CQRS and Event Sourcing, An Alternative Architecture for DDD
![CQRS & Event Sourcing,[object Object],An alternative architecture for DDD,[object Object],Dennis Doomen,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-1-2048.jpg?cb=1666084456)
![The default architecture,[object Object],A better architecture,[object Object],The alternative architecture,[object Object],Advanced topics ,[object Object],Contents,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-2-2048.jpg?cb=1666084456)
![The Default Architecture,[object Object],Easy to build,[object Object],Accepted by management,[object Object],Well known,[object Object],Lots of resources,[object Object],Lots of frameworks,[object Object],Silverlight Application,[object Object],No concurrency,[object Object],Scalability limited,[object Object],No domain verbs,[object Object],Granularity DTOs,[object Object],Unneccesary DTO conversions,[object Object],Conflicting demands,[object Object],Proxy,[object Object],DTOs,[object Object],Services,[object Object],Domain Services,[object Object],Domain Model,[object Object],Repositories,[object Object],Unit of Work,[object Object],Service Agents,[object Object],RelationalDatabase,[object Object],Backoffice Systems,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-3-2048.jpg?cb=1666084456)
![CQRS,[object Object],Silverlight Application,[object Object],Commands are verbs,[object Object],No DTO conversion,[object Object],Easy to build disconnected clients,[object Object],Query Store = No SQL,[object Object],Very scalable,[object Object],Service Agent,[object Object],Queries,[object Object],Business Actions,[object Object],DTOs,[object Object],Commands,[object Object],Command Service,[object Object],Query Service,[object Object],Command Handlers,[object Object],Domain Services,[object Object],Domain Model,[object Object],Data Access Layer,[object Object],Repositories,[object Object],UoW,[object Object],Service Agents,[object Object],Difficult to sync database,[object Object],No concurrency,[object Object],Requires a task-based UI,[object Object],Complexity,[object Object],RelationalDatabase,[object Object],Query Store,[object Object],Backoffice Systems,[object Object],Changes,[object Object],Query Store,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-4-2048.jpg?cb=1666084456)
![Task-based UIs a.k.a. Inductive UIs answer:,[object Object],What am I supposed to do now?,[object Object],Where do I go from here to accomplish my task?,[object Object],Task-based UIs,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-5-2048.jpg?cb=1666084456)
![Focus screens on single task,[object Object],Make the task’s intention clear,[object Object],Offer links to secondary tasks,[object Object],Provide screens for starting tasks,[object Object],Make the next step obvious,[object Object],From Microsoft Inductive User Interface Guidelines,[object Object],Guidelines for Task-based UIs,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-6-2048.jpg?cb=1666084456)
![Are valid or not, regardless of context,[object Object],Named in Ubiquitous Language,[object Object],State intent,[object Object],Can be asynchronous...,[object Object],...but beware of eventual consistency,[object Object],Rejection via exception or fault event,[object Object],Commands,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-7-2048.jpg?cb=1666084456)
![One table per UI view,[object Object],Exposed through ,[object Object],SOA-style web services,[object Object],WCF data services,[object Object],WCF RIA Services,[object Object],Can be anything,[object Object],Relational Database,[object Object],No SQL database,[object Object],XML files,[object Object],Query Store,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-8-2048.jpg?cb=1666084456)
![CQRS & Event Sourcing,[object Object],Silverlight Application,[object Object],Great performance,[object Object],Conflict Merging,[object Object],Historical Tracking,[object Object],Trival Synchronization,[object Object],Easy Integration,[object Object],Independent Query Store ,[object Object],Queries,[object Object],Service Agent,[object Object],Business Actions,[object Object],Commands,[object Object],DTOs,[object Object],Command Service,[object Object],Command Handlers,[object Object],Domain Services,[object Object],Domain Model,[object Object],Events,[object Object],Query Service,[object Object],Denormalizer,[object Object],Events,[object Object],Event Handlers,[object Object],Lots of new concepts,[object Object],Not so acceptable,[object Object],Few resources,[object Object],No consensus yet,[object Object],More complexity,[object Object],Aggregate boundaries important,[object Object],Data Access Layer,[object Object],UoW,[object Object],Event Bus,[object Object],Domain Repository,[object Object],Service Agents,[object Object],Query Store,[object Object],Event Store,[object Object],Query Store,[object Object],Backoffice Systems,[object Object],Events,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-9-2048.jpg?cb=1666084456)
