Code Smell 01 - Anemic Models

Code Smell 01 - Anemic Models

Your objects have no behavior.

Maxi Contieri
·Oct 20, 2020·

2 min read

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Table of contents

  • Problems
  • Solutions
  • Examples
  • Sample Code
  • Detection
  • Also Known as
  • Tags
  • Conclusion
  • Relations
  • More info
  • Credits

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

Protocol is empty (with setters/getters).

If we ask a domain expert to describe an entity he/she 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

Tags

  • Anemic
  • OOP as Data
  • Encapsulation
  • Setters/Getters
  • Mutability

Conclusion

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

Relations

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.

 
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Technical Opinions are my own. I don't have the revealed truth.

Software Design is a creative activity. These are hints and not rigid rules.

I write on BackEnd Business Systems and OOP Design. My advice/experience might not suit other systems.

You can write me at info(at)maximilianocontieri.com