Best way to implement Entity with translatable properties in NHibernate - nhibernate

Question

Consider the following class (simplified in order to focus in the core problem):
public class Question
{
public virtual string QuestionId { get; set; }
public virtual string Text { get; set; }
public virtual string Hint { get; set; }
}
and tables:
Question
- QuestionId ((primary key, identity column and key)
- Code
QuestionTranslation
- QuestionTranslationId (primary key, identity column; not really relevant to the association)
- QuestionId (composite key element 1)
- CultureName (composite key element 2) (sample value: en-US, en-CA, es-ES)
- Text
- Hint
How I can map the Question class so the Text and Hint properties are populated using the current thread's culture. If the thread's culture is changed I would like the Text and Hint properties to automatically return the appropriate value without the need for the Question entity to be reloaded.
Note that I'm only outlining the relevant class and properties from the business side. I'm totally open to any new class or property needed to achieve the desired functionality.

Answer 1

An alternative to Firo's answer (yes, I copied it and adapted it and feel bad about this).
It uses a dictionary and maps the translations as composite element (so it doesn't need the id at all)
public class Question
{
public virtual string QuestionId { get; set; }
public virtual string Text
{
get
{
var translation = Translations[CultureInfo.CurrentCulture.Name];
if (translation != null) return translation.Text
return null;
}
set
{
GetTranslation(CultureInfo.CurrentCulture.Name).Text = value;
}
}
public virtual string Hint
{
get
{
var translation = Translations[CultureInfo.CurrentCulture.Name];
if (translation != null) return translation.Hint
return null;
}
set
{
GetTranslation(CultureInfo.CurrentCulture.Name).Hint = value;
}
}
private QuestionTranslation GetTranslation(CultureInfo.CurrentCulture.Name)
{
QuestionTranslation translation;
if (!Translations.TryGetValue(CultureInfo.CurrentCulture.Name, out translation))
{
translation = new QuestionTranslation()
Translations[CultureInfo.CurrentCulture.Name] = translation;
}
return translation;
}
protected virtual IDictionary<string, QuestionTranslation> Translations { get; private set; }
}
class QuestionTranslation
{
// no id, culture name
public virtual string Text { get; set; }
public virtual string Hint { get; set; }
}
mapping:
<class name="Question">
<id name="QuestionId" column="QuestionId"/>
<map name="Translations" table="QuestionTranslation" lazy="true">
<key column="QuestionId"/>
<index column="CultureName"/>
<composite-element class="QuestionTranslation">
<property name="Text"/>
<property name="Hint"/>
</composite-element>
</bag>
</class>

Answer 2

Edited to reflect changed answer:
public class Question
{
public virtual string QuestionId { get; set; }
public virtual string Text
{
get
{
var currentculture = CultureInfo.CurrentCulture.Name;
return Translations
.Where(trans => trans.CultureName == currentculture)
.Select(trans => trans.Text)
.FirstOrDefault();
}
set
{
var currentculture = CultureInfo.CurrentCulture.Name;
var translation = Translations
.Where(trans => trans.CultureName == currentculture)
.FirstOrDefault();
if (translation == null)
{
translation = new QuestionTranslation();
Translations.Add(translation);
}
translation.Text = value;
}
}
public virtual string Hint
{
get
{
var currentculture = CultureInfo.CurrentCulture.Name;
return Translations
.Where(trans => trans.CultureName == currentculture)
.Select(trans => trans.Hint)
.FirstOrDefault();
}
set
{
var currentculture = CultureInfo.CurrentCulture.Name;
var translation = Translations
.Where(trans => trans.CultureName == currentculture)
.FirstOrDefault();
if (translation == null)
{
translation = new QuestionTranslation();
Translations.Add(translation);
}
translation.Hint = value;
}
}
protected virtual ICollection<QuestionTranslation> Translations { get; set; }
}
class QuestionTranslation
{
public virtual int Id { get; protected set; }
public virtual string CultureName { get; set; }
public virtual string Text { get; set; }
public virtual string Hint { get; set; }
}
<class name="Question" xmlns="urn:nhibernate-mapping-2.2">
<id name="QuestionId" column="QuestionId"/>
<bag name="Translations" table="QuestionTranslation" lazy="true">
<key>
<column name="QuestionId"/>
</key>
<one-to-many class="QuestionTranslation"/>
</bag>
</class>
<class name="QuestionTranslation" table="QuestionTranslation" xmlns="urn:nhibernate-mapping-2.2">
<id name="QuestionTranslationId"/>
<many-to-one name="ParentQuestion" column="QuestionId"/>
</class>
if you have a lot of translations then change ICollection<QuestionTranslation> Translations { get; set; } to IDictionary<string, QuestionTranslation> Translations { get; set; } and map as <map> but normally the above should do it