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Code Smell 40 - DTOs

Maxi Contieri
Learn something new every day. - I am a senior software engineer working in industry, teaching and writing on software design, SOLID principles, DDD and TDD.
・2 min read

DTOs are widely used and they 'solve' real problems, do they?

Problems

  • Anemic Object

  • Inconsistent Data

  • Duplicated logic

  • Duplicated structure

  • Class Polluting

  • Information Hiding Violation

  • Code repeated among mutators, accessors, serializers, parsers

  • Ripple Effect

  • Data integrity

Solutions

  1. Transfer anemic data on arrays.

  2. Use real business objects.

  3. If we want to transfer partial objects: use proxies or null objects to break the reference graph.

Sample Code

Wrong

Right

Detection

We can use the same anemic object detectors.

We can check for anemic classes with no business object behavior (removing serializes, constructors, mutators etc).

# Tags

  • Anemic

Conclusion

DTOs are a tool and an established practice in some languages. We should use them with care and responsibility.

If we need to disassemble our objects in order to send them away from our realms, we need to be extremely cautioned. Since dismembered objects have no integrity considerations.

His author warns us about its actual abuse.

Relations

More info

Martin Fowler's

Refactoring.Guru

Stack Exchange


The best smells are something that's easy to spot and most of time lead you to really interesting problems. Data classes (classes with all data and no behavior) are good examples of this. You look at them and ask yourself what behavior should be in this class.

Martin Fowler

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