Explore effective strategies for managing `Domain Events` in Spring Boot applications using MongoDB. Learn how to maintain data integrity when working with aggregates.
---
This video is based on the question https://stackoverflow.com/q/62534739/ asked by the user 'iam.Carrot' ( https://stackoverflow.com/u/3766231/ ) and on the answer https://stackoverflow.com/a/62535401/ provided by the user 'mtj' ( https://stackoverflow.com/u/5506086/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.
Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Domain Events with regards to Rollbak
Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.
If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Handling Domain Events in Spring Boot with MongoDB
In modern software development, managing domain events effectively is crucial. Particularly when working with Domain Driven Design (DDD) and databases like MongoDB, developers often face challenges around ensuring data integrity during operations involving multiple aggregates. This guide discusses a common scenario: creating two interdependent aggregates, and how to handle domain events to prevent inconsistent states.
The Challenge: Interdependent Aggregates
Let’s start by defining our scenario:
We have Service A, responsible for managing Aggregate A.
We have Service B, responsible for managing Aggregate B.
Whenever Aggregate A is created, we also need to create Aggregate B to maintain the relationship between them.
Problem Summary
The process is straightforward:
Aggregate A is created and saved in the database.
A domain event Aggregate_A_Created is fired.
An API call is made to the service that handles Aggregate B creation.
However, a problem arises if the creation of Aggregate B fails after the domain event has already been fired. The issue here is that:
Aggregate A is stored and the event is fired indicating its creation.
If the creation of Aggregate B fails, Aggregate A must be deleted to prevent inconsistencies, but now the system retains an event indicating that Aggregate A exists, potentially confusing other services.
Proposed Solution: Event Management Strategy
Handling this situation requires a thoughtful approach to how domain events are fired and managed.
1. Reconsider Aggregate Relationships
First, consider whether Aggregate A and Aggregate B should indeed be kept separate. If the business logic dictates a dependent relationship, it may be more prudent to treat them as parts of a common aggregate root. This can simplify event management since, if one aggregate fails, the other is not created independently.
2. Listening for Domain Events
If you decide that Aggregate A and Aggregate B must remain separate aggregates, implement an event listener:
Service B should listen for the Aggregate_A_Created event.
Only acknowledge the successful creation of Aggregate B in that listener. This way, there is no confusion about the state of Aggregate A unless Aggregate B creation is also successful.
3. Persistent Events Adequacy
Use a persistent event mechanism to ensure that if the system goes down after the creation of Aggregate A, the creation request for Aggregate B can still be processed adequately when the system is restored. This allows for eventual consistency, where the state can be recovered accurately.
4. Transaction Management with MongoDB
One of the frequent limitations developers face with Spring Boot and MongoDB is transaction support. Here’s a resolution:
Even though Spring may not provide transactional calls with MongoDB, remember that MongoDB itself can handle transactions. If Spring’s capabilities restrict your implementation, you can switch to using MongoDB's driver directly, which allows you to manage transactions more effectively. This lets you commit both Aggregate A and Aggregate B creations atomically.
Conclusion: Design for Integrity
By following these recommendations, you can better manage domain events in your Spring Boot application with MongoDB:
Reassess the relationships between aggregates.
Implement event listeners for Aggregate B creation.
Ensure persistence and adequate event handling for recovery.
Leverage MongoDB's native transaction handling when necessary.
Through strategic event management, you can maintain a consistent state across your services, enhancing the reliability of your application.
By adhering to these guidelines, your domain event system will be
Информация по комментариям в разработке