|||

Domain Driven Design Core Principles

High Level View

1. Ubiquitous language

  • Same language between product owners and developers.
  • helps efficient communications

2. Bounded Context

  • Define clear boundaries between parts of the system
  • Helps will Microservice architecture

3. Core Domain

  • The actual business problem of the application
  • Not any 3rd party utils / lib code

Entities vs Value Objects

  • Entities have ID and Reference equality
  • Entities are mutable
  • Entities can exist with value objects
  • Entities can be persisted which ValueObjects are a logical grouping of the some data in that entity.
  • Entities cannot be passed between aggregates ~
  • Value objects have reference and structural equality
  • Value objects dont have an ID field and can be treated interchangeably
  • Values objects are immutable
  • Value objects require an entity to be relevant and shouldnt exist outside the entity and do not require separate db tables for persistance, they hold / group logical info together like Money (1c, 2c, 5Dollar etc.)
  • Value objects can be passed between aggregates as they are immutable.

Entity Vs Value Object

Aggregates

  • A conceptual whole
  • Is a logical grouping of Entities
  • An Aggregate has Invariants (a.k.a Validations) that ensures the aggregate is in a consistent state all the time.
  • Every aggregate has a RootEntity. Other aggregates can only talk to the RootEntity and not sub entities.
  • Aggregates should be saved in a single db txn

Entity Vs Value Object

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