Localized Property with NHibernate

This is a annoying issue we saw again an again.

The story

Three weeks ago Gustavo Fuentes asked me a solution to implement a multi-language property. After heard his needs my first answer was : “go to IUserType”. He was not completely convinced by my answer and so I gave him some links. Few days after Michal Gabrukiewicz asked the solution, for the same problem, in nhusers-list (how much little is the world of IT, no?). Michal have shared his solution in his blog. Immediately I sent the link to Gustavo but, another time, he does not like it (que hincha pelotas). Five days ago, inspired by an IUserType in uNhAddIns, Gustavo shared his own solution in uNhAddIns issue tracker. As usual in Open Sources, when you share your code, somebodyelse can:

1. see it
2. use it
3. find bugs
4. fix bugs
5. improve the solution

Waiting results of the election day in Argentina, I have applied the five points to the Gustavo’s solution.

The LocalizablePropertyType

The LocalizablePropertyType is a IUserType and IParameterizedType implementation that map a IDictionary<CultureInfo, string> to a VARCHAR (or what defined in your dialect for a string).

Your entity may look like:

public class EntityWithLocalizableProperty
{
public virtual IDictionary<CultureInfo, string> LocalizedDescriptions
{
  get; set;
}
}

And your mapping like

<typedef name="localizable"
   class="uNhAddIns.UserTypes.LocalizablePropertyType, uNhAddIns"/>

<class name="EntityWithLocalizableProperty">
<id type="int">
  <generator class="native"/>
</id>
<property name="LocalizableDescriptions" type="localizable"/>
</class>

The LocalizablePropertyType has two parameters:

<typedef name="localizable"
   class="uNhAddIns.UserTypes.LocalizablePropertyType, uNhAddIns">
<param name="keyValueEncloser">~</param>
<param name="length">560</param>
</typedef>

The keyValueEncloser is a char used to enclose the culture-Info name and the value of the localizable string.

The length is the total length of the field in the DB.

Single string property

If you need a single property to represent the value, for the current culture, its implementation may look like:

public virtual string Description
{
get
{
  return
      LocalizedDescriptions.Count > 0 ?
          LocalizedDescriptions.FirstOrDefault
              (
                  e =>
                  e.Key.Equals(Thread.CurrentThread.CurrentCulture)
              )
              .Value
      : null;
}
set
{
  if (value == null)
  {
      LocalizedDescriptions.Remove(Thread.CurrentThread.CurrentCulture);
  }
  else
  {
      LocalizedDescriptions[Thread.CurrentThread.CurrentCulture] = value;
  }
}
}

How is represented a value

Give a dictionary like this:

new Dictionary<CultureInfo, string>
{
 {new CultureInfo("es-AR"), "Hola"},
 {new CultureInfo("en-US"), "Hello"}
};

its persistent representation, using the char ‘~’ as keyValueEncloser, will be:

~es-AR~~Hola~~en-US~~Hello~

Querying

In term of usability inside the entity class I like very much this solution, perhaps the problem is during querying.

I have used the keyValueEncloser not only to remove some bugs but essentially to simplify commons queries over the localized value. After that I have implemented some extension and some helpers to use in queries.

Given an entity initialized like this

new EntityWithLocalizableProperty
{
 LocalizableDescriptions =
     new Dictionary<CultureInfo, string>
         {
             {new CultureInfo("es-AR"), "Hola"},
             {new CultureInfo("en-US"), "Hello"}
         }
};

by HQL:

s.CreateQuery("from EntityWithLocalizableProperty e where e.LocalizableDescriptions like :pTemplate")
.SetString("pTemplate", Localizable.ConvertToLikeClause("en-US", "H_l%"));

by Criteria:

s.CreateCriteria<EntityWithLocalizableProperty>()
.Add(Localizable.Like("LocalizableDescriptions", "en-US", "H_ll_"));

or using the current culture

s.CreateQuery("from EntityWithLocalizableProperty e where e.LocalizableDescriptions like :pTemplate")
.SetString("pTemplate", "H_l%".ToLocalizableLikeClause())

and by Criteria:

s.CreateCriteria<EntityWithLocalizableProperty>()
.Add(Localizable.Like("LocalizableDescriptions", "H_ll_"))

In practice the Localizable class is the responsible to convert a common values used in the Like clause to the right value following the persistent representation defined above (you can see some others overloads).

The Code

The implementation of LocalizablePropertyType is available in uNhAddIns.