Specification pattern: Difference between revisions

Revision as of 11:53, 25 April 2023

Revision as of 02:22, 21 April 2024

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In computer programming, the '''specification pattern''' is a particular [[software design pattern]], whereby [[business rules]] can be recombined by chaining the business rules together using [[boolean algebra|boolean logic]]. The pattern is frequently used in the context of [[___domain-driven design]].

A specification pattern outlines a business rule that is combinable with other business rules. In this pattern, a unit of business logic inherits its functionality from the abstract aggregate Composite Specification class. The Composite Specification class has one function called IsSatisfiedBy that returns a boolean value. After instantiation, the specification is "chained" with other specifications, making new specifications easily maintainable, yet highly customizable business logic. Furthermore, upon instantiation the business logic may, through method invocation or [[inversion of control]], have its state altered in order to become a delegate of other classes such as a persistence repository.

As a consequence of performing runtime composition of high-level business/___domain logic, the Specification pattern is a convenient tool for converting ad-hoc user search criteria into low level logic to be processed by repositories.

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# they are not already with the collection agency.

This example is meant to show the end result of how the logic is 'chained' together.

This usage example assumes a previously defined <code>OverdueSpecification</code> class that is satisfied when an invoice's due date is 30 days or older, a <code>NoticeSentSpecification</code> class that is satisfied when three notices have been sent to the customer, and an <code>InCollectionSpecification</code> class that is satisfied when an invoice has already been sent to the collection agency. The implementation of these classes isn't important here.

Using these three specifications, we created a new specification called <code>SendToCollection</code> which will be satisfied when an invoice is overdue, when notices have been sent to the customer, and are not already with the collection agency.