readme.md

Code Smell 31 - Accidental Methods on Business Objects

Adding persistence, serialization, displaying, importing, exporting code to an object bloats its protocol and brings coupling.

TL;DR: Don't pollute your business obejcts with accidental behavior

Problems

• Readability

• Coupling

• Maintainability

Solutions

1. Keep your objects clean.

2. Decouple business objects.

3. Separate accidental concerns: Move Persistence, Formatting, Serialization to special objects.

4. Keep essential protocol using bijection.

Examples

• Persistence

• Identifiers

• Serialization

• Formatting

Sample Code

Wrong

class car:

    def __init__(self, company, color, engine):
        self._company = company
        self._color = color 
        self._engine = engine
    
    def goTo(self, coordinate):        
        self.move()
        
    def startEngine(self):
        ## code to start engine
        self.engine.start()
    
    def display(self):
        print ('This is a', self._color, self.company)
        ## Displaying is accidental
        
    def toJSon(self):
        ## Serializing is accidental
        return "json"
        
    def updateOnDatabase(self):
        ## Persistence is accidental
        this.database.update(this)
        
    def getId(self):
        ## identifiers are accidental
        return id;
        
    def fromRow(self, row):
        ## Persistence is accidental
        this.database.convertFromRow(row, this);
        
    def forkCar(self):
        ## Concurrency is accidental
        ConcurrencySemaphoreSingleton.getInstance().forkCar(this)

Right

class car:

    def __init__(self,company,color,engine):
        self._company = company
        self._color = color 
        self._engine = engine
    
    def goTo(self, coordinate):        
        self.move()
        
    def startEngine(self):
        ## code to start engine
        self.engine.start()

Detection

It is difficult (but not impossible) to create linting rules based on naming and hinting for suspect names.

Exceptions

• Some frameworks force us to inject dirty code in our objects. (For example identifiers).

We should try to use better languages/frameworks.

Tags

• Declarative

Conclusion

We are very used to see business objects polluted. This is normal. We need to reflect on the consequences and coupling from these designs.

Credits

Photo by Robert Bye on Unsplash

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Simple things should be simple, complex things should be possible.

Alan Kay

Software Engineering Great Quotes

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This article is part of the CodeSmell Series.

How to Find the Stinky Parts of your Code