Unique Identity

Value Objects

• Value Objects can serve as holders of unique identity.

• They are immutable which ensures identity stability and centralize any behavior.

• They also provide the benefit of being a Strongly Typed Identifier.

Identity Creation Strategies

User Provides Identity

• A simple approach with complications.

• Can users be relied upon to produce both unique and correct, long-lasting identifies?

• We always have the option of user-provided values as Entity properties available for matching but NOT used for unique identity.

Application Generates Identity

• Highly reliable

• A GUID or UUID is a common approach to identity creation that can produce a completely unique identity.

• We don't normally want to display a UUID in a UI. UUID is appropriate when it can be hidden from users and human-readable reference techniques can be used.

• Parts of a the generated UUID can be used with other attributes to generate a human-readable identifier.

  • TIP: Encapsulate this logic in a custom identity Value Object.

Persistence Mechanism Generates Identity

• Provides unique advantages

• Calling the database for a sequence or incrementing value ensures uniqueness.

• Downside: Performance

  • Takes longer to go to the database to get each value vs. an application-generated Identity.

  • Can potentially be mitigated through caching, but that requires more implementation and potential gaps between identities.

Another Bounded Context Assigns Identity

• An exact match between the local Entity and the remote Entity is the most desirable.

• If the local context uses state from the remote context, we need to synchronize.

  • This is solved using Event Driven Architecture + Domain Events.

  • This leads to more autonomous systems.

  • Important: This is not about caching foreign objects locally. Instead, it involves translating foreign concepts into those of the local Bounded Context.

  • Use this approach conservatively.