Presentation slides from sessions discussing Event Source data storage and read-model projections. Source code from demos at: https://bitbucket.org/csharpfritz/nerddinner-cqrs

1. Jeffrey T. Fritz
@csharpfritz
http://csharpfritz.com

2. Jeffrey T. Fritz
ASP.Net Developer Evangelist for Telerik
AJAX controls
Microsoft MVP, ASPInsider
Tech Ed 2012 Speaker Idol Finalist, 2013
Runner-up
15 years of web development experience
CodeProject.tv + Pluralsight author
(coming soon!)
May 2013 MSDN Magazine: One ASP.Net
DotNetRocks #855
Yet Another Podcast #98, #106

3. Level setting: n-tier architecture
Event Sourcing – definition, benefits,
challenges
How do I get started?
How do I audit?
Rebuilding and Reporting Samples

4. Presentation Layer
Business Logic Layer
Data Access Layer
Database

5. Event Sourcing: An architectural pattern
which warrants that your entities do not track
their internal state by means of direct
serialization or O/R mapping, but by means
of reading and committing events to an event
store
Event: an immutable object that describes a
change that has occurred to an entity.

6. Entities are not stored as a given state in time
Changes to the entities are persisted
Stored in the order changes were applied to
the object
No concern for ‘prior state’ of the entity

7. Image courtesy of Greg Young

11. Simplified data access
◦ Append-only data store
◦ Easy to partition
◦ Easy to replicate
Event structure allows for greater use of
‘ubiquitous language’
Reporting requirements are required to be
stored separately

12. Performance
◦ Documented performance on an i7 laptop with SSD
storage:
15,000 writes / second
50,000 reads / second
◦ Aggressively cache query results
Data never changes

13. Testing
◦ Given (Collection of Events)
◦ When (Action)
◦ Then (Events expected)
No duplicate storage of data
◦ Current State
◦ Audit log

14. Tivo for your entities
◦ Trivial to ‘replay’ the events to a given point in time
Offline processing
Conflict Management

15. Not storing data in relational structure
◦ Can use RDBMS as a store
Reporting is NOT immediately available
Difficult to migrate a legacy app to
Harder to sell to an organization

16. ObjectID Change
Date
Change
User
Field Old Value New Value
1 9/20/12 Jeff Attend 0 1
ObjectID Version DateStamp Event
1 5 9/20/12 RsvpChanged {
Name: Jeff,
Attending: true
}

17. Jonathan Oliver EventStore
◦ .Net based tool
◦ Supports storage in: MySQL, MSSql, SQLite, Access,
Sql Azure, Amazon RDS, Oracle, Sybase, Postgres,
DB2, RavenDb, MongoDb, CouchDb, and LOTS more
◦ http://github.com/joliver/EventStore
Greg Young Event Store
◦ JSON based event store
◦ Proprietary storage engine
◦ RESTful access
◦ http://geteventstore.com

18. Demo:
Jonathan Oliver Event Store
Get and Save

19. AuditLog is just a dump of events
Call ToString on each event
Demo – NerdDinner AuditLog

20. Data can be “re-projected” into any format
New data can be discovered by the projection
that wouldn’t normally be visible in 3rd
normal form
Alternate storage of data in format for the
report desired

21. Offline re-build of reporting data
NerdDinner.Rebuild

22. Use AAA syntax
◦ Arrange (collection of events)
◦ Act (action)
◦ Assert (verify output of events)

23. http://bit.ly/FritzES -- Event Sourcing Links
http://csharpfritz.com
@csharpfritz on Twitter
Thanks for attending!