Questions tagged [cqrs]

Command Query Responsibility Segregation design pattern

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How to maintain workflows in event sourcing architecture

We're doing a microservice architecture with CQRS and event sourcing. Regular command servers have no persistent memory - when a command enters, if they want to verify it against an aggregate, they ...
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26 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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1answer
75 views

Designing frontend experience to support backend async CQRS operations

I'm developing a microservice with CQRS and Event Sourcing. When an event is saved to the event store, the service currently also saves the updated aggregate root as a JSON object in a separate table. ...
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169 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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92 views

Modify Command object inside decorator of CommandHandler(CQRS) or any other practice for avoiding duplication

Currently, we have multiple commands which share two same properties (BookName and ShopId). While handling those commands those properties must be validated with the help of some service. Let's say ...
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1answer
106 views

Determining an appropriate use case for CQRS

I'm building an application which lets users view a large amount of data about a single single entity (lets say it displays a users health profile for the day) via a single webpage. The data comes ...
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37 views

Event sourcing and state set event

I'm trying out commanded framework for Elixir that implements event sourcing and CQRS (it have abstract structure of command, command middleware, router, aggregate, process manager, projection and ...
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59 views

Is one to one mapping necessary between Write Applications and Read Applications

Introduction: We have a bunch of micro services (about 40) to serve our customers. To facilitate scaling and audit-ability of selected few micro services we have decided to redesign them using CQRS ...
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100 views

DDD Monolith eshop architecture based on multiple BoundedContexts Question

I´m creating my first eshop / CMS based on DDD / CQS concepts. I want to create application using BoundedContexts separtion as modular monolith at the first stage and maybe latter extract some BC as ...
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1answer
224 views

Reducing the code duplication between read and write application in CQRS

I am building an application and trying to embrace Domain Driven design principles, CQRS and event sourcing. We are having two applications one for reading and another for writing. The write ...
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1answer
61 views

ES/CQRS: How to access additional information in projections

I'm developing an event-sourced/CQRS application and do not understand the best strategy to use when building the read model projections when additional domain data is needed. A partial representation ...
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2answers
189 views

Dealing with property-level permissions in DDD and should UI or authorization influence the domain model?

Suppose I have a command like below: public sealed class UpdateExampleCommand { public int Field1 { get; set; } public string Field2 { get; set; } public bool Field3 { get; set; } ...
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Commiting transaction in the repository instead of the application service

After quite some time thinking about it, and testing both methods, I'm really struggling with choosing the right manner to commit my transactions. To shape the context, we are in the context of ...
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1answer
40 views

How specific should administrative compensating events be in a CQRS/ES system?

Are there any best practices around how specific to make events that are generated administratively, say to clean up after one-off operational issues? For example: Say you have a credit card ...
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3answers
214 views

How to deal with UI data requirements in DDD

I'm using DDD and a CQRS/Event Sourcing architecture so my domain logic is separated in a microservice (e.g: command service) and the read side is in another microservice (e.g: query service). We ...
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1answer
92 views

Is it overkill to use event sourced actor model with message queue which send commands from gateway?

The gateway uses Rabbitmq with Masstreansit to send commands to services. Some of services require event sourcing in their internal architecture. Since I need my aggregate states available, and the ...
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1answer
152 views

What is the most appropriate way to launch an API gateway on a massive domain?

We're trying to develop a comprehensive system which has broken down to multiple microservices. So we decided to use CQRS and DDD to tackle the complexities of the domain. Also we’re about to launch ...
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Should perform query at the point of time for the event or the actual time when working with CQRS for queue system?

I'm trying to implement CQRS for a queue system where user can join a queue by clicking a button. The system will tell the user if queue is full. When the user click the button, it raised the ...
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1answer
95 views

How to split Aggregate Root that have equal identity?

In DDD, creating smaller aggregates is encouraged where possible, but in a system we are designing we are running into an issue regarding the identity of aggregates. The system evolves around ...
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1answer
617 views

CQRS and GraphQL

Context Domain I have a CQRS domain with requests, authorizers, handlers, response objects, entities, filters, pagination. It only depends on: external services (email, other APIs, etc...) a ...
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In a DDD CQRS API, is it preferable to have a separate DTO per query or per representation of a resource?

I am in the middle of starting up a new project and just wanted some reassurance as to which approach to DTO's returned by the read-side was easier to maintain in a real world application with ...
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1answer
96 views

DDD and CQRS - Define an entity for Scheduling use case

I have a use case of scheduling a person to some work for some time range. Eg. A service for assigning a person A to work for time range X to Z in location C. The only constraint it has, is one ...
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75 views

How to check if the command is execuable when it delivers through asynchronous message queue?

The aggregate root's state is the product of the commands it receives. So different order of receiving the commands produce different aggregate root states. How can I check domain rules based on the ...
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169 views

What's the use of event sourcing and asynchronous message queues for sending commands

In short: Out of order commands end up with out of order events, so does the ordering of the events matter in such situations? Since we are uncertain about the order of commands when an asynchronous ...
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266 views

CQRS sequential numbering of business documents

I am currently building a microservice-based system to learn CQRS/ES, Docker, AMQP and all the other goodies that goes with it. I have never asked a question online before as I am usually pretty good ...
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55 views

Same events for different aggregates in CQRS?

I'm developing an application using CQRS + ES. Now I have 2 aggregates which are technically almost exactly the same, only they are different concepts in the domain. Therefore I will separate them ...
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1answer
142 views

How to handle Domain Event handlers ordering

Background: we have 2 bounded context: Inventory and Sale application context is Point-of-sale system Scenario: When a Checkout happen on Sale BC, we would like to decrease quantity in Inventory. ...
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65 views

Storing within the domain or use CQRS?

