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A projection is used to create a highly performant read-model. It is eventually consistent. A cache is used when replaying all events to build up state is too slow. “It checks first in a cache and if the object is not present, it will check in the event store.” (https://hackernoon.com/1-year-of-event-sourcing-and-cqrs-fb9033ccd1c6) If the cache is present, it will grab the cache, apply the events since the caching to build up the current state....
Event Sourcing You are doing it wrong by David Schmitz ( https://www.youtube.com/watch?v=GzrZworHpIk ) Paper_ The dark side of event souring_ managing data conversion - Michiel Overeen, Marten Spoor, Slinger Jansen [[filing-learning-notes/article-effective-aggregate-design-part-i-modeling-a-single-aggregate-vaughn-vernon.md|]]Article_ Effective Aggregate Design - Vaughn Vernon Book_ Versioning in an Event Sourced System - Greg Young Book_ Exploring CQRS and Event Sourcing - Microsoft resources for eventsourcing resources for eventsourcing The dark side of event souring: managing data conversion - Michiel Overeen, Marten Spoor, Slinger Jansen [[filing-learning-notes/article-effective-aggregate-design-part-i-modeling-a-single-aggregate-vaughn-vernon....
Code snippets from GregYoung 8 CQRS Class - YouTube public class DeactivateInventoryItemCommand { public readonly Guid InventoryItemId; public readonly string Comment; public DeactivateInventoryItemCommand (Guid id, string comment) { InventoryItemId = id; Comment = comment; } void DeactivateInventoryItem(Guid, string comment) CommandHandler contains no logic, logic is in domain object delegates to domain object public class DeactivateInventoryItemHandler : Handles<DeactivateInventoryItem> { public DeactivateInventoryItemHandler(InventoryItemRepository rep){} void Handle(DeactivateInventoryItem cmd) { var item = repository.GetById(cmd.Id); item.Deactivate(cmd.Comment); } } Application Services cross-cutting concerns (logging, authentication)...
CQRS Documents - by Greg Young Events Column Type Comment AggregateId guid indexed, fk aggregates Data blob Version int unique within aggregate (UserId) guid (Timestamp) (CorrelationId) guid all events point to origin command (SequenceNumber) long auto-incrementingeventstore as queue Aggregates Column Type Comment AggregateId guid indexed, fk aggregates Type varchar fully qualified name Version int denormalized from Events Read event Select * from events where AggregateId =? Order by version Write event...
high level CQRS and Event sourcing client commands write / domain events read model dtos client
Code snippets from GregYoung 8 CQRS Class - YouTube public class DeactivateInventoryItemCommand { public readonly Guid InventoryItemId; public readonly string Comment; public DeactivateInventoryItemCommand (Guid id, string comment) { InventoryItemId = id; Comment = comment; } void DeactivateInventoryItem(Guid, string comment) CommandHandler contains no logic, logic is in domain object delegates to domain object public class DeactivateInventoryItemHandler : Handles<DeactivateInventoryItem> { public DeactivateInventoryItemHandler(InventoryItemRepository rep){} void Handle(DeactivateInventoryItem cmd) { var item = repository.GetById(cmd.Id); item....
GregYoung 8 CQRS Class ( https://www.youtube.com/watch?v=whCk1Q87_ZI ) Code snippets from GregYoung 8 CQRS Class - YouTube original Code snippets from GregYoung 8 CQRS Class - YouTube
Course: CQRS in Practice (https://app.pluralsight.com/library/courses/cqrs-in-practice) CQRS & Onion Architecture Map CQRS & Onion Architecture where do C, Q, E belong? Map where do C, Q, E belong? Where to put Command Handlers Map Where to put Command Handlers Command reuse -> domain service Map Command reuse -> domain service Domain Service called for duplicate code Projections Map Choosing projection type A - database triggers...
Greg Young — A Decade of DDD, CQRS, Event Sourcing ( https://www.youtube.com/watch?v=LDW0QWie21s )
Greg Young - CQRS and Event Sourcing - Code on the Beach 2014 https://www.youtube.com/watch?v=JHGkaShoyNs Notes: test without getters: 3:28:20 / 6:31:00 don’t care about state if I call ‘Deactivate’ twice, I get an exception that’s the invariant VERSIONING Event Versioning: 4:24:22 / 6:31:00 add both methods in aggregate upcasting old to new event When do we need to versionize events? -> when they were written to production dev? just throw away your local event log...