FluentNHibernate - Mapping a class to multiple tables - nhibernate

Question

Sorry for a lengthy question. But it is worth giving all the details so please bear with me through to the end.
I'm working against a legacy database over which I do not have much control. I want to be able to map a class to multiple database tables. Here is how my tables look
Lookup
+--------+--------------+------------+
| Column | DataType | Attributes |
+--------+--------------+------------+
| Id | INT | PK |
| Code | NVARCHAR(50) | |
+--------+--------------+------------+
Culture
+--------------+--------------+------------+
| Column | DataType | Attributes |
+--------------+--------------+------------+
| Id | INT | PK |
| Culture_Code | NVARCHAR(10) | |
+--------------+--------------+------------+
Lookup_t9n
+----------------+---------------+---------------------+
| Column | DataType | Attributes |
+----------------+---------------+---------------------+
| Id | INT | PK |
| Culture_Id | INT | FK to Culture table |
| Localised_Text | NVARCHAR(MAX) | |
+----------------+---------------+---------------------+
As you can see, I have a lookup table where all lookups are stored. The display text for a lookup is localized and stored in a separate table. This table has a foreign key to culture table to indicate the culture for which the localized text exists.
My class looks like this
public class Lookup {
public virtual int Id {get; set;}
public virtual string Code {get; set;}
public virtual string DisplayText {get; set;}
}
And my FNH mapping class looks like this
public class LookupMappings : ClassMap<Lookup> {
public LookupMappings()
{
Table("Lookup");
Id(x => x.Id).Column("Id");
Map(x => x.Code).Column("Code");
Join("Lookup_t9n", join => {
join.Map(x => x.DisplayText).Column("Localised_Text"); //Note this place, my problem is here
})
}
}
In the above mapping, in Join part I want to provide some where clause like WHERE Lookup_t9n.Culture_Id = Culture.Culture_Id AND Culture.Culture_Code = System.Threading.Thread.CurrentUICulture.CultureCode.
I know this is not a valid SQL but conveys the intent I hope. Has anyone have any experience of doing such a thing.
I can add a mapping layer where I can have classes that map one-to-one with database tables and then write plain c# to map those classes back to my Lookup class. I have rather done that as an interim solution. I was wondering if I can remove that mapping layer with some smart NH use.

Answer 1

I do not have simple answer, like CallThis(). I would like to give you suggestion, based on how we are using similar stuff. The solution is base on the standard mapping, hidding its complexity in C# Entities. It is just a draft of the solution so I'll skip the middle Culture table, and will expect that in Lookup_t9n we do store just a culture name (en, cs...)
Let's have this class
public class Lookup {
public virtual int Id {get; set;}
public virtual string Code {get; set;}
// for simplicity skipping null checks
public virtual DisplayText { get { return Localizations.First().LocalizedText; } }
public virtual IList<Localization> Localizations {get; set;}
}
public class Localization { // mapped to Lookup_t9n
public virtual string CultureName {get; set;}
public virtual string LocalizedText {get; set;}
}
Having this, we can map the collection of Localizations as HasMany. It could even be mapped as a component (see example of component mapping)
Now, what we do need is to introduce a filter. Example with Fluent. The essential documentation: 18.1. NHibernate filters.
Simplified mapping
filter:
public class CulturFilter : FilterDefinition
{
public CulturFilter()
{
WithName("CulturFilter")
.AddParameter("culture",NHibernate.NHibernateUtil.String);
}
collection:
HasMany(x => x.Localization)
.KeyColumn("Id")
...
.ApplyFilter<CulturFilter>("CultureName = :culture"))
.Cascade.AllDeleteOrphan();
Finally, we have to introduce some AOP filter, IInterceptor... which will be triggered each time (needed) and adjust the ISession
session
.EnableFilter("CulturFilter")
.SetParameter("culture"
,System.Globalization.CultureInfo.CurrentCulture.TwoLetterISOLanguageName);
And now we have Localized string based on current culture, while using standard mapping of localized values as a collection.