Code Smell 31 - Accidental Methods on Business Objects

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

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)

view raw accidentalCar.py hosted with ❤ by GitHub

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()

view raw safecar.py hosted with ❤ by GitHub

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