TechNet Express: How to Implement Language Translation in WCF Data Service (OData) Part-1

Language translation in WCF Data Service can be handled in two ways. First by using Entity Level Join in QueryView and second is by using ObjectMaterialized event provided by DataService class.

This article covers first part (QueryView ) and works well for one table (It can works for multiple translation table if translation table has all the required translation entries)

But I would suggest to use this approach only when if there is only one translation table. For multiple translation table please refer to Part2 of this article.

Download Code Sample

Alternative Title

Implementing Language Sensitive Response in WCF Data Service .

Multilingual Support in WCF Data Service

Culture Negotiation in WCF Data service

Problem
You are developing a data service for international customer and need to provide language specific translation for some fields (properties/columns)

Use Case

you have a master product table that contains a ProductName column. Also there is a Translation table that provides product names in different languages. Now we need to build a web service that provides Product Name and It`s translated name side by side as a single entity based on language code supplied by user or system.

Discussion
There are two fundamentals approach for displaying multilingual data in a web service.

Super Imposition : In this approach either standard (say en-us) or translated (say IT-IT) content is delivered.This technique create smaller pay load than next one discussed. Also in this approach schema of the Entity that represent database table is unchanged.
Parallel Imposition or Side By Side approach: In this approach we add on extra property for each property that require translation. The extra property provides translated value.

<m:properties>

<d:ProductID m:type="Edm.Int32">1</d:ProductID>

<d:ProductName>Chai</d:ProductName>

<d:ProductTranslatedName>IT_Chai</d:ProductTranslatedName>

<d:SupplierID m:type="Edm.Int32">1</d:SupplierID>

....

</m:properties>

Solution

High level solution is listed below

Expose your Data Table(Ex Products) and Translation Table (Ex NameTranslation) as entity in your EDMX
Add two scalar property (Translated Name and Language) in your Entity (Product) generated by EDMX
Create a Left outer join of Data Entity (Product) and Translation Entity (ThanslatedName) based on primary key of Product Table using Query View of Mapping section in EDMX

Handling Language Parameter
Note :- This Article do not cover "Language Parameter Handling " and code sample uses hard coded language parameter to simplify demonstration
There could me multiple ways to receive language parameter in the WCF data processing pipeline.

Query Interceptor : Refer to http://ashwini47-tts.blogspot.com/2012/03/how-to-parametrized-queryinterceptor-in.html
Request Header that can be obtained by DataServiceOperationContext Supplied in OnStartProcessingRequest function as argument.
Reading browser capabilities via DataServiceOperationContext. Most of the real life application uses this approach.

Attached Solution

Uses Northwind database and exposed tow tabled Products and Name Translation as entity in edmx.
Two additional properties are added in entity conceptual model as below

I had created a table called NameTranslation that simulate translations just two products and two languages EN and IT and exposed as entity.
Mapping of Product entity is modified to implement Left outer join with Translation table. This technique discard existing scalar mapping and uses query based mapping abs below.

select value

NORTHWNDModel.Product

(p.ProductID,

p.ProductName,

case when t.ProductNativeName is null then 'Translation Not Found'

else t.ProductNativeName

end,

p.SupplierID,

p.CategoryID,

p.QuantityPerUnit,

p.UnitPrice,

p.UnitsInStock,

p.UnitsOnOrder,

p.ReorderLevel,

p.Discontinued,

case when t.Language is null then 'N/A'

else t.Language

end )

from NORTHWNDModelStoreContainer.Products as p

left join NORTHWNDModelStoreContainer.NameTranslation as t

on p.ProductID=t.ProductID

</QueryView>

<!--<EntityTypeMapping TypeName="NORTHWNDModel.Product">

</MappingFragment>

</EntityTypeMapping>-->

</EntitySetMapping>

This completes edmx manipulation and now we need to write a Query Interceptor in Data Service class that can intercept the request and filter the response based on Language requested.

[QueryInterceptor("Products")]

public Expression<Func<Product, bool>> OnQueryOrders()

{

//This code uses hardecoded language parameter but if you want to pass it

// dynamicly use query paramteters

// see http://ashwini47-tts.blogspot.in/2012/03/how-to-parametrized-queryinterceptor-in.html

string language = "IT-IT";

string P = this.CurrentDataSource.Products.ToTraceString();

return o => (o.Language == language || o.Language == "N/A");

}

This completes the code base and service is ready to test. Try navigating the entity set (http://localhost:11002/WcfDataService1.svc/Products) belwo is the output.

<m:properties>

<d:ProductID m:type="Edm.Int32">2</d:ProductID>

<d:ProductName>Chang</d:ProductName>

<d:ProductTranslatedName xml:space="preserve">IT_Chang</d:ProductTranslatedName>

<d:SupplierID m:type="Edm.Int32">1</d:SupplierID>

<d:CategoryID m:type="Edm.Int32">1</d:CategoryID>

<d:QuantityPerUnit>24 - 12 oz bottles</d:QuantityPerUnit>

<d:UnitPrice m:type="Edm.Decimal">19.0000</d:UnitPrice>

<d:UnitsInStock m:type="Edm.Int16">17</d:UnitsInStock>

<d:UnitsOnOrder m:type="Edm.Int16">40</d:UnitsOnOrder>

<d:ReorderLevel m:type="Edm.Int16">25</d:ReorderLevel>

<d:Discontinued m:type="Edm.Boolean">false</d:Discontinued>

<d:Language>IT-IT</d:Language>

</m:properties>

Further References

15-2. Mapping an Entity to Customized Parts of One or More Tables of Entity Framework 4.0 Recipes, Larry Tenny and Zeeshan Hirani (APress)
QueryView Element (MSL)

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Saturday, March 24, 2012

How to Implement Language Translation in WCF Data Service (OData) Part-1

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