Comments on: Aggregated specifications

By: Matt

Matt — Fri, 28 May 2010 14:37:18 +0000

The entity

By: peter

peter — Fri, 28 May 2010 14:33:23 +0000

Hi!
So in this method…
public Product[] Search(IProductSearchQuery query)
{
var products = _session.Linq();
return _filters
.Where(x => x.ShouldApply(query))
.Aggregate(products, (candidates, filter) =>
filter.Filter(candidates, query)).ToArray();
}

You are tying yourself to the ENTITY Product or is that an IProduct? If its an implementation of IProduct, why not return IProduct[]
Thanks

By: Jeff Doolittle

Jeff Doolittle — Fri, 16 Oct 2009 06:55:17 +0000

Matt,

Thanks for this post. We’ve put Fluent NHibernate + LINQ-To-NHibernate + StructureMap + Aggregated Specifications to use on our current project with great success so far. The power of aggregated specifications with LINQ is incredible. The expressiveness without loss of testability has been a huge win for our team.

–Jeff

By: Samuel Jack

Samuel Jack — Fri, 09 Oct 2009 08:44:34 +0000

Matt,
Of course – should have thought of that! Nice article, by the way.

By: Luca

Luca — Thu, 08 Oct 2009 16:28:06 +0000

Very good article!

By: Matt

Matt — Thu, 08 Oct 2009 16:00:43 +0000

No, you just do a regular state-based test on the return value using AsQueryable and ToArray, etc. The following code isn't a good test. This example is descriptive NOT prescriptive:

[Test]
public void Should_filter_products_in_range()
{
	var query = MockRepository.GenerateStub();
	query.Price = 6m;
	query.PriceRange = 3;

	var product1 = new Product {Price = 1m};
	var product2 = new Product {Price = 5m};
	var product3 = new Product {Price = 10m};

	var filter = new PriceRangeFilter();

	IQueryable candidates = new[]{product1, product2, product3}.AsQueryable();

	var products = filter.Filter(candidates, query).ToArray();

	Assert.That(products.Length, Is.EqualTo(1));
	Assert.That(products[0], Is.SameAs(product2));
}

By: Samuel Jack

Samuel Jack — Thu, 08 Oct 2009 15:36:56 +0000

Matt,
When you say you can test drive PriceRangeFilter, I can see how you test ShouldApply, but how do you test the Filter method? Surely that would mean unpicking the IQueryable to find out what criteria had been added to it?