(src: https://www.youtube.com/watch?v=9ZgSz6xAfL8)

Model: Clue Bucket (aka toolbox)

Model: Patterns vs Principles vs Heuristics

Model: distill your heuristics

Model: competing heuristics

Heuristic: things that change together should stay together

• named: Single Responsibility

Model: Method for deliberate design choices

Exercise

Model: Domain Event

Exercise: Which attributes should be in this domain event?

• who placed it

• when was it placed

• • Heuristic: when did something happen, is that relevant?

  • Heuristic: what are all the timestamps that matter

  • • when it happened

    • when we learned about it

    • when we recorded it

    • pre-dated

• who cares about this? what do they need

• what was ordered

heuristics for deciding what to put in there

• always verify assumptions about time

• • consumer sees it immediately or later

  • data could change over time

  • what if a constraint / business rule / invariant is not met immediately but some time goes by

• redundancy

• • minimal events

  • Model: Fat events

  • Heuristic: consumer might not listen to all events

  • Heuristic: immutable attributes we should probably add in there

  • • mutable: name

    • immutable: customer_id

• consumer

• • Heuristic: serve the consumers needs

  • Heuristic: ignore individual consumer's needs

  • Heuristic: 80-20 the consumers needs

  • DDD context mapping patterns

• • • Pattern: internal to  our bounded context, easily changeable

    • Pattern: conformist: leak into my domain

    • Pattern: partnership: their success relies on our success

• • • Pattern: open host service (eg. Google Maps)

• • how many consumers are there

  • • 1

    • 5-10 consumers -> 80-20 rule?

• Temporal Coupling

• • are the consumers gonna query us to get more data

  • Model: Notification vs Domain Event

  • temporal coupling:

  • • "This system needs to be online at the time that the consumer wants to know what the order was like"

    • reduces our autonomy

    • if not online, I can't do anything

• Heuristic: sensitive information

• • Datasparsamheid

  • GDPR compliance

  • sensitive information

• Heuristic: how would it look in a paper world?

• Heuristic: can we do multiple events for the same event, specific per consumer

Heuristic: if you can imagine it as a 3rd party system, then you can have it as a bounded context

Notifications - forces a lookup

Domain Events - completeness guarantee

Fat events - redundant information

• safe, immutable, stable

• evolve over time, mutable

• sensitive information, supposed to throw away after a certain amount of time