Code Smell 50 - Object Keys

Code Smell 50 - Object Keys

Primary keys, IDs, references. The first attribute we add to our objects. They don't exist in the real world.

TL;DR: Reference objects with objects, not ids.



  1. Reference object to objects.

  2. Build a MAPPER.

  3. Only use keys if you need to provide an external (accidental) reference. Databases, APIs, Serializations.

  4. Use dark keys or GUIDs when possible.

  5. If you are afraid of getting a big relation graph use proxies or lazy loading.

  6. Don't use DTOs.

Sample Code




This is a design policy.

We can enforce business objects to warn us if we define an attribute or function including the sequence id.


  • Accidental


Ids are not necessary for OOP. You reference objects (essential) and never ids (accidental).

In case you need to provide a reference out of your system's scope (APIs, interfaces, Serializations) use dark and meaningless IDs (GUIDs).


More info


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All problems in computer science can be solved by another level of indirection.

David Wheeler

This article is part of the CodeSmell Series.