Will Beattie's Blog

  Firstly just to clarify I am going to be talking about the OOP Specification Pattern not the data pattern commonly found in the SID (Shared Information & Data) model. Much has been said about the specification pattern so I’m not going to go into that, if you want an overview check out these posts: http://www.lostechies.com/blogs/chrismissal/archive/2009/09/10/using-the-specification-pattern-for-querying.aspx http://devlicio.us/blogs/jeff_perrin/archive/2006/12/13/the-specification-pattern.aspx In this post I’m going to demonstrate how you can make use of the specification pattern to query Entity Framework and create reusable, testable query objects and eliminate inline LINQ queries. The Smell When I first got started with Entity Framework way back in 2008 when EF was still in it’s infancy we had lot’s of inline LINQ all over the code base and specific methods on our repositories for querying requirements (which any OOP purist will tell you is bad). We had ...

Recently I had an Advanced Search requirement which had to enable Users to specify a combination of fields to search for and the operator e.g. AND, OR and the type of comparison to do e.g. LIKE, EQUALS. The DataLayer is built upon the Entity Framework and I'm using LINQ to Entities as the query mechanism. So my overriding goal was to keep this Strongly Typed but maintainable as well. Firstly I created a generic SearchInfo object of which there would be one for each field that needed to be included in the search. public class SearchInfo<T> { public Expression<Func<T, object>> PropertySelector { get; set; } public QueryOperator Operator { get; set; } public StringComparer Comparer { get; set; } public string Value { get; set; } } public enum QueryOperator { And = 0, Or = 1 } public enum StringComparer { Equals = 0, StartsWith = 1, EndsWith = 2, Contains = 3 } Now if we just had to deal with the AND operator we could achieve this by con...