Specifications can be build by Fluent API or by normal constructors, because all built-in Specifications are public to use.

Constructors

Built-in Specifications are available in two namespaces:

• FluentSpecification.Core.Composite - core Specifications for composition (like And, Or etc.).
• FluentSpecification.Common - other common Specifications (like Empty, Equal, Null etc.).

var trueSpec = new TrueSpecification();
var emptyStringSpec = new EmptySpecification<string>();

// Create 'Customer' specification for 'IsActive' property and use TrueSpecification -
// 'IsActive' must be true
var activeSpec = new PropertySpecification<Customer, bool>(
    c => c.IsActive, trueSpec);
// Create 'Customer' specification for 'Comments' property and use EmptySpecification -
// 'Comments' must be null or string.Empty
var commentsSpec = new PropertySpecification<Customer, string>(
    c => c.Comments, emptyStringSpec);

// Compose previous 'Customer' specifications
var andSpec = new AndSpecification<Customer>(activeSpec, commentsSpec);

Fluent API

All built-in Specifications have set of extensions for ISpecification<T> interface, and can be used fluently.

var trueSpec = new TrueSpecification();
var notEmptyStringSpec = new EmptySpecification<string>()
    .Not();

// Create 'Customer' specification for 'IsActive' property and use TrueSpecification -
// 'IsActive' must be true
var activeSpec = new PropertySpecification<Customer, bool>(
    c => c.IsActive, trueSpec);
// Create 'Customer' specification for 'Comments' property and use EmptySpecification -
// 'Comments' must be NOT null or NOT string.Empty
var commentsSpec = new PropertySpecification<Customer, string>(
    c => c.Comments, notEmptyStringSpec);

// Compose previous 'Customer' specifications
var andSpec = activeSpec
    .And(commentsSpec);

Entry point

To prevent use constructors, there is a special static class Specification in FluentSpecification namespaces, and this is formall "entry point".
Specification contains creation methods for all built-in Specifications and also negations for some of them.

// Previous examples in flatten version
var finalSpec = Specification
    .True<Customer>(c => c.IsActive)
    .And()
    .NotEmpty(c => c.Comments);