Session: Querying: How to use transformers in queries?

Transformers can be used with session queries using TransformWith method.

Syntax

IRavenQueryable<TResult> TransformWith<TTransformer, TResult>()
where TTransformer : AbstractTransformerCreationTask, new();

IRavenQueryable<TResult> TransformWith<TResult>(string transformerName);

Parameters
transformerName	string	Name of a transformer to use.

Return Value
IRavenQueryable	Instance implementing IRavenQueryable interface containing additional query methods and extensions.

Example I

// return up to 128 entities from 'Products' collection
// transform results using 'Products_Name' transformer
// which returns only 'Name' property, rest will be 'null'
List<Product> results = session
.Query<Product>()
.Where(x => x.Name == "Chocolade")
.TransformWith<Products_Name, Product>()
.ToList();

Example II

Loading document inside transformer and projecting results to different type.

public class ProductWithCategoryAndSupplier
{
public string Name { get; set; }

public Supplier Supplier { get; set; }

public Category Category { get; set; }
}

public class Products_WithCategoryAndSupplier : AbstractTransformerCreationTask<Product>
{
public Products_WithCategoryAndSupplier()
{
	TransformResults =
		products => from product in products 
					select new
					{
						Name = product.Name,
						Category = LoadDocument<Category>(product.Category),
						Supplier = LoadDocument<Supplier>(product.Supplier)
					};
}
}

// return 1 entity from 'Products' collection
// transform results using 'Products_WithCategoryAndSupplier' transformer
// project results to 'ProductWithCategoryAndSupplier' class
ProductWithCategoryAndSupplier product = session
.Query<Product>()
.Where(x => x.Name == "Chocolade")
.TransformWith<Products_WithCategoryAndSupplier, ProductWithCategoryAndSupplier>()
.First();

Assert.Equal("Chocolade", product.Name);
Assert.Equal("Confections", product.Category.Name);
Assert.Equal("Zaanse Snoepfabriek", product.Supplier.Name);