Code Smell 01 - Anemic Models

Your objects have no behavior

8 July, 2022

Contributors

Maxi Contieri

@mcsee

TL;DR: Don't use objects as data structures

The protocol is empty (with setters/getters).

If we ask a domain expert to describe an entity they would hardly tell it is 'a bunch of attributes'.

Problems

No Encapsulation.
No mapping to real-world entities.
Duplicate Code
Coupling
Writer / Reader mismatch.

Solutions

1) Find Responsibilities.

2) Protect your attributes.

3) Hide implementations.

4) Delegate

Examples

DTOs

Sample Code

Wrong

class Window:
    def __init__(self):
        self.height = None
        self.width = None

    def getHeight(self):
        return self.height

    def setHeight(self, height):
        self.height = height

    def getWidth(self):
        return self.width

    def setWidth(self, width):
        self.width = width

Right

class GraphicWindow:

  def area(self):
    # implementation
    return

  def open(self):
    # implementation
    return

  def isOpen(self):
    # implementation
    return

Detection

Sophisticated linters can automate detection. They should ignore setters and getters and count real behavior methods.

Also Known as

Data Class

Conclusion

Avoid anemic models. Focus always on protocol instead of data. Behaviour is essential, data is accidental.

Relations

https://maximilianocontieri.com/code-smell-28-setters

https://maximilianocontieri.com/code-smell-15-missed-preconditions-1

More info

Object-oriented programming increases the value of these metrics by managing this complexity. The most effective tool available for dealing with complexity is abstraction. Many types of abstraction can be used, but encapsulation is the main form of abstraction by which complexity is managed in object-oriented programming.

Rebecca Wirfs-Brock

Credits

Photo by Stacey Vandergriff on Unsplash

This article is part of the CodeSmell Series.