Assume we're building a fleet management system that is monitoring telemetry on a fleet of cars. Important telemetry include like location, speed and engine temperature. Metrics are mostly dynamic and ...
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143 views

Is it a bad practice or uncommon to save “Invalid operation attempted” events in an Event Store when doing Event Sourcing?

I have a simple toy project that deals with Banking operations (cash deposit, withdrawals, wire transfers, open and close accounts). I am wondering whether there is something wrong about saving ...
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1answer
100 views

Are separate controllers used when adopting full scale CQRS?

I understand there are three flavours of CQRS: 1) Separate models only i.e. a domain model and a read model. 2) separate models and repositories. 3) Separate models; repositories and physical ...
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132 views

Can a query handler (not repository) access a web service?

Say I have the following class, which maps to a database table: public class Person { public Guid Id {get; set; } public string Name {get; set; } public DateTime DateOfBirth {get; set; } public ...
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1answer
74 views

How to approach to ES/CQRS in serverless cloud?

Let's say I want to use CosmosDB for Event Store, where have single collection for all events. Currently it is not horizontally partitioned, but it is a possibility for future. Now, I need to ...
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476 views

EventSourcing / CQRS Implementation with ASP.NET Core WebApi and Azure Cosmos DB

I was looking for an easy implementation of the Event Sourcing and CQRS Pattern in ASP.NET Core using Azure Cosmos DB as Event Store. As I couldn't find anything appropriate I decided to write a ...
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180 views

CQRS and Transactional Event Sourcing, problem while recreating Read DB

I'll first explain the context of my problem. The backend of my current project is using DDD, CQRS and Event Sourcing as a stack (the read DB being a MongoDB, my write DB being an event store). At ...
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1answer
277 views

CQRS - Business Logic in Query Side

I am working on handling authorization for an application. I need some way for a command handler to ask the Authorization bounded context "Is this user allowed to perform this action?". User account ...
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37 views

How many exchanges when using scatter gather and CQRS?

I am trying to learn more about CQRS and enterprise integration in my spare time. I have created an application, which uses CQRS and the Scatter Gather Pattern. There are two web APIs for the CQRS ...
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43 views

Can the read api receive events that the write api does not receive or raise?

Say I have a read API and a write API: MyApp.Write.api MyApp.Read.api Both API's handle integration events from other apis/microservices. Say I had certain integration events that only need to be ...
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1answer
952 views

CQRS command that needs to work with multiple aggregate roots

I have have a business process that receives an order request which also includes full customer information. In the cases where the external customer ID from that order request is not found in our DB,...
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1answer
117 views

Passing Keys instead of Messages

Recently I stood up a Redis server and tested the idea of storing application 'states' that only existed in our application and were never stored in our database. Don't know if we will ultimately do ...
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1answer
176 views

Circuit Breaker + Retry - Repository or Application Layer

I currently have a Web App using ASP.NET Core 2.2, Domain Driven Design, Clean Architecture, and CQRS. I'm using MongoDB as persistence. I have developed a Repository pattern to abstract the MongoDB ...
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2answers
783 views

DDD - Modifying multiple entities under multiple aggregate roots

In our domain we have a concept of billable activities that get logged by a user. The modeling is pretty straightforward -- the User is an aggregate root, with the Activities being a collection under ...
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1answer
432 views

CQRS with an Event Log and without Event Sourcing

I am trying to understand the difference between an event log and event store in the context of event sourcing. A really nice explanation I found is that an event store is the single source of truth ...
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1answer
278 views

is Event sourcing using Database CDC considered good architecture?

When we talk about sourcing events , we have have a simple dual write architecture where we can write to database and we can write the events to a queue like Kafka . Other downstream system can read ...
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1answer
143 views

DDD - Aggregate that changes “owner” mid-process

We're evaluating CQRS/ES for a high-volume subsystem in our app in order to take advantage of distributed systems and ensure uptime. This is my team's first time implementing this architecture, and I'...
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1answer
145 views

What is the full value of the CQS principle in a system that doesn't implement the CQRS pattern?

I'm having trouble grasping the value proposition of the "command" half of the CQS principle in a system that doesn't implement command query responsibility segregation. The CQS principle states that ...
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3answers
635 views

Domain Events, CQRS, and dependency resolution in handlers

Currently: ASP.NET Core 2.2. I've been doing quite an extensive research in this topic (Domain Driven Design used together with Clean Architecture): DDD: Where to place domain event handlers? And I'...
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1answer
141 views

Can the write database have different fields to the read database?

I am trying to learn CQRS in my spare time. Say I have a class like this: public class Person { private Guid Id {get; set;} private Guid Name {get; set;} private List<Order> orders; //...
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279 views

Anemic Domain Model, CQRS, command bus

Considering this pattern is used to support CQRS message bus, examples are buslane Python or MessageBus PHP It uses commands to change the domain model, and publishes domain events This looks great ...
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1answer
194 views

How to better scale reads in a website: to CQRS or not to CQRS?

The company i'm working for it's rewriting a legacy web application and we are evaluating the better architecture to get the job done. The business domain is quite simple: there are few entities, ...
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2answers
1k views

CQRS using queries or read services only?

Discussing about a CQRS implementation with my team we don’t agree on a point concerning the Query side. On the Commad side we have actual command clases; a CommandDispatcher that schedules commands, ...