ISTA 2016: Event Sourcing

15 – 16 November, SofiaISTACon.org

Event Sourcing

By Vladik Khononov

A New Dimension in Software Design





Agenda• How it happened

• Why it happened

• How event sourcing solves the problem

• Why event sourcing benefits the company


Call Center Management


LEAD• Id• Name• Email• Phone• Status (Available / Follow-up / Closed / Converted)


Name Email Phone Status

Stefan Ivanov [email protected] 03-27243457 Available

Viktor Kovachev [email protected] 08-8332491 Available

Martin Mateev [email protected] 04-8537112 Available

Lilyana Yankov [email protected] 04-6092212 Available

mailto:[email protected]





Name Email Phone Status


Viktor Kovachev [email protected] 08-8332491 Available

Martin Mateev [email protected] 04-8537112 Available

Lilyana Yankov [email protected] 04-6092212 Available







public class Lead {

public long Id { get; set; }

public string Name { get; set; }

public string Email { get; set; }

public string Phone { get; set; }

public LeadStatus Status { get; set; }

public DateTime? FollowupOn { get; set; }

}



SELECT * FROM leads

WHERE [name] LIKE ‘%name%’ OR

[phone] LIKE ‘%phone%’ OR

[email] LIKE ‘%email%’;

WTF???

ISTACon.org


Lead #1410

Name Viktor Radkov

Email [email protected]

Phone 09-9801298

Status Available




PM


…1 month later



PM


…2 months later



PM


Search on stale data

Status change dates

Audit log for BI


PM


PM


public class Lead {







}


Name Email Phone Status Follow-up




Name Email Phone Status Follow-up Date

Stefan Ivanov [email protected] 050-8139904 Follow-up 23/11/2016




Stefan Ivanov [email protected] 050-8139904 Converted








Event Sourcing


Changes=

First class citizens=

Events


Lead Events• Lead Was Initialized (Id)

• Status Changed (NewStatus)

• Name Changed (NewName)

• Contact Information Changed (NewEmail, NewPhone)

• Followup Set (Date)


Lead: Stefan Ivanov• Lead Was Initialized (1410)• Status Changed (Available)• Contact Information Changed ([email protected], 03-27243457)• Status Changed (Followup)• Followup Set (23/11/2016)• Contact Information Changed ([email protected], 050-8139904)• Status Changed (Converted)


public class Lead {public long Id { get; set; }public string Name { get; set; }public string Email { get; set; }public string Phone { get; set; }public LeadStatus Status { get; set; }public DateTime? FollowupOn { get; set; }public void Apply(LeadWasInitialized event) {…}public void Apply(StatusChanged event) {…}public void Apply(NameChanged event) {…}public void Apply(ContactInfoChanged event) {…}public void Apply(FollowupSet event) {…}

}



}

Apply(StatusChanged event) {this.Status = event.NewStatus;

}



}

Apply(NameChanged event) {this.Name = event.NewName;

}



}

Apply(ContactInfoChanged event) {this.Phone = event.NewPhone;this.Email = event.NewEmail;

}



}

Apply(FollowupSet event) {this.FollowUpOn = event.Date;

}


Lead: Stefan IvanovLead Was Initialized (1410)Status Changed (Available)

Contact Information Changed ([email protected],03-27243457)

Status Changed (Converted)

Status Changed (Followup)Followup Set (23/11/2016)

Contact Information Changed ([email protected], 050-8139904)


























public class Lead {







}








public class LeadSearch {public long Id { get; private set; }…public List<string> Emails;public List<string> Phones;…public void Apply(ContactInfoChanged event) {…}…

}

Apply(ContactInfoChanged event) {this.Phones.Append(event.NewPhone);this.Emails.Append(event.NewEmail);

}


public class LeadStatusChangesModel {public long Id { get; set; }public List<StatusLog> StatusChangesLog;…public void Apply(StatusChanged event) {…}…

}Apply(StatusChanged event) {this.StatusChangesLog.Append(

new StatusLog(event.NewStatus, DateTime.Now);

);


public class LeadStatusChangesModel {public long Id { get; set; }public List<StatusLog> StatusChangesLog;…

}

public class Lead {public long Id { get; set; }public string Name { get; set; }public string Email { get; set; }public string Phone { get; set; }public LeadStatus Status { get; set; }public DateTime? FollowupOn { get; set; }…

}

public class LeadSearch {public long Id { get; private set; }public List<string> Emails;public List<string> Phones;…

}








Events = Source of Truth

Event Sourcing





Storage: Event Store


Event Store API: The Good News

Append(Entity Id + New events)

GetEvents(Entity Id)Event1,Event2,Event3,

….


