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Specification pattern implementation in C#

This repository provides a C# Composite based implementation ofthe Specification pattern.

The Composite implementation adds flexibility by allowing thebusiness rules to be combined. In additional to the logicaloperations, this implementation uses a Builder pattern withFluent Interfaces. As a result, we can use extensions methods,instead of classes, to create new rules.

The examples below compares the standard composite implementationto an implementation using the builder and fluent interfaces.

In a standard implementation, the rule definition is located insidethe class:

publicclassBlogCreatedAfterSpecification:BaseSpecification<Blog>{publicBlogCreatedAfterSpecification(DateTimedateTime):base(x=>x.Created>=dateTime){}}

This is how to instantiate and build the specifications:

varcreatedAfter=newBlogCreatedAfterSpecification(dateTime);varnotBanned=newBlogNotBannedSpecification();varnotExpired=newBlogNotExpiredSpecification();varspecification=createdAfter.And(notBanned).And(notExpired);

Instead of a class per rule, a extension method is used to add rules.In the sample code below, Add is a method with an Expression parameter,it create an instance of the Specification and add to the compositestructure.

publicstaticclassBlogSpecificationExtensions{publicstaticISpecification<Blog>CreatedAfter(thisISpecification<Blog>specification,DateTimedateTime){returnspecification.And(x=>x.Created>=dateTime);}}

The composed rule can be instantiated like below. The result is thatthe business rules can be read more fluently.

varspecification=SpecificationBuilder<Blog>.Create().CreatedAfter(dateTime).NotBanned().NotExpired();

dotnet core >= 2.0

This repository provides a console application in additional to an xUnitand a Specflow test project.Please note that Specflow project only worksin Windows environment.

Running the console application:

cd src/SpecificationDemodotnet ef migrations add InitialCreate --startup-project ../SpecificationDemoConsoledotnet ef database update --startup-project ../SpecificationDemoConsoledotnet run

Running tests:

dotnettest SpecificationDemoXunitTestdotnettest SpecificationDemoBddTest

Requirements:

LinqPad >= 5.26Entity Framework 7 (EF Core) Driver >= 2.0.1

Before configuring the connection, you need to publish one project:

cd src/SpecificationDemoConsoledotnet publish

Then configure the connection following the steps below:

• Add a new connection
  • Use a typed data context using Entity Framework 2.0.1
  • In thePath to custom assembly, select the publish directory. Example:D:\dotnet-specification-pattern\src\SpecificationDemoConsole\bin\Debug\netcoreapp2.0\SpecificationDemo.dll
  • Select theFull type name of the typed DbContext: SpecificationDemo.Data.BloggingContext
  • SelectVia a constructor that accepts a string:Server=(localdb)\mssqllocaldb;Database=Blog;Trusted_Connection=True;ConnectRetryCount=0
  • SelectRemember this connection

Create a new query and change toC# Program. Then, select theBloggingContext in SpecificationDemo.dll connection.

Inquery properties (F4), add the following namespaces:

SpecificationDemo.DataSpecificationDemo.EntitiesSpecificationDemo.SpecificationsSystemSystem.DataSystem.LinqSystem.Threading.Tasks

LinqPadC# Program sample code :

voidMain(){varblogRepository=newEfReadRepository<Blog>(this);varspecification=SpecificationBuilder<Blog>.Create().NotExpired().CreatedAfter(newDateTime(2017,1,1));varresult=blogRepository.Where(specification, b=>b.Posts).ToList();Console.WriteLine(result);}

UsingC# Statement(s) this can be simplified to:

varspecification=SpecificationBuilder<Blog>.Create().NotExpired().CreatedAfter(newDateTime(2017,1,1));Console.Write(Blogs.Where(specification));

Copyright (c) 2018 André Gomes

Licensed under theMIT License.