How-To Guides on Advanced Beginner

Defining Aggregate Boundaries

d8lzz1gpw@mozmail.com (kimbenji) — Sat, 10 Jan 2026 00:00:00 +0000

Problem It Solves: Performance issues from making Aggregates too large, or consistency violations from making them too small Time Required: ~30 minutes Prerequisites: Assumes you have read the Aggregate Deep Dive document

Success Criteria
After completing this guide, you will be able to:

Identify invariants to determine Aggregate boundaries

Decide whether to include an Entity using 4 key questions

Recognize signals when boundaries are wrong

1. Identify Core Invariants#

An Invariant is a business rule that must always be true. It is the most important criterion for defining Aggregate boundaries.

Identifying Bounded Contexts

d8lzz1gpw@mozmail.com (kimbenji) — Fri, 16 Jan 2026 00:00:00 +0000

Problem Solved: Unsure how to divide the system, or high inter-team dependencies due to incorrectly defined Context boundaries Time Required: ~25 min Prerequisites: Assumes you have read the Strategic Design document

Success Criteria
After completing this guide, you will be able to:

Identify Context boundaries using 3 signals

Validate boundaries through domain expert interviews

Recognize and fix symptoms of incorrect boundaries

1. Detecting Signals That Indicate Context Boundaries#

Check the following 3 signals to determine if Bounded Context separation is needed.

Designing Value Objects

d8lzz1gpw@mozmail.com (kimbenji) — Fri, 16 Jan 2026 00:00:00 +0000

Problem Solved: High complexity from making everything an Entity, or low type safety due to Primitive Obsession Time Required: ~20 min Prerequisites: Assumes you have read the Tactical Design document

Success Criteria
After completing this guide, you will be able to:

Distinguish Entity from Value Object using 3 questions

Implement Value Objects using Java Records

Refactor Primitive Obsession to Value Objects

1. Distinguishing Entity vs Value Object#

1.1 Three Decision Questions#

Apply the following questions in order:

Designing Domain Events

d8lzz1gpw@mozmail.com (kimbenji) — Fri, 16 Jan 2026 00:00:00 +0000

Problem Solved: Complex transactions due to tight coupling between Aggregates, or difficulty propagating changes Time Required: ~25 min Prerequisites: Assumes you have read the Aggregate Deep Dive document

Success Criteria
After completing this guide, you will be able to:

Identify situations that need domain events

Apply event naming conventions and payload design

Implement Spring event publishing/subscribing patterns

1. Identifying Situations That Need Domain Events#

1.1 Three Signals That Indicate Events Are Needed#

Check the following 3 signals to determine if domain events are needed.