How to Create Specifications

Create your specification by inheriting from Specification<T>, and use the Query builder in the constructor to define your conditions.

public class CustomerSpec : Specification<Customer>
{
    public CustomerSpec(int age)
    {
        Query.Where(x => x.Age > age)
             .Include(x => x.Addresses)
             .OrderBy(x => x.FirstName);
    }
}

Single Result Specification

The library exposes an ISingleResultSpecification<T> marker interface. We also define a SingleResultSpecification<T> base class as a convenience.

public class SingleResultSpecification<T> : Specification<T>, ISingleResultSpecification<T>
{
}

Create your specification by inheriting from SingleResultSpecification<T>.

public class CustomerByIdSpec : SingleResultSpecification<Customer>
{
    public CustomerByIdSpec(int id)
    {
        Query.Where(c => c.Id == id);
    }
}

The ISingleResultSpecification<T> and SingleResultSpecification<T> are functionally dormant. They act just as a marker and the consumers may utilize them to further clarify the intent of the given specification. For instance, Single or SingleOrDefault repository methods are constrained to accept only single result specifications.

Projection Specification

The specification can be used to project the result into a different type. Inherit from Specification<T, TResult> base class, where TResult is the type you want to project into. This offers strongly typed experience in the builder and during the evaluation.

public class CustomerSpec : Specification<Customer, CustomerDto>
{
    public CustomerSpec(int age)
    {
        Query.Where(x => x.Age > age)
             .OrderBy(x => x.FirstName)
             .Select(x => new CustomerDto(x.Id, x.Name));
    }
}

From here, additional operators can be used to further refine the Specification. These operators follow LINQ syntax and are described in more detail in the Features section.