The specification example is a way to expose the interface of a single specification while at the same time has the ability to keep a list of many specifications. This pattern can be used with the 'and' operator, or the 'or' operator.
NOTE: The example is difficult to follow for re-creation. So for now I only have some general notes on this type of composite pattern use case. Also, I would like to note for future reference that the specification pattern is stated to be an 'enterprise pattern' in this lesson.
-
ISpecification
- An abstract class which contains an abstract IsSatisfied method. It provides '& 'operator behavior in use with the ISpecification type and returns a new AndSpecification.
-
CompositeSpecification
- An abstract class which extends the ISpecification. It stores a list of ISpecifications. It exposes the interface of a single object ( Scalar ) while at the same time is not really a single object ( Composition ) because it keeps a list of specifications.
-
AndSpecification
- Extends CompositeSpecification and takes a generic parameter of type T. The AndSpecification constructor passes params to the base class ( CompositeSpecification ) to store them in a list. In addition, it contains an IsSatisfied override method which checks all the items in the list of the base class against a parameter of the same type. The AndSpecification is typically called a 'combinator' which combines things together for the 'and' operator. This can be modified to use the 'or' operator.
Design Patterns in C# and .NET - Composite: Specification
