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opencqrs

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Java CQRS/ES Framework for the EventSourcingDB

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# Installation Guide

1. Get the code

git clone https://github.com/open-cqrs/opencqrs

Downloads the entire project code from GitHub to your computer.

cd opencqrs

Moves into the project folder you just downloaded.

2. Docker

Easy Recommended

Prerequisites

Git Needed to download the project code from GitHub.
Docker Desktop Needed to build and run containers. Install it and keep it running in the background.

docker compose -f example-application/docker-compose.yml up -d --build

Runs the command against the services defined in the compose file.

✅ Run docker compose ps to check the containers are Up. If the README mentions a port, open http://localhost:PORT in your browser.

3. Gradle (Java/Kotlin)

Medium

Prerequisites

Git Needed to download the project code from GitHub.
JDK (Java) Required to build and run Java/Kotlin projects.
Gradle If the repo includes gradlew (Gradle Wrapper), you don't need to install Gradle separately.

./gradlew build

Builds the project using Gradle.

✅ A BUILD SUCCESSFUL message means it worked. The output is created under build/.

// repository documentation

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# OpenCQRS - Java CQRS/ES Framework for the [EventSourcingDB](https://www.eventsourcingdb.io)

[![Maven](https://img.shields.io/maven-metadata/v.svg?color=yellow&label=Maven%20Central&logo=apachemaven&metadataUrl=https%3A%2F%2Frepo1.maven.org%2Fmaven2%2Fcom%2Fopencqrs%2Fframework%2Fmaven-metadata.xml)](https://central.sonatype.com/namespace/com.opencqrs)
[![Java](https://img.shields.io/endpoint?url=https%3A%2F%2Fraw.githubusercontent.com%2Fopen-cqrs%2Fopencqrs%2Frefs%2Fheads%2Fgh-pages%2Fbadges%2Fjdk.json)](https://openjdk.org)
[![EventSourcingDB](https://img.shields.io/endpoint?url=https%3A%2F%2Fraw.githubusercontent.com%2Fopen-cqrs%2Fopencqrs%2Frefs%2Fheads%2Fgh-pages%2Fbadges%2Fesdb.json)](https://www.eventsourcingdb.io)
[![Spring Boot](https://img.shields.io/endpoint?url=https%3A%2F%2Fraw.githubusercontent.com%2Fopen-cqrs%2Fopencqrs%2Frefs%2Fheads%2Fgh-pages%2Fbadges%2Fspring.json)](https://spring.io/projects/spring-boot)
[![JavaDoc](https://img.shields.io/badge/JavaDoc-click%20here-lightgrey?logo=readthedocs)](https://docs.opencqrs.com/javadoc)
[![Documentation](https://img.shields.io/badge/Documentation-click%20here-blue?logo=materialformkdocs)](https://docs.opencqrs.com)

![OpenCQRS](https://raw.githubusercontent.com/open-cqrs/opencqrs/main/banner.png)

OpenCQRS is a lightweight open source Java framework for building applications based on the CQRS (Command Query Responsibility Segregation) and Event Sourcing patterns.
It includes built-in support for testing and offers optional Spring Boot integration to simplify configuration and production deployment.
OpenCQRS is based on [EventSourcingDB](https://www.eventsourcingdb.io), a third-party event store, and provides a Java client SDK for it.

## Installation

OpenCQRS is available directly from [Maven Central](https://www.maven.org). A [running instance](https://docs.eventsourcingdb.io/getting-started/running-eventsourcingdb/) of the
[EventSourcingDB](https://www.eventsourcingdb.io) is required as event store. Spring Boot developers must add the following dependencies to their project in order to start developing
and testing OpenCQRS applications:

### Maven (pom.xml)

```xml
<dependencies>
    <dependency>
        <groupId>com.opencqrs</groupId>
        <artifactId>framework-spring-boot-starter</artifactId>
        <version>{{version}}</version>
    </dependency>
    <dependency>
        <groupId>com.opencqrs</groupId>
        <artifactId>framework-test</artifactId>
        <version>{{version}}</version>
        <scope>test</scope>
    </dependency>
</dependencies>
```

### Gradle (build.gradle.kts)

```kotlin
dependencies {
    implementation("com.opencqrs:framework-spring-boot-starter:{{version}}")
    testImplementation("com.opencqrs:framework-test:{{version}}")
}
```