![Represent state changes in aggregate root,[object Object],Named in passed tense,[object Object],Using Ubiquitous Language,[object Object],Entire aggregate is stored in serialized format,[object Object],Events never change,[object Object],Snapshots to improve performance,[object Object],Events,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-10-2048.jpg?cb=1666084456)
![Have no relationships (!),[object Object],Communicate through events,[object Object],Entities do not expose setters (!),[object Object],Apply events to themselves,[object Object],State exposed as mementos,[object Object],Aggregate Roots,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-11-2048.jpg?cb=1666084456)
![Conflict Merging,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-12-2048.jpg?cb=1666084456)
![Event Schema Versioning,[object Object],- Adds missing properties,[object Object],- Renames renamed properties,[object Object],- Converts values,[object Object],Post Converter,[object Object],Property Bag Converter,[object Object],Post Converter,[object Object],Post Converter,[object Object],id = 123,[object Object],SQL Server,[object Object],Domain Repository,[object Object],Event Store,[object Object],Property,[object Object],Bag,[object Object],Get(id = 123),[object Object],Event,[object Object],id = 123,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-13-2048.jpg?cb=1666084456)
![Event Store != relational database...so no unique constraints,[object Object],Workarounds,[object Object],Check uniqueness through query side,[object Object],Add generic unique column to event store,[object Object],Introduce a parent that enforces uniqueness,[object Object],Unique Constraints,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-14-2048.jpg?cb=1666084456)
![The CQRS Kitchen,[object Object],Views (XAML + C#),[object Object],View Models,[object Object],Application Services,[object Object],Unity,[object Object],Service Agent,[object Object],Commands,[object Object],DTOs,[object Object],Command Service,[object Object],Command Handlers,[object Object],WCF,[object Object],Domain Services,[object Object],Mementos,[object Object],Domain Model,[object Object],Unity,[object Object],Enterprise Library 5,[object Object],NCQRS++,[object Object],NSerivceBus,[object Object],Events,[object Object],Event Handlers,[object Object],Event Bus,[object Object],Domain Repository,[object Object],Events,[object Object],UoW,[object Object],Event Store,[object Object],Query Service,[object Object],Denormalizers,[object Object],WCF Data Services,[object Object],Thin Data Access Layer,[object Object],Entity Framework 4,[object Object],SQL Server,[object Object],Entity Framework 4,[object Object],SQL Server,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-15-2048.jpg?cb=1666084456)
![NCQRS,[object Object],The CQRS framework for .NET http://ncqrs.codeplex.com/,[object Object],Very promising,[object Object],Great Documentation,[object Object],Quality code,[object Object],Uses Code Contracts,[object Object],Very active team,[object Object],I’m considering joining ,[object Object],(Still) difficult to get started,[object Object],Not proven yet,[object Object],Not complete yet,[object Object],Feels a bit too complex,[object Object],Not everything is pluggable,[object Object],Misses a coding standard,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-16-2048.jpg?cb=1666084456)
![In summary,[object Object],Great for performance,[object Object],Very scalable,[object Object],Supports historical auditing,[object Object],Supports high concurrency,[object Object],Easy to integrate with other systems,[object Object],Very testable with TDD/DDD,[object Object],Aligns great with Ubiquitous Language,[object Object],Doesn’t require expensive RDBMS,[object Object],Lots of new concepts,[object Object],Lots of choices to make,[object Object],Not yet accepted by management,[object Object],Limited documentation,[object Object],No consensus yet,[object Object],More complexity,[object Object],Aggregate design is important,[object Object],I haven’t found all issues yet,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-17-2048.jpg?cb=1666084456)
![Background InformationGreg Young, Mark Nijhof, Udi Dahan, Jonathan Oliver,[object Object],Example Code, FrameworksThe CQRS Kitchen, NCQRS,[object Object],Interaction Design / Task-Based UIsThe Inmates Are Running The Asylum, Alan CooperMicrosoft Inductive User Interface Guidelines,[object Object],Links,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-18-2048.jpg?cb=1666084456)
