}

When you run this code, the Address property is now validated as well. The BrokenRules collection of the ContactPerson now also contains broken rules for the address in the format ParentPropertyName.SubPropertyName, ValidationMessage. So, for example for an Address property whose zip code is not valid, you get an error like:

Address.ZipCode, "Enter your zip code"

You can use these validation rules to build up a list in the UI similar to the way I have done in my article series on N-Layer design.

The cool thing about this solution is that it works recursively. If the Address instance in turn contains another ValidationBase property (like LocationOnEarth) you would end up with a broken validation rule like Address.LocationOnEarth.Long, as shown in the following screen shot of the debugger:

Thanks for the tip, Maarten. I'm sure this comes in handy when dealing with more complex object hierarchies.

Download Files

The modified ValidationBase class (C# only)