peschuster / PropertyTranslator

PropertyTranslator

Translates computed properties in LINQ queries into their implementation (based on Microsoft.Linq.Translations).

What does it?

PropertyTranslator exchanges properties in linq queries before execution. This is especially useful if the underlying LINQ provider does not support some kind of operation or you want to add client-side calculations in your business logic to e.g. an EntityFramework model.

For a general introduction into the topic, have a look at this blog post. PropertyTranslator actually is a enhancement of the presented solution in the post.

For an introduction specifically to PropertyTranslator have a look at these two blog posts: LINQ: How to dynamically map properties and PropertyTranslator and Interfaces

What's the difference to Linq.Translations?

PropertyTranslator plays well together with QueryInterceptor and thus can be added to every query in some kind of "data context" or general table / ObjectSet provider.

Furthermore it internally adds one more layer of abstraction to allow property translation depending on the ui culture of the current thread.

Examples

Basic example

A POCO entity class from EntityFramework. Although in the database only a FirstName and a LastName field exists, the property Name can be used in queries, because right before execution of the query it is translated to FirstName + ' ' + LastName.

public class Person
{
	private static readonly CompiledExpressionMap<Person, string> fullNameExpression = 
	    DefaultTranslationOf<Person>.Property(p => p.FullName).Is(p => p.FirstName + " " + p.LastName);
	    
	public string FullName
	{
		get { return fullNameExpression.Evaluate(this); }
	}
	
	public string FirstName { get; set; }
	
	public string LastName { get; set; }    	
}

A more advanced example with ui culture dependent translations

The context: a database table, mapped with entity framework to POCO entity classes with two fields: EnglishName and GermanName. With the following snippet, you can use the Name property in linq queries which resolves to the name (either EnglishName or GermanName) depending on the current ui culture.

public class Country
{
	private static readonly CompiledExpressionMap<Country, string> nameExpression = 
	    DefaultTranslationOf<Country>.Property(c => c.Name).Is(c => c.EnglishName);
	
	static Country()
	{
	    DefaultTranslationOf<Country>.Property(c => c.Name).Is(c => c.EnglishName, 'en');
	    DefaultTranslationOf<Country>.Property(c => c.Name).Is(c => c.GermanName, 'de');
	}    	
	
	public string Name
	{
		get { return nameExpression.Evaluate(this); }
	}
	
	public string EnglishName { get; set; }
	
	public string GermanName { get; set; }    	
}

How to enable PropertyTranslator

You can enable PropertyTranslator by adding the PropertyVisitor to your EntityFramework ObjectSets (of course it works not only with EntityFramework but with any LINQ provider):

using QueryInterceptor;
using PropertyTranslator;

public class MyDataContext
{
    ObjectContext context = new MyEfContext();
    
    public IQueryable<Person> PersonTable
    {
        get
        {
            var objectSet = context.CreateObjectSet<Person>("Persons");
            
            return objectSet.InterceptWith(new PropertyVisitor());
        }
    }
}

How to use it

PropertyTranslator is on Nuget: http://nuget.org/packages/Linq.PropertyTranslator I'd recommend to use it together with QueryInterceptor by David Fowler.