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Specification

Base class with tests for adding specifications to a DDD model. Also includes a default generic Repository base class with support for EF6 and EF Core. Currently used in Microsoft reference application eShopOnWeb, which is the best place to see it in action, as well as the Clean Architecture solution template. Check out Steve "ardalis" Smith's associated (free!) eBook, Architecting Modern Web Applications with ASP.NET Core and Azure, as well.

Documentation

Read the Documentation

Videos

🎥 Watch What's New in v5 of Ardalis.Specification

🎥 Watch an Overview of the Pattern and this Package

Version 6 Release Notes

Breaking changes

• Improve in-memory evaluation performance. #182. Breaking Changes: The specification state for Where, Order, and Search expressions is stored in separate types.

• Remove Paginate builder action. Breaking Change (It was marked as obsolete since version 4). Issue #189

Other updates

• Add support for AnyAsync in the base repository. #180

• Add SQL Like implementation for the in-memory evaluator. #150

• Add support for IgnoreQueryFilters. #159

• Return Task<int> from SaveChangesAsync. #174

• Add support for condition in the specification builder methods. #143

• Improve Include evaluation performance by implementing caching (opt-in feature). Issue #187

• Implement infrastructure for specification validators. Issue #111

• GetBySpecAsync and similar methods are marked obsolete; prefer FirstOrDefault or SingleOrDefault instead.

Sample Usage

The Specification pattern pulls query-specific logic out of other places in the application where it currently exists. For applications with minimal abstraction that use EF Core directly, the specification will eliminate Where, Include, Select and similar expressions from almost all places where they're being used. In applications that abstract database query logic behind a Repository abstraction, the specification will typically eliminate the need for many custom Repository implementation classes as well as custom query methods on Repository implementations. Instead of many different ways to filter and shape data using various methods, the same capability is achieved with few core methods.

Example implementation in your repository using specifications

public async Task<List<T>> ListAsync(ISpecification<T> specification, CancellationToken cancellationToken = default)
{
	return await ApplySpecification(specification).ToListAsync(cancellationToken);
}

private IQueryable<T> ApplySpecification(ISpecification<T> specification)
{
	return SpecificationEvaluator.Default.GetQuery(dbContext.Set<T>().AsQueryable(), specification);
}

Now to use this method, the calling code simply instantiates and passes the appropriate specification.

var spec = new CustomerByNameSpec("customerName");
var customers = await _repository.ListAsync(spec, cancellationToken);

Specifications should be defined in an easily-discovered location in the application, so developers can easily reuse them. The use of this pattern helps to eliminate many commonly duplicated lambda expressions in applications, reducing bugs associated with this duplication.

We're shipping a built-in repository implementation RepositoryBase, ready to be consumed in your apps. You can use it as a reference and create your own custom repository implementation.

Running the tests

This project needs a database to test, since a lot of the tests validate that a specification is translated from LINQ to SQL by EF Core. To run the tests, we're using docker containers, including a docker-hosted SQL Server instance. You run the tests by simply running RunTests.bat or RunTests.sh.

Reference

Some free video streams in which this package has been developed and discussed on YouTube.com/ardalis.

• Reviewing the Specification Pattern and NuGet Package with guest Fiseni 6 Nov 2020
• Open Source .NET Development with Specification and Other Projects 14 Jan 2020
• Updating Specification and GuardClauses Nuget Packages / GitHub Samples 20 Nov 2019
• Ardalis - Working on the Ardalis.Specification and EF Extensions GitHub projects 16 Aug 2019
• Working on the Ardalis.Specification Nuget Package and Integration Tests 23 July 2019

Pluralsight resources:

• Design Patterns Library - Specification
• Domain-Driven Design Fundamentals
• Specification Pattern in C#