Questions tagged [event-sourcing]

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Event Driven Architecture: FIFO queues vs event versions

A common problem with eventing (or messaging) is ordering events. For example a resource is updated twice. An event is emitted for each update. In order to ensure consistency, the consumer must not ...
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3answers
126 views

Coping with lack of infinite retention event broker in event driven architecture

I am reading “Building Event Driven Microservices”. It states a requirement of the event broker is: Infinite retention: Event streams must be able to retain events for an infinite period of time. ...
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1answer
60 views

Event Sourcing inside a RDBMS

I'm thinking about using an Event Sourcing / Event Store pattern in my RDBMS designs. What I mean by Event Store is a pattern where each data mutation (INSERT / UPDATE / DELETE) is persisted as an ...
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56 views

Saga / Processmanager?

I'm thinking about this scenario: I can receive customer inquiries by Email. Those inquiries can be sent from existing customers or unknown "customers" - I'll call latter "Leads". ...
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2answers
99 views

Event Sourcing questions

I have a question regarding the architecture of microservices and event sourcing. Imagine that I have the User service and the Franchise service. In the Users entity on the user service I have an ...
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1answer
80 views

Are RabbitMQ Streams overkill for 1 machine event-driven architecture aplication?

If developing event-driven application(more precisely event sourcing application) that will run solely on 1 machine are RabbitMQ Streams an overkill, or maybe a misfit? In theory RabbitMQ Streams seem ...
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47 views

How to identify an event stream?

I recently started discovering event sourcing so I am fairly new on the subject. Imagine having a system (system A) which listens to events of a third party order service (system B). These events can ...
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2answers
130 views

In CQRS/ES should database calls be done in command handlers or domain models?

In the context of a DDD application following CQRS and the event sourcing pattern, I have 2 questions. At which layer should be made the direct calls to the Infrastructure layer? At the Application ...
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149 views

Implementation of projections in event-sourced system

I'm working on a application which uses event-sourcing and CQRS to define it's domain model. Background We have implemented projections to aggregate stream of all domain events into a read models used ...
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2answers
77 views

How to build an event sourced system with AWS (Specifically, how to deal with side effects)

So the current setup is a typical event sourced system built on AWS: Lambdas exposed with API Gateway to get the orders (commands), the domain (aggregates) apply some validations after loading the ...
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1answer
72 views

In CQRS/ES where does an Aggregate Root belong?

Disclaimer: This question may be related to the framework I'm using to support CQRS/ES rather than the concepts themselves but many of these frameworks implement the same strategies, making me think ...
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1answer
77 views

How do I implement a domain entity behaviour that depends on some external infrastructure?

I am in the process of developing some software using CQRS, ES and DDD. A part of the system is writing services for controlling devices and collecting data from them. Consider a "Start" ...
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3answers
181 views

How can I coordinate updating multiple Aggregates as a result of one command, without introducing exploitative possibilities?

I'm trying to figure out how to integrate one command that updates multiple Aggregates in different contexts in a video game. The components/considerations for my particular design are DDD, CQRS, ...
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1answer
70 views

What is the relationship between Event Store and Persistence Mechanism when designing Aggregate + Event Sourcing?

I'm trying to implement an Event Store, to be used with Aggregate+Event Sourcing (A+ES), and I've run into I think a gap in understanding. I'm reading Implementing Domain Driven Design, using both the ...
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86 views

Outbox pattern in a monolith with NoSQL?

As I have come to understand, there is generally two ways of ensuring atomicity of both domain events and state changes to aggregate roots in order to achieve at least once delivery of events--the ...
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2answers
123 views

How can we update potentially many Read Model Projections based on an Event that is not within the native context?

I have a Shop which sells Items for a given Price. To be clear, this is in the context of a video game, not an enterprise ERP system. The game operator can create Shops that Players can use to buy ...
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2answers
227 views

In an event sourced system, how do I get a current state of an entity?

Let's assume I use Kafka as an event store and put there all the lifecycle events of an order. Now I need to get the current state of this order in my system in during some business process. What's ...
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2answers
367 views

In DDD Aggregate + Event Sourcing, do Events happen before or after state changes?

Part of the Aggregate + Event Sourcing (A+ES) methodology feels uncomfortable. Why does it feel uncomfortable? (As I've read from other questions and the book itself, it's a new-ish way of thinking, ...
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2answers
130 views

Event sourcing: Does it make sense for immutable entities?

I'm on a project which often follows the trends, so whatever works for big cool companies, will surely work for us, regardless the contexts and specifics. If that sounds like a little rant, then it is....
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1answer
266 views

Upholding business logic and invariants in an event sourced CQRS architecture

My understanding of a CQRS architecture is that a micro-service is split to two servers each with its own database such that the first server handles all the writes and the second server handles all ...
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1answer
92 views

Event sourced persistence and data model refactoring

I've been working on a system that is using event-sourced persistence for it's data model. It is using a standard model of sequence of events with aggregates being rehydrated from those events and ...
2
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1answer
209 views

Event Sourcing - More complex example

Usually when I read Event Sourcing examples - they are pretty simple. When trying to implement something even more complex - it seems to get pretty ugly pretty quickly. Let me explain this on one ...
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2answers
173 views

Event sourcing with concurrency against projections

I'm using event sourcing in an application and constantly find a problem for which I do not find a good solution. In this scenario we have an application for a hair stylist. We have a ...
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64 views

Strategy for a worker microservice to communicate with GraphQL API

I am trying to find the best way for a microservice to communicate with GraphQL Basic scenario: Client subscribed to GraphQL via Subscriptions (WebSockets) Client creates an Item using Mutation which ...
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121 views

How to save to database and publish atomically? ( all or none )

I'm trying to implement microservice architecture to our application (basically an ecommerce) and one of the challenges that I can't really find a good answer for (despite being so many similar ...
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1answer
293 views

Communication between services in a microservices architecture, is direct communication okay?

