Question

What is the best way to design the Domain objects which can have multi-lingual fields. An example can be a Product class with Description being multi-lingual.

I have found few links but could not decide which one is the best way.

1. http://fabiomaulo.blogspot.com/2009/06/localized-property-with-nhibernate.html
   (This stores all localised language data in one field. Can be a problem if we query from Sql)

2. http://ayende.com/Blog/archive/2006/12/26/LocalizingNHibernateContextualParameters.aspx
   (This one has a warning at the beginning that it is a hack and no longer supported)

3. http://www.webdevbros.net/2009/06/24/create-a-multi-languaged-domain-model-with-nhibernate-and-c/
   (This does not describe how multilingual data will be structured in the database.)

Anyone having experience with using NHibernate with multi-lingual data. Is there a better way?

Answer 1

The third option looks great. The hibernate mapping is given, but not the database schema – if that’s what you are missing, then I’ll sketch it out here:

dictionary
----------
ID: int - identity
name: nvarchar(255)

phrase
------
dictionary_id:int  (fkey dictionary.ID)
culture_id:int     (LCID)
phrase:nvarchar(255)  - this is the default size - seems too small

According to this blog entry, 255 is the default string length for String values. To overcome the short string length on the phrase text, you can change the <element> tag to

<element column="phrase" type="String" length="4001"></element>

To use this in your domain model, you add a PhraseDictionary property to your entity where you want translatable text. E.g. the title property or decription property.

I think the article describes a great approach, and is the one that I would go
for.

EDIT: In response to the comments, make the length less than 4001 if you know the absolute maximum size is less than that, as this will typically be faster. Also, NHibernate will lazily fetch the collection, but it may fetch all the items at once. You can profile to determine if this has any performance implications. (If you have only a handful of languages then I doubt you will see a difference.) If you have many languages (Say 50+) then it may be worthwhile creating custom properties to fetch the localized text. These will issue queries to fetch specifically the text required. More importantly, you may be able to fetch all the text for a given entity in one query, rather than each localized text property as a separate query.

Note that this extra effort is only needed if profiling gives you reason to be concerned about the performance. Chances are that the implementation in the article as is will function more than adequately.