Composite Entity Pattern

1. Introduction

The Composite Entity Pattern is a structural design pattern that allows you to compose objects into tree structures to represent part-whole hierarchies. This pattern allows clients to work with individual objects and compositions uniformly.

2. Key Concepts

3. Structure

The Composite Entity Pattern typically involves the following components:

• Component: The interface or abstract class defining the common interface for all concrete components.
• Composite: A class that implements the Component interface and holds children components.
• Leaf: A class that implements the Component interface and represents leaf nodes in the composition.

4. Implementation

Here’s an example implementation of the Composite Entity Pattern in Python:

class Component:
    def operation(self):
        pass

class Leaf(Component):
    def operation(self):
        return "Leaf"

class Composite(Component):
    def __init__(self):
        self.children = []

    def add(self, component):
        self.children.append(component)

    def operation(self):
        results = [child.operation() for child in self.children]
        return f"Composite: [{', '.join(results)}]"

# Client code
if __name__ == '__main__':
    leaf1 = Leaf()
    leaf2 = Leaf()
    composite = Composite()
    composite.add(leaf1)
    composite.add(leaf2)

    print(composite.operation())  # Output: Composite: [Leaf, Leaf]
                

5. Best Practices

• Define a common interface for all components.
• Keep the Composite class simple and focused on managing child components.
• Be cautious with deep hierarchies; they can become complex and difficult to manage.

6. FAQ