I've been reading a lot on why one should use messages (w/ event sourcing/CQRS) for microservices communication and I get it. But most of the stuff I read online state that the main reason for using ...
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2answers
372 views

Primitive obsession, value objects, Commands, Events and where to convert

I tried to combine two rules. Don't fall to primitive obsession (e.g. EMailAddress should be a value object in domain objects and not a string). Don't use value objects in commands and events.1, 2, 3 ...
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1answer
89 views

How to get Address pincode inside Customer class

I have 2 domains Customer and Address using using EventSourcing and CQRS in our Monolithic app, below is my query: Customer Domain: class Customer { //Aggregate class String custId; ...
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1answer
78 views

designing events for an event sourcing based application

In an application to handle employee leaves, I decided to try CQRS & event sourcing and came up with the following flow of events. app events leave-application-received leave-application-...
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3answers
955 views

Event Sourcing - Multiple events or a single for a change on one aggregate?

I have a checklist system where we are implementing CQRS/ ES (Event Sourcing). We have a command updateStatus(taskId: string, status: boolean) to mark a task or sub task as completed. If I receive a ...
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1answer
135 views

Event sourcing: Update local data before posting an event?

We are introducing events to our system (I would hesitate to call it 'event sourcing', but we have started down this road). To do this we are still maintaining the same HTTP public 'CRUD' API's, but ...
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1answer
176 views

Event Sourcing/CQRS for Self-Related Entities

I'm building a platform that has an entity named content. There's a clear boundary around what defines content except that it can have relationships with other content entities. Up until now, there's ...
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1answer
127 views

Options for building initial event sourcing projection when you cannot go back to the beginning of the history

I’m building a microservice which depends on a set of downstream services to collect the data necessary to operate. It is a data delivery system, I’m not source of truth for any data, my system rather ...
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3answers
1k views

What are the problems with command handlers returning data in CQRS?

I have a system using CQRS/ES, where: The command handlers are actually implemented as an application service layer, which executes synchronously. I.e. events are persisted in the event store before ...
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1answer
183 views

DDD - Concurrency and Command retrying with side-effects

I am developing an event-sourced Electric Vehicle Charging Station Management System, which is connected to several Charging Stations. In this domain, I've come up with an aggregate for the Charging ...
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2answers
242 views

Merging aggregates with Event sourcing

I'm currently evaluating Event Sourcing and CQRS for an implementation of a new business requirement at my day job. While I can't really speak about the actual business problem, I can give a few ...
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2answers
60 views

Event Sourcing Architecture: Ingesting event data from Phones

We will be streaming data from Phones (<= 5000) to a server. We were previously sending the data using MQTT to AWS IOT. Now we want to run this locally. Estimated size per second to be ingested is ...
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3answers
1k views

How does "event triggers event" really work in Event Sourcing / CQRS?

After reading/watching a lot about Event Sourcing, there is one thing I don't fully understand: Events that lead to triggering of other events. Let's take StackExchange's "close question" feature as ...
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2answers
77 views

How to call the API once per event-message?

I have X number of servers in NLB listening to an event that gets published by a backend system. I am planning to develop a windows service that listens to the event and then calls an internal API. ...
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3answers
6k views

Which comes first: event or the change?

I've been researching Event Sourcing, and it seems there are two philosophies hidden within what I've read. The core difference is whether actors in the system are proactive, making changes first and ...
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1answer
149 views

Are there any pitfalls to having multiple handlers for a command?

We're looking to split up a monolith. In order to do so, we've identified some business areas that look like good candidates for subdomains, and we're trying to figure out how to split the ...
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2answers
87 views

Should I create one large initial event or break down in smaller events?

I'm experimenting with event sourcing for an application we haven't build yet. No, I won't implement this without any thought, I'm just experimenting. My domain model looks somewhat like this. The ...
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1answer
1k views

Event sourcing and sync between write and read model

I am creating this project based on event sourcing and cqrs. My write and read model are on different databases (and machines) and are connected through an event bus (in particular I am using ...
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5answers
268 views

Effective methodology in designing event driven systems

I understand "the works" of event driven systems and I've built simple ones. However I find that I am struggling a bit in efficiently designing one. E.g., Formulating all the events upfront seems not ...
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1answer
123 views

Decoupling from third party library

I'm doing a project in PHP and I'm implementing Aggregates and Event Sourcing. In order to avoid coding up all the logic related with ES myself I've decided to use a third party library called ...
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1answer
83 views

ActiveMQ for event driven architecture

I am using ActiveMQ and I have a scenario where I need to update the event for 100 consumers parallelly. I am looking for a solution where the 100 consumers receive the event parallelly (i.e there ...
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2answers
238 views

Should microservices in an event sourced architecture not communicate directly with one another via REST/gRPC/etc?

I'm trying to wrap my head around event sourced architectures. It seems like common advice is to have small events with as little info in them as possible (opposed to large events with everything in ...
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1answer
193 views

Event Sourcing, state in events vs state in projections

I would like to ask what is the preferred way of passing additional state to projections. I have UserAggregate that is watching changes of several attributes of user (for instance address, name and ...
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0answers
454 views

Design of Spring boot endpoint that returns large amount of data continously until complete

I'm developing a web application using Spring Boot and React, that needs to return information about hotels from different cities: As an input of the controller, I receive a list of cities that can ...
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3answers
1k views

CQRS - How can a command properly validate when queries are required?

I'm aware that this question has been asked several times, but I have some concerns regarding querying from the write side that I don't see addressed in the already existing questions, more ...

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