Specification Pattern - Example of Use

Example of Use

In the following example, we are retrieving invoices and sending them to a collection agency if they are overdue, notices have been sent and 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 OverdueSpecification class that is satisfied when an invoice's due date is 30 days or older, a NoticeSentSpecification class that is satisfied when three notices have been sent to the customer, and an InCollectionSpecification 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 SendToCollection 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.

OverDueSpecification OverDue = new OverDueSpecification; NoticeSentSpecification NoticeSent = new NoticeSentSpecification; InCollectionSpecification InCollection = new InCollectionSpecification; // example of specification pattern logic chaining ISpecification SendToCollection = OverDue.And(NoticeSent).And(InCollection.Not); InvoiceCollection = Service.GetInvoices; foreach (Invoice currentInvoice in InvoiceCollection) { if (SendToCollection.IsSatisfiedBy(currentInvoice)) { currentInvoice.SendToCollection; } }