Implementation of specification pattern for usage with ORM (currently NHiberante and ef.core are supported)

Add reference to nuget package in your domain layer project

Install-Package Singularis.Specification.Definition

Add reference to nuget package in your data access layer project: For ef.core use:

Install-Package Singularis.Specification.Executor.EntityFramework

For NHibernate use:

Install-Package Singularis.Specification.Executor.Nhibernate

Create a rule (aka specification) in the domain layer. All the rules must be derived from Specification class and must initialize Query property in ctor:

public class CreatedAfter: Specification<User>
{
  public CreatedAfter(DateTime date)
  {
     Query = Source().Where(x => x.CreatedAd > date);
  }
}

Use the rule with repository:

var repository = serviceProvider.GetRequiredService<IRepository<int>>();
var newUsers = repository.List(new CreatedAfter(new DateTime(2020, 1, 1));

You can build a complex rule based on existsing ones using two extension methods: Combine() and Or(). Combine appends one rule to another. The rule can contains any operation. Or can contains only Where operation.

You can read more info about library in the on habr.com (in russian): https://habr.com/ru/company/singularis/blog/485328/