Make sure to configure a proper Spring Boot application name and the connection settings for the
event store, i.e. within your `src/main/resources/application.yml`:

```yaml
spring.application.name: sample-app

esdb:
  server:
    uri: http://localhost:3000
    api-token: <secret>
```

## Usage

OpenCQRS provides the following core capabilities to support the development of robust CQRS/ES-based systems:

### Command Handling

Define annotation based command handlers for implementing business logic and publishing new events:

```java
public record PurchaseBookCommand(String isbn, String author, String title, long numPages) implements Command {

@Override
    default String getSubject() {
        return "/book/" + isbn();
    }
}

public record BookPurchasedEvent(String isbn, String author, String title, long numPages) {}

@CommandHandlerConfiguration
public class BookHandling {

@CommandHandling
    public String purchase(PurchaseBookCommand command, CommandEventPublisher<Book> publisher) {
        publisher.publish(
                new BookPurchasedEvent(command.isbn(), command.author(), command.title(), command.numPages()));

return command.isbn();
    }
}
```

### State Rebuilding

Define annotation based state rebuilding handlers for reconstructing command model state:

```java
public record Book(String isbn, long numPages) {}

@CommandHandlerConfiguration
public class BookHandling {

@StateRebuilding
    public Book on(BookPurchasedEvent event) {
        return new Book(event.isbn(), event.numPages());
    }
}
```

### Testing Command Logic

Test command handling logic using the built-in test fixture support:

```java
@CommandHandlingTest
public class BookHandlingTest {

@Test
    public void canBePurchased(@Autowired CommandHandlingTestFixture<PurchaseBookCommand> fixture) {
        fixture.given()
                .nothing()
                .when(new PurchaseBookCommand("4711", "JRR Tolkien", "LOTR", 435))
                .succeeds()
                .allEvents()
                .exactly(new BookPurchasedEvent("4711", "JRR Tolkien", "LOTR", 435));
    }
}
```

### Event Handling

Handle events asynchronously to decouple side effects:
```java
@Component
public class BookCatalogProjector {

@EventHandling("catalog")
    public void on(BookPurchasedEvent event) {
        // ...
    }
}
```

### Looking for runnable examples?

Check out our [OpenCQRS Sample Applications](https://github.com/open-cqrs/opencqrs-samples) repository.
It provides working example projects that demonstrate how to build applications using OpenCQRS.

## Project Contents

This is a multi-module project. It contains the following modules:

| module                                                                         | description                                                                     |
|--------------------------------------------------------------------------------|---------------------------------------------------------------------------------|
| [esdb-client](esdb-client)                                                     | Client SDK for the [EventSourcingDB](https://www.eventsourcingdb.io)            |
| [esdb-client-spring-boot-autoconfigure](esdb-client-spring-boot-autoconfigure) | Spring Boot auto configurations for the ESDB client SDK                         |
| [esdb-client-spring-boot-starter](esdb-client-spring-boot-starter)             | Spring Boot starter for the ESDB client SDK                                     |
| [framework](framework)                                                         | CQRS/ES core framework (depends on esdb-client)                                 |
| [framework-spring-boot-autoconfigure](framework-spring-boot-autoconfigure)     | Spring Boot auto configurations for the CQRS/ES framework                       |
| [framework-spring-boot-starter](framework-spring-boot-starter)                 | Spring Boot starter for the CQRS/ES framework                                   |
| [framework-test](framework-test)                                               | CQRS/ES framework test support with optional Spring support                     |
| [example-application](example-application)                                     | A complete library domain example application based on OpenCQRS and Spring Boot |

## License

This project is licensed under Apache 2.0 – see the [LICENSE file](LICENSE.txt) for details.

## Copyright

Copyright (C) OpenCQRS and contributors. All rights reserved.

## Contributions

We welcome contributions to OpenCQRS!
To ensure a smooth process and consistency with the project's direction, please contact us before starting work on a feature or submitting a pull request. This helps avoid duplicate efforts and ensures alignment.

Feel free to open issues or reach out via email – we’re happy to collaborate.

## Contact

For questions or feedback, please contact the development team at
[opencqrs@digitalfrontiers.de](mailto:opencqrs@digitalfrontiers.de).