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aggregatable.md

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uid title product categories summary
aggregatable
Parent/Child, Visitor and Disposable
postsharp
PostSharp;AOP;Metaprogramming
The document discusses the concept of parent-child relationship in object-oriented design, its implementation in PostSharp, and the three types of object relationships in UML specification: Aggregation, Composition, and Association.

Parent/Child, Visitor and Disposable

The parent-child relationship is a foundational concept of object oriented design. There are three kinds of object relationships in the UML specification:

  • Aggregation is the parent-child (also named whole-part) relationship. It is implemented in PostSharp by the xref:PostSharp.Patterns.Model.AggregatableAttribute aspect described in xref:aggregatable-adding.

  • Composition is an aggregation relationship where the parent controls the lifetime their children. It is implemented in PostSharp by the xref:PostSharp.Patterns.Model.DisposableAttribute aspect pattern, which relies on the xref:PostSharp.Patterns.Model.AggregatableAttribute aspect. For details, see xref:disposable.

  • Association is a simple reference between two objects.

Despite its importance, C# and VB have no keyword to represent aggregation. All C# and VB object references correspond to an association. Therefore, most applications and frameworks tend to re-implement the aggregation relationship, resulting in boilerplate code and defects. For instance, UI frameworks such as WinForms and WPF rely on a parent-child structure.

PostSharp implements the Aggregatable pattern thanks to the xref:PostSharp.Patterns.Model.AggregatableAttribute aspect, together with the xref:PostSharp.Patterns.Model.ChildAttribute, xref:PostSharp.Patterns.Model.ReferenceAttribute and xref:PostSharp.Patterns.Model.ParentAttribute custom attributes.

The Aggregatable pattern is used by other PostSharp aspects, including all threading models (xref:PostSharp.Patterns.Threading.ThreadAwareAttribute), xref:PostSharp.Patterns.Model.DisposableAttribute and xref:PostSharp.Patterns.Recording.RecordableAttribute. You can also use the aspect to automatically implement a parent-child relationship in your own code.

In this chapter

Section Description
xref:aggregatable-adding This section shows how to prepare a class so that it can participate in a parent-child relationship.
xref:aggregatable-visitor This section describes how to enumerate the children of an object thanks to the visitor pattern.
xref:disposable This section shows how to automatically implement the xref:System.IDisposable interface so that children objects are disposed when the parent object is disposed.
xref:advisable-collections This section covers advanced topics related to collections in aggregatable object models.