Separating data and behaviors can have a pretty profound impact on your design. An Event Sourced Aggregate allows you to focus on business logic by having capabilities to produce data (Events). Event Sourcing does exactly this by limiting the amount of state you require only to that needed for business logic within an Aggregate.
Value Objects are a part of Domain-Driven Design, and Julie Lerman and I cover them in our DDD Fundamentals course on Pluralsight. Even if you're not applying Domain-Driven Design to your application, you can take advantage of refactoring your business classes to avoid code smells like primitive obsession (follow the link for more on refactoring and code smells). To demonstrate this concept, I'm going to show a simple class as it might start out, and then show how I would refactor it. (This is actually based on a conversation I just had with one of NimblePros' clients. I figured I might as well share my thoughts more broadly than just with that team! The actual types have been changed, but the principles can be applied generally.)
In distributed software applications, different services or processes or apps frequently need to communicate with one another. Modern architectural trends toward microservices and containers and cloud-native apps have all increased the likelihood that apps will increasingly be deployed not as single monoliths, but as collections of related services. There are only so many different ways these applications can communicate with one another, and each choice brings with it certain benefits as well as consequences and tradeoffs. Let's consider the options and assess each one based on its relative performance, scalability, app isolation or independence, and complexity. Also, if you're interested in this topic, you may also want to read about how to apply CAP theorem (and PACELC) to microservices.
I think its fair to say that "microservices" has established itself as the leading way to architect a modern distributed cloud-native application. I've discussed many of the advantages of this approach over "monolithic" architectures in my Pluralsight courses such as Microservices Fundamentals...
In the last post, we looked at our procedural handler and pulled behavior out that called to external services into its own domain service. This let our handler become more unit testable by creating a test seam, and we could now alter the behavior of the abstraction through mocks/stubs etc.
In my last post, we looked at the Compose Method refactoring as a means of breaking up long methods into smaller ones, each with an equivalent level of granularity. This is the refactoring in my applications I tend to use the most, mainly because it's the simplest way of breaking up a hard-to-understand method.
What is CQRS? Traditional Software Development data models, which appear to indicate or infer that reads and writes are in synchronization when it comes to interacting with the database, in order to maintain the ACID( Atomicity, Consistency, Isolation, Durability) properties pertaining to the data.
消息队列中间件（简称消息中间件）是指利用高效可靠的消息传递机制进行与平台无关的数据交流，并基于数据通信来进行分布式系统的集成。 通过提供消息传递和消息排队模型，它可以在分布式环境下提供应用解耦、弹性伸缩、冗余存储、流量削峰、异步通信、数据同步等等功能，其作为分布式系统架构中的一个重要组件，有着举足轻重的地位。 目前开源的消息中间件有ActiveMQ、RabbitMQ、Kafka、RocketMQ、pulsar等，在整体架构中引入消息中间件，势必要考虑很多因素，比如成本及收益问题，怎么样才能达到最优的性价比？虽然消息中间件种类繁多，但是各自都有各自的侧重点，选择合适自己、扬长避短无疑是最好的方式。
How do you test your domain when Event Sourcing? I find testing aggregates with Event Sourcing to be simpler than testing if you’re storing the current state. The inputs to your aggregate are events and the output of your aggregate are events.
The term “Event” is really overloaded. There are many different utilities that leverage events. Event Sourcing, Event Carried State Transfer, and Event Notifications. None of these are for the same purpose. When talking about an Event Based architecture, realize which one you’re using and for what purpose.
DDD是近年软件设计的热门。CQRS与Event Sourcing作为实施DDD的一种选择，也逐步进入人们的视野。围绕这两个主题，软件开发的大咖[Martin Fowler]、[Greg Young]、[Udi Dahan]分别有所论述，[MSDNC QRS Journey]、[Implementing DDD]、[Patterns, Principles, and Practices of DDD]等著述也提供了范例，国内外各大论坛的文章和DDD开源框架更是数不胜数，为学习CQRS和Event Sourcing提供了大量指导。其中，Greg Young的论文最为系统。故本文通过解读其论文，简单梳理了CQRS与Event Sourcing的发展脉络，厘出其中的主要技术重点，并提出以Akka作为落地方案，以求对这两个主题有一个较为全面的总结。错谬之处，还望指正。
In previous posts in this series, I covered what a Modular Monolith is, what its architecture looks like and how this architecture can be enforced. Then I described architectural drivers for this architecture and styles of integration between modules. In this post I would like to go deeper – a level lower and describe how such architecture can be designed. We are not going to implement this architecture yet – we will focus on its technology-agnostic design.
Although Command Query Responsibility Segregation (CQRS) seems to be a term a lot of developers are aware of, I do think the majority have the wrong definition. Like many terms in the software development industry, things over time get confused, and then those confusing ideas propagate. These are the 3 CQRS Myths I see or hear the most often.
Domain events are one of my favorite patterns and one Julie Lerman and I cover in our DDD Fundamentals course, on Pluralsight. I differentiate between two kinds of domain events: pre-persistence and post-persistence. You'll find a good implementation of post-persistence domain events (using MediatR) in my Clean Architecture solution template. However, until recently, I hadn't built an immediate, pre-persistence implementation of domain events for .NET using MediatR. This is meant to follow a similar approach to Udi Dahan's classic static helper, which relied on StructureMap and static methods.
ElasticSearch是一个用Java语言开发的分布式文档检索引擎。也支持文档存储功能,且不会将信息类似SQL存储为列数据,而是存储已序列化的JSON文档的复杂数据结构。而且ElasticSearch支持集群部署,当集群中有多个ElasticSearch节点时,存储的文档会分布在整个集群中,并且可以从任何节点立即访问。ElasticSearch是基于 Lucene 的搜索服务器,并且提供了标准的 RESTful web接口,作为 Apache 许可条款下的开放源码发布。