CQRS innovations (English version)

April 12, 2023 www.ExigenServices.com

CQRS - Innovative solution for problems of modern enterprise architectures.

Andrey Lomakin ([email protected]) Artem Orobets ([email protected])

2 www.ExigenServices.com

Table of content

1. Why CQRS ?

a) Milestones of enterprise architecture history

b) Pitfalls of CRUD

c) CQRS as solution

2. CQRS internals

3. Axon framework as CQRS implementation


Why CQRS ?

I. Why CQRS ?


Lets talk about evolution of enterprise architecture

?

Back to the beginning


Evolution of presentation of documents

Epoch of paper documents


Evolution of presentation of documents

Epoch of electronic storages



Search in electronic storage



Epoch of CRUD architecture has came


Evolution of data processing

Epoch of business processes


CRUD approach is oriented on data manipulation, but not on business

logic modeling .

However…


Pitfalls of CRUD

II. Pitfalls of CRUD


Problem #1. Usage of JavaBeans ….

JavaBean – “Reusable software components that can be manipulated visually in a builder tool”.


1. Broken encapsulation of business objects.

2. Worse code readability.3. Harder maintainability.4. All business logic

is placed in service methods.

… results in …


Problem #2. Performance optimization and consequences.

Usage of ORM tools with denormalization dilutes


Problem #3. Scalability

During business data processing we always chose C in CAP theorem


Problem #4:In real life concurrent data modification conflicts do not exist.

Real life business processes do not have concurrent data modification conflicts.

Detection of such conflict is sign of flaw in implementation of business logic.

CRUD does not take this into account.


CQRS as solution

III. CQRS as solution


CQRS

CQRS - Command Query Responsibility Segregation


Problem # 1: Usage of JavaBeans

JavaBeans are still used on query side onlybut JavaBean != Domain Entity.


Problem #2. Performance optimization and consequences.

Data denormailzation is used on query side only


Data on query side

Each table – reflection of presentation of data on user screen.

Database are not restricted to be SQL only.

Possible alternatives - Apache Cassandra, HBase, OrientDB ….


Problem #3. Scalability

Data consistency is needed on business logic side only.

On query side eventual consistency is totally acceptable.


Problem #4:In real life concurrent data modification conflicts do not exist.

1. In the form of values of variables inside object

Two approaches to present object state



+11.2 M $ + 5.3 M $ - 8.2 M $

Sum: 8.3 M $

2. In form of event queue



Each aggregate (DDD) – event container. There is no need to use relational

databases. It is preferable to have DB with ACID

properties.



Advantages: System monitoring support. Ability rollback system state till any moment

in the past. Framework for data replication and conflict

resolution.


Conflict resolution

Correct customer address

Customer reallocated

Conflict resolver

Customer reallocated


Architecture of CQRS applications

IV. Architecture of CQRS applications


CQRS – is approach only

CQRS is approach only, how it will be implemented, depends

on you.


Queries

Multilayer architecture

DB query

CQRS

Conversion to domain model

Conversion to DTO

Transmutation of datato client

DB query

Conversion to domain model

Conversion to DTO

Transmutation of datato client


Commands

Command – presentation of business action, action which is meaningful for end user.

Advantages of usage of commands:1. Orientation on business problems.2. Convenient facilities for monitoring and scalability.


….advantages…..

1. Good preconditions for DDD usage.2. Usage of complex event processing

possibilities.3. Simplicity of distribution of responsibilities

between highly specialized commands.


CQRS frameworks

V. CQRS frameworks


Axon framework

Axon framework - most popular and feature rich.


Example of CQRS application

Address Book – address list management


Command creation and submission


Command processing


Business action


Event processing on query side


Query side


Simplicity of configuration


Axon – repository и event store.

Repository

Event Store

JPA

File System JPA Mongo DB


Event Stores – pros and cons

There is no ACID support better performance

JPA Event Store

Transactional but slow

Mongo DB, File system


Questions


Authors

Artem Orobets. twitter: @Dr_EniSh , [email protected], skype: dr_enish

Andrey Lomakin. twitter: @Andrey_Lomakin , [email protected] , skype: lomakin_andrey

mailto:[email protected]

mailto:[email protected]


Sources

1. First CQRS introduction http://www.infoq.com/presentations/greg-young-unshackle-qcon08

2. CQRS architecture overview - http://elegantcode.com/2009/11/11/cqrs-la-greg-young/

3. Greg Young blog - http://codebetter.com/gregyoung/

4. Race conditions does not exist http://www.udidahan.com/2010/08/31/race-conditions-dont-exist/

5. Domain Driven Design Aggregator - http://domaindrivendesign.org/

6. Axon framework home page - http://code.google.com/p/axonframework/

7. Mark Nijhof blog http://cre8ivethought.com/blog

http://www.infoq.com/presentations/greg-young-unshackle-qcon08

http://www.infoq.com/presentations/greg-young-unshackle-qcon08

http://elegantcode.com/2009/11/11/cqrs-la-greg-young/



http://codebetter.com/gregyoung/

http://codebetter.com/gregyoung/

http://www.udidahan.com/2010/08/31/race-conditions-dont-exist/

http://www.udidahan.com/2010/08/31/race-conditions-dont-exist/

http://domaindrivendesign.org/



http://code.google.com/p/axonframework/

http://code.google.com/p/axonframework/

CQRS innovations (English version)

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