![Emaildennis.doomen@avivasolutions.nl,[object Object],Twitter,[object Object],ddoomen,[object Object],Blogwww.dennisdoomen.net,[object Object],Questions?,[object Object]](https://image.slidesharecdn.com/cqrseventsourcingdotned2010-05-100528004537-phpapp01/75/cqrs-and-event-sourcing-an-alternative-architecture-for-ddd-19-2048.jpg?cb=1666084456)
CQRS and Event Sourcing, An Alternative Architecture for DDD
Most of us will be familiar with the standard 3- or 4-layer architecture you often see in larger enterprise systems. Some are already practicing Domain Driven Design and work together with the business to clarify the domain concepts. Perhaps you’ve noticed that is difficult to get the intention of the 'verbs' from that domain into this standard architecture. If performance is an important requirement as well, then you might have discovered that an Object-Relational Mapper and a relational database are not always the best solution. One of the main reasons for this is the fact that the interests of a consistent domain that takes into account the many business rules, and those of data reporting and presentation are conflicting. That’s why Betrand Meyer introduced the Command Query Separation principle. An architecture based on this principle combined with the Event Sourcing concept provides the ideal architecture for building high-performance systems designed using DDD. Well-known bloggers like Udi Dahan and Greg Young have already spent quite a lot of of posts on this, and this year’s Developer Days had some coverage as well. But how do you build such a system with the. NET framework? Is it really as complex as some claim, or is just different work?
Recommended
More Related Content
What's hot
What's hot(20)
Viewers also liked
Viewers also liked(8)
Similar to CQRS and Event Sourcing, An Alternative Architecture for DDD
Similar to CQRS and Event Sourcing, An Alternative Architecture for DDD(20)
More from Dennis Doomen
More from Dennis Doomen(20)
Recently uploaded
Recently uploaded(20)
CQRS and Event Sourcing, An Alternative Architecture for DDD
Editor's Notes
- DisadvantagesNo concurrency; conflicting service requests are simply rejectedStaleness ignored;Scalability limited; No domain verbs; domain model does contain concepts from the domain model, just not the business actionsGranularity DTOs; What operations to expose in your WCF service? What relations to include and when? What domain entities to flatten.Unneccesary DTO conversions; Conversions from/to domain model entities, traversing of relations, eager fatchingConflicting demands; query demands denormalized schema, commands require normalized integer schema
- DisadvantagesNo concurrency; conflicting service requests are simply rejectedStaleness ignored;Scalability limited; No domain verbs; domain model does contain concepts from the domain model, just not the business actionsGranularity DTOs; What operations to expose in your WCF service? What relations to include and when? What domain entities to flatten.Unneccesary DTO conversions; Conversions from/to domain model entities, traversing of relations, eager fatchingConflicting demands; query demands denormalized schema, commands require normalized integer schema
- Commands validate itself without using any context, thus is valid or not instead of sometimes.Commands are named in the Ubiquitous LanguageCommands can be send asynchronously, and thus can be resistent to database unavailabilityMogelijk meerdere commands met dezeflde state change: CorrectCustomerAddress, MoveCustomerCommand interfaces: in-memory, WCF, WCF RIA Services, NServiceBus, etc
- DisadvantagesNo concurrency; conflicting service requests are simply rejectedStaleness ignored;Scalability limited; No domain verbs; domain model does contain concepts from the domain model, just not the business actionsGranularity DTOs; What operations to expose in your WCF service? What relations to include and when? What domain entities to flatten.Unneccesary DTO conversions; Conversions from/to domain model entities, traversing of relations, eager fatchingConflicting demands; query demands denormalized schema, commands require normalized integer schema
- DisadvantagesNo concurrency; conflicting service requests are simply rejectedStaleness ignored;Scalability limited; No domain verbs; domain model does contain concepts from the domain model, just not the business actionsGranularity DTOs; What operations to expose in your WCF service? What relations to include and when? What domain entities to flatten.Unneccesary DTO conversions; Conversions from/to domain model entities, traversing of relations, eager fatchingConflicting demands; query demands denormalized schema, commands require normalized integer schema