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Distributed Architecture Patterns

CQRS & Event Sourcing

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Dylan SmithSenior ALM Consultant

Application Lifecycle Expert

PROFILEDylan is an ALM (Application Lifecycle Management) consultant for Imaginet where he spends his time helping teams become more successful at delivering software. Dylan has over a decade experience designing and architecting mission critical applications. In the past 5 years Dylan has focused on agile development techniques and practices. He has led the shift to agile and lean development practices across multiple teams, projects and companies.

“CQRS+ES differs from most design patterns in that it provides clear business benefits in addition to the obvious technical benefits.”

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Overview• Review Typical

Architecture• What is CQRS?• What is Event

Sourcing?• CODE !!!• Benefits / Concerns

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Data Storage

Domain

Object

Application Services

Remote Facade

Client

Request DTODTO Returned

Send DTOStatus Returned

Repository

Domain Object

Typical Distributed Architecture

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Data Storage

Domain

Object

Command Handlers

Remote Facade

Client

Request DTODTO

Returned

Send CommandAck/Nak

Response

Repository

Domain Object

Query Handlers

Remote Facade

Data Storage

CQRS

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Sample Read Data Model

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Purchase Order

Line Items (n)

Shipping Information

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Order Created

Added 4 Hats

Added 2 Shirts

Shipping Info

Added

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Event Store

Domain

Object

Command Handlers

Remote Facade

Client

Request DTODTO

Returned

Send CommandAck/Nak

Response

Repository

Domain Object

Query Handlers

Remote Facade

Data StorageEvent Bus

CQRS + ES

Event

Handle

rs

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Event Store Data Model

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Command

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Event

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Command Handler

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Domain Object

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Event Handler

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Query Handler

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Data Transfer Object

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vs

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Scalability

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Sample Unit Test

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Sample Unit Test #2

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Client

Domain Read Model

Events

Commands DTOs

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NoSQL Databases

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Other Topics(Time Permitting)• Event Versioning• When to use CQRS/ES?• Using CQRS or ES separately• Concurrency• Eventual Consistency• Asynchronous Commands

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Recommended Reading

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Sample CodeSuper Simple CQRS Example

github.com/gregoryyoung/m-r

NCQRS ncqrs.org

The CQRS Kitchenthecqrskitchen.codeplex.com

Lokad-CQRScode.google.com/p/lokad-cqrs

Fohjingithub.com/MarkNijhof/Fohjin

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Questions?