/Specification

Base class with tests for adding specifications to a DDD model

Primary LanguageC#MIT LicenseMIT

NuGetNuGet Actions Status

NuGet: Ardalis.Specification

Specification

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

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 just this code:

public async Task<IReadOnlyList<T>> ListAsync(ISpecification<T> spec)
{
  var specificationResult = await ApplySpecification(spec);
  return await specificationResult.ToListAsync();
}
private async Task<IQueryable<T>> ApplySpecification(ISpecification<T> spec)
{
  return await EfSpecificationEvaluator<T>.GetQuery(_dbContext.Set<T>().AsQueryable(), spec);
}

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

Reference

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

Pluralsight resources: