hexagonal architecture project structure

Hexagonal architecture was proposed by Alistair Cockburn in 2005. Apply Configurable Dependency Pattern on driven side: Instantiate the hexagon class, which knows of driven ports, and implements a driver port interface. Hexagonal Architecture is an architectural style that moves a programmer’s focus from conceptual layers to a distinction between the software’s inside and outside parts. The main feature of “Hexagonal Architecture”, as opposed to the common layered architecture style, is that the dependencies between our components point “inward”, towards our domain objects: The hexagon is just a fancy way to describe the core of the application that is made up of domain objects, use cases that operate on them, and input and output ports that provide an interface to the outside world. Simon is an independent consultant specializing in software architecture, and the author of Software Architecture for Developers (a developer-friendly guide to software architecture, technical leadership and the balance with agility). The UserAdmin class has no idea how the _userRepo does its thing. I start by recalling EBI and Ports & Adaptersarchitectures. Here’s where our adapter comes in. For example, the instruction “Tell Johnny to meet me at the bank” is an abstraction. A port can represent things like the user, another app, a message bus, or a database. The layer between the core and the outer hexagon is the adapter layer. The business logic (hexagon source code) organization fall out of the scope of Hexagonal Architecture pattern. The latter name, Clean Architecture, is used as the name for this architecture in … The bottom line is that you don’t need to rely on external factors to test your application. Photo by Ilnur Kalimullin on Unsplash … Came up when I searched for ‘hexagon’. How would you suggest to implement it? This is quite different from the typical approach to mocking, which tends to multiply test-specific mocks… and bring us in mock hell. The other packages are hidden to the outside world. I’ve put all the modules in just one GitHub repository, so that you can see and build them all together, but Java 9 allows you to have them in different repositories, compile them apart, and then provide their locations at runtime to choose them dynamically. The adapter might even keep the message in memory. The main theory behind it is decoupling the application logic from the inputs and outputs. The whole project is structured in modules. In the example above, the module host would inject the IUserRepo into the UserAdmin class. Alistair had his “eureka moment” about ports and adapters after reading Object Design: Roles, Responsibilities, and Collaborations by Rebecca Wirfs-Brock and Alan McKean. is an adapter for an actor that interacts with port using a web UI. Exporting a package would be like “publishing” its public types to the outside world. (*) bluezone-parent is a maven configuration module, nothing to do with a Java 9 source code module. The hexagonal architecture is based on three principles and techniques: Explicitly separate User-Side, Business Logic, and Server-Side. A usual way of structuring the hexagon is to split it into two layers: application and domain, following DDD (Domain Driven Design) rules, but this has nothing to do with Hexagonal Architecture. Maven modules) to physically separate the different elements of the architecture. The example application is called BlueZone, and it is described and designed in Chapter 1. But the "hexagonal architecture" name stuck, and that's the name many people know it by today. In doing so, you isolate the central logic (the core) of your application from outside concerns. This is also known as Ports and Adapters architecture. Each adapts the message to the underlying I/O. “Hexagonal architecture” was actually the working name for the “ports and adapters pattern,” which is the term Alistair settled on in the end. I see the modular approach more flexible, since we can add adapters dynamically, without having to recompile the other adapters in the layer. Great article. He writes about topics relevant to technology and business, occasionally gives talks on the same topics, and is a family man who enjoys playing soccer and board games with his children. May 1, 2017 - Explore pat k's board "Hexagonal architecture" on Pinterest. I’d add that another advantages Hexagonal Architecture for testing is that we can reuse almost all the in-memory fakes for all the tests. Test doubles receive output from the application. Phil Vuollet uses software to automate process to improve efficiency and repeatability. The pattern just says that the hexagon offers “ports” to the outside world, for allowing external actors to interact with the hexagon. All our UserAdmin object knows about is the Save method on whatever the _userRepo references via the interface. An adapter doesn’t know of the others, it just depends on the hexagon, and on the actor whose technology it is adapting (for example a database). Alistair had his “eureka moment” about ports and adapters after reading Object Design: Roles, Responsibilities, and Collaborationsby Rebecca Wirfs-Brock and Alan McKean. Here’s a concrete example using some C# code. One of the reasons for creating this pattern was mainly to delegate the infrastructure and UI part of the project, focus on the business rule and make it functional, in addition to not mixing it up, that is, a business rule in the database or even in the UI part of a project. The domain logic is specified in a business core, which we'll call the inside part, the rest being outside parts.Access to domain logic from the outside is available through portsand adapters. We will see this later on, at the end of this article series, as an advanced way of execution. So you should have a package for each adapter, and make types in each package not accessible from others, i.e. Now we need to pass this FakeUserRepo adapter to the UserAdmin in our test code like this: You can see that this test code is passing the FakeUserRepo into the UserAdmin class using its constructor. During my researching on hexagonal architecture, I’ve studied several techniques for implementing the application startup, and I will show them in detail along the next articles in these series. Alistair Cockburn uses to name the hexagon as the “App” … The main purpose of architecture is to improve maintainability and reduce how much time one will have to spend maintaining and modifying their code in the long run. This architecture principle was created by [1] Alistair Cockburn in 2005. The name of a package for a port will be: This way ports are grouped by their side (driver/driven), so that we see at a first glance whether the port is driver or driven. Here’s my own interpretation of a hexagonal architecture diagram: The model is balanced (Alistair has proclaimed his affinity for symmetry) with some external services on the left and others on the right. Notice that it implements IUserRepo. Thirteen years after Alistair’s idea, we commonly use the term “interface” without remembering how the world was without one. In C#, they’re interfaces. But you can structure this source code however you want to, it is not a Hexagonal Architecture issue. This architecture has gone by many names over the years. which has 5 packages for its ports (2 driver and 3 driven): Ports are named following the forDoingSomething pattern, saying what they are for, in a technology agnostic way from the application point of view, i.e. Hexagonal Architecture is a type of architecture that is based on the principle of Ports and Adapters. We don’t need to, since that’s something that comes with the port. Remember that hexagonal architecture is a model for how to structure certain aspects of the application. Alistair explains that the authors “call [the ada… Alistair stressed the importance of decoupling the application from the UI. Hexagonal architecture is a model ofdesigning software applications around domain logicto isolate it from external factors. But first, let’s talk about why this is desirable. Improve your .NET code quality with NDepend. Having inputs and outputs at the edge means you can swap out their handlers without changing the core code. The packages it “publishes” (exports) to other modules. https://web.archive.org/web/20180822100852/http://alistair.cockburn.us/Hexagonal+architecture, https://jmgarridopaz.github.io/content/hexagonalarchitecture.html, https://www.youtube.com/watch?v=th4AgBcrEHA&list=PLGl1Jc8ErU1w27y8-7Gdcloy1tHO7NriL, https://web.archive.org/web/20170624023207/http://alistair.cockburn.us/Configurable+Dependency, https://tpierrain.blogspot.com/2016/04/hexagonal-layers.html, https://github.com/tpierrain/hexagonalThis/blob/master/Hexagonal.pdf, io.github.jmgarridopaz.bluezone.hexagon.driver.forparkingcars, io.github.jmgarridopaz.bluezone.hexagon.driver.forcheckingcars, io.github.jmgarridopaz.bluezone.hexagon.driven.forobtainingrates, io.github.jmgarridopaz.bluezone.hexagon.driven.forstoringpermits, io.github.jmgarridopaz.bluezone.hexagon.driven.forpaying, // Implement the driver port operation calling driven ports operations, io.github.jmgarridopaz.bluezone.startup.forparkingcars.test, io.github.jmgarridopaz.bluezone.startup.forparkingcars.webui, io.github.jmgarridopaz.bluezone.startup.forcheckingcars.test, io.github.jmgarridopaz.bluezone.startup.forcheckingcars.cli, /* newcomer to F# might be tempted to organize code in classes just like in C# By modules I mean source code subprojects (e.g. The part could be as specific and long as you want. ). But it got me thinking on how to implement transactions. The host could be a web app, a console application, a test framework, or even another app. Hexagonal architecture was proposed by Alistair Cockburn in 2005. But we would have to change this file and recompile the hexagon, every time we add a new adapter. You can swap in fakes for testing, which makes the tests more stable. Hexagonal Architecture ,also known as Ports and Adapter pattern is an architectural style which promotes and gives structure for achieving separation between actual application / domain logic and various technology concerns and external actors.Alistair Cockburn has a detailed articleon this architecture style and below is short definition from the same article. This architecture pattern says nothing about the structure inside the hexagon, it can be whatever you want. This arhictecture also goes under the names ports and adapters (which better explains the central idea behind it) and onion architecture … Applying Hexagonal Architecture: main principles. Module A is the UserAdmin class. This is the biggest benefit of hexagonal architecture! That’s where you’d adapt the action and message to the appropriate application class—in this case, UserAdmin. The pattern definition doesn’t say anything about how to implement the architecture. For other modules to see the public type, you have to export the package the type belongs to. The hexagonal architecture, or ports and adapters architecture, is an architectural pattern used in software design. This implies that you can have several type of automated testing from unit testing using mocks to functional e2e tests using scoped transactions or in-memory DBs to the production environment. Download the NDepend Trial and understand your .NET code base technical-debt within a few minutes. Alistair Cockburn changed the terminology from “hexagonal architecture” to “ports and adapters.” Thankfully, hexagonal architecture sort of stuck. This is important, since driver ports operations are called by an adapter, while driven port operations are implemented by an adapter. It has no way of knowing who or what will actually receive the message. In hexagonal architecture terms, the interface is the port. This module configures the dependencies between the hexagon and the adapters, applying the Configurable Dependency Pattern at both driven and driver side, following these steps: Here is a hand-drawn diagram I made once about this topic: Figure 3: Dependency Configurator in Startup Module, I offered this picture to Alistair Cockburn, who published it on Twitter: The analogy kind of falls apart there. Whether an adapter plays different roles: it drives more than one port; or it is driven by more than one port; or it is driven by a hexagon port and it drives a port of another hexagon… it’s up to you, but then you should know that you are not following the SRP (Single Responsability Principle). It just sounds a heck of a lot cooler! We could be more specific and say more about the technology. This way, we can change the underlying technologies without having to modify the application core. Hexagonal Architecture, a layered architecture, is also called the Ports and Adapters architecture. The port of the hexagon is either driver or driven, and so will be the adapter. The sides are simply representations in the model for ports. Hexagonal architecture is a model or pattern for designing software applications. Module A sends a message to module B via the IUserRepo interface. Hexagonal architecture was proposed by Alistair Cockburn in 2005. The goal is to make the application easier to test. It publishes (exports) the packages with the ports. For each driven port, instantiates a driven adapter, which implements the driven port interface. My vision of Hexagonal Architecture is modular, with the hexagon at the center, and adapters around it, belonging to no layer, each one attached to a port of the hexagon. It’s important to note the use of the term “Interfacers” in that wiki entry because that’s really what it’s all about! Dependencies are going from User-Side and Server-Side to the Business Logic. This is the power of the adapter! Let’s look at that UserRepo again in light of testing. Apply Configurable Dependency Pattern on driver side: Instantiate a driver adapter, which knows of the driver port of the hexagon. https://twitter.com/TotherAlistair/status/1122918489558278145. Hexagonal Architecture (aka Ports and Adapters) is one strategy to decouple the use cases from the external details. In the example application, the name of the hexagon module is. To give you a common scenario of how this works in practice, let’s say we’re using a .NET testing framework such as xUnit. We isolate the boundaries by using Ports and Adapters. The point is to make the core independent of its inputs and outputs. This makes components exchangeable at any level and facilitates test automation. The inside part