Key (Entity Id) Value (Events list)

Lead #1410 1. LeadWasInitialized(1410)

2. StatusChanged(Available)

3. NameChanged(“Martin Mateev”)

4. StatusChanged(Converted)


2. StatusChanged(Available’’’)

3. NameChanged(“Lilyana Yankov”)


Event Store API: The Good News



….


Event Store API: The Bad News



….


CQRSCommand Query Responsibility Segregation


CQRS• Command - write data• Query - read data• A use case can be either Command or Query. Never both


Queries

Read Model

Read DB

Commands

Write Model

Writes DBProjection engine


Event Sourced Model (Write)




4. StatusChanged(Closed)

…

1000. StatusChanged(FollowUp)

1001. FollowupSet(16/11/2017)

Read Model

Id 1410

Name Martin Mateev

Status Followup

FollowupOn (Empty)

Email …

Phone …


Queries

Read Model

Read DB

Commands

Write Model

Writes DBProjection engine


Event Sourced Model (Write)




4. StatusChanged(Closed)


6. NameChanged(“Viktor Rumenov”)

Read Model

Id 1410

Phone …

Status Available

FollowupOn (Empty)

Email …

Name Martin Mateev



}

Apply(NameChanged event) {this.Name = event.NewName;

}


Queries

Read Model

Read DB

Commands

Event Sourcing

Event StoreProjection engine


Queries

Read Model

Read DB

Commands

Write Model

Writes DBProjection

engine

Projection• RDBMS• Documents• Graphs• Files


Queries

Read Model

Commands

Write Model

Writes DBProjection

engine

Projection• RDBMS• Documents• Graphs• Files• Multiple DBs

Read DBs


Queries

Read Model

Commands

Write Model

Writes DBProjection

engine

Read DBs

Concurrency• Pessimistic• Optimistic• Optimistic on steroids


SetFollowupCommand + StatusChangeEvent => Collision

ChangeNameCommand + StatusChangeEvent => OK


Event Sourcing + CQRS• Flexible business domain modeling• Insane scalability and availability• Rock solid infrastructure

• …look great on your C.V.



CQRS: When?

Event Sourcing ➡ CQRS

Non-functional benefits


Event Sourcing

CQRS


Event Sourcing: When?

?


SubdomainsGeneric, Supporting, Core



SubdomainsGeneric, Supporting, Core


CREATIVE CATALOG

CAMPAIGN PUBLISHING

BILLING USERS MANAGEMENT

LEAD MANAGEMENTCOMMISSIONS CALCULATION

DESK MANAGEMENTVOIP MANAGEMENT

EMAIL CAMPAIGNS


Generic Subdomains


CREATIVE CATALOG

CAMPAIGN PUBLISHING




EMAIL CAMPAIGN


CREATIVE CATALOG

CAMPAIGN PUBLISHING




EMAIL CAMPAIGN


Supporting Subdomains


CREATIVE CATALOG

CAMPAIGN PUBLISHING




EMAIL CAMPAIGN


CREATIVE CATALOG

CAMPAIGN PUBLISHING




EMAIL CAMPAIGN


Core Domains


CREATIVE CATALOG

CAMPAIGN PUBLISHING




EMAIL CAMPAIGN


Event Sourcing: When?

Core business domains


Before you try this at home


Available Event Stores

• http://GetEventStore.com

• NEventStore

• Akka Persistence

• Elastic Event Store (Coming soon)

http://GetEventStore.com



€100 Discount for attendees of ISTA 2016https://ti.to/webengineers/ddd17/discount/istacon2016

https://ti.to/webengineers/ddd17/discount/istacon2016


Domain-Driven Design

• How to identify subdomains?

• How to define business entities?

• How do define events?

• How to talk to business experts?



Thank you!

@vladikk

vladikk.com

vladikkhononov

[email protected]

ISTA 2016: Event Sourcing

Engineering