How to get interpolated message in NHibernate.Validator

Question

I'm trying to integrate NHibernate.Validator with ASP.NET MVC client side validations, and the only problem I found is that I simply can't convert the non-interpolated message to a human-readable one. I thought this would be an easy task, but turned out to be the hardest part of the client-side validation. The main problem is that because it's not server-side, I actually only need the validation attributes that are being used, and I don't actually have an instance or anything else at hand.

Here are some excerpts from what I've been already trying:

// Get the the default Message Interpolator from the Engine
IMessageInterpolator interp = _engine.Interpolator;
if (interp == null)
{
  // It is null?? Oh, try to create a new one
  interp = new NHibernate.Validator.Interpolator.DefaultMessageInterpolator();
}

// We need an instance of the object that needs to be validated, se we have to create one
object instance = Activator.CreateInstance(Metadata.ContainerType);

// we enumerate all attributes of the property. For example we have found a PatternAttribute
var a = attr as PatternAttribute;

// it seems that the default message interpolator doesn't work, unless initialized
if (interp is NHibernate.Validator.Interpolator.DefaultMessageInterpolator)
{
  (interp as NHibernate.Validator.Interpolator.DefaultMessageInterpolator).Initialize(a);
}

// but even after it is initialized the following will throw a NullReferenceException, although all of the parameters are specified, and they are not null (except for the properties of the instance, which are all null, but this can't be changed)
var message = interp.Interpolate(new InterpolationInfo(Metadata.ContainerType, instance, PropertyName, a, interp, a.Message));

I know that the above is a fairly complex code for a seemingly simple question, but I'm still stuck without solution. Is there any way to get the interpolated string out of NHValidator?

Answer 1

Ok, so I know this is an old question, but I stumbled across this when trying to do the same thing, and it helped me get started - so I thought I would provide an answer.

I think the code in the question was on the right track but there are a couple of problems. The interpolator was not completely initialised with the ResourceManager and Culture details, and it doesn't seem to allow for the fact that you can only have one DefaultMessageInterpolator per validation attribute. Also, you don't need an instance of the object you are validating to get an interpolated message.

In the code in the question, where you are initialising the interpolator with the attribute value, you also need to initialise the interpolator with details of the ResourceManager to be used.

This can be done using the overloaded Initialize method on DefaultMessageInterpolator which has the following signature:

    public void Initialize(ResourceManager messageBundle, 
                           ResourceManager defaultMessageBundle, 
                           CultureInfo culture)

The first parameter is a user-defined ResourceManager in case you want to use your own resource file for error messages, you can pass a null if you just want to use the default ResouceManager, the second parameter is the default ResourceManager - you can pass

  new ResourceManager( 
      NHibernate.Validator.Cfg.Environment.BaseNameOfMessageResource,
      Assembly.GetExecutingAssembly());

for this, the last parameter is the culture to use, (NHibernate.Validator comes with resource files with validation messages in several languages) - if you pass a null in to this it will just use CultureInfo.CurrentCulture

Lastly, you can only have one DefaultMessageInterpolator per attribute, so you will need to create a new DefaultMessageInterpolator for each validation attribute. You could make use of the DefaultMessageInterpolatorAggregator to handle this, or just roll your own.

I hope this helps someone.

Answer 2

Thanks for your help all--I'd upvote if I could. I just wanted to add that in addition to the first Initialize call on the DefaultMessageInterpolator that Stank illustrates, I also had to make a second different Initialize call to fully initialize it (I was getting some Null Reference Exceptions using only the first call). My code is as follows:

string interpolatedMessage = "";
DefaultMessageInterpolator interpolator = new DefaultMessageInterpolator();

interpolator.Initialize(null,
    new ResourceManager(
        NHibernate.Validator.Cfg.Environment.BaseNameOfMessageResource,
        Assembly.Load("NHibernate.Validator")),
        CultureInfo.CurrentCulture);

interpolator.Initialize(attribute as Attribute);

if (attribute is IValidator && attribute is IRuleArgs)
{
    IValidator validator = attribute as IValidator;
    IRuleArgs ruleArgs = attribute as IRuleArgs;

    InterpolationInfo interpolationInfo = new InterpolationInfo(
        validatableType, 
        null, 
        propertyName, 
        validator,
        interpolator, 
        ruleArgs.Message);

    interpolatedMessage = interpolator.Interpolate(interpolationInfo);
}