2. EXORCISM
“THE PRACTICE OF EVICTING DEMONS OR OTHER SPIRITUAL ENTITIES
FROM A PERSON OR AN AREA THEY ARE BELIEVED TO HAVE POSSESSED”

3. CQRS
DISTRIBUTED DOMAIN DRIVEN DESIGN

4. Classic Architecture
Client executes interactors
Interactor modifies data and returns ViewModel

5. Step 1: CQS
Command/Query segregation
Commands - write data, void
Queries - read data

6. Step 1: CQS
public class SubmitAction : Interactor
{
public ShowLeadViewModel Execute(LeadActionDTO action)
{
var lead = ExecuteLeadAction(action);
var viewModel = BuildViewModel(lead);
return viewModel;
}
}

7. Step 1: CQS
public class SubmitAction : Interactor
{
public void Execute(LeadActionDTO action)
{
ExecuteLeadAction(action);
}
public ShowLeadViewModel GetLeadInfo(long id)
{
var lead = GetLead(id);
var viewModel = BuildViewModel(lead);
return viewModel;
}
}

8. Step 1: CQS
public class SubmitAction : Interactor
{
public void Execute(LeadActionDTO action)
{
ExecuteLeadAction(action);
}
public ShowLeadViewModel GetLeadInfo(long id)
{
return GetLeadViewModel(id);
}
}

9. Step 1: CQS
Separated Query/Command logic
Commands are executed asynchronously
Queries are executed though a thin read layer

10. Normalization: 3NF vs.
1NF
lead_id
status_id
queue_id
contact_id
campaign_
id
assigned_t
o_id
1043
1
2
241734
54
108
1044
3
5
241771
78
109
lead_id
status
queue
contact_n
ame
campaign
assigned_t
o
1043
New
Wait
Yau Siong
1043
Contacted
Converted
Dimas
Wijaya
Saraya
[03SEP2012]
Gunggo_C
A [060512]
Alex
Delors
Mona
Barbara

11. Step 2
Write model: 3NF
Read model: 1NF

12. Step 2

13. Step 2: Events

14. Step 2: Events
Multiple projections
Scalable reads
Decoupled storage mechanism
RDMBS, Document store, Key/Value store, plain
files (local or S3), Sharepoint List, Lucene, Cloud
Search
No need for NHibernate Profiler licenses

15. Step 2: Events

16. No reliable source of truth.

17. Step 3

18. Step 3: Events History

19. Step 3: Events History
Every data change is logged
Reliable source of truth
Read model can be regenerated anytime
Write model can be regenerated anytime

20. Step 3: Events History

21. Writes are not scalable.

22. Step 4

23. Step 4
var lead1 = {
“leadId”: 15423,
“customer_id”: “zubby@bubby.com”,
“events”: [
{ “type”: “lead_created”, “data”: {…}, “date”: “20131216T1242” },
{ “type”: “lead_assigned”, “data”: {…}, “date”: “20131216T1342” },
{ “type”: “activity_created”, “data”: {…}, “date”: “20131216T1432” },
{ “type”: “new_lead_event”, “data”: {…}, “date”: “20131216T1522” },
{ “type”: “activity_created”, “data”: {…}, “date”: “20131216T1432” }
]
}

24. Step 4

25. Step 4: Event Sourcing

26. Step 4: Event Sourcing
Infinitely scalable reads
Infinitely scalable writes
Audit data
New business insights form past data
Replay events for debugging and analysis
Retroactive logic changes (=bug fixes)
Lightweight backups
NoSQL
No deadlocks
No DBA
CHEAP!!!!!

27. CQRS
Commands
Events
Event Store
ViewModels / Projections

28. Questions?

29. DDD: Building Blocks
Domain Driven Design
Entity
Aggregate
Repository

30. DDD: Aggregate
shoppingCart = {
“id”: 1234,
“items”: [{
{ “product_id”: 123, “amount”: 1, “price”: 10},
{ “product_id”: 123, “amount”: 1, “price”: 10}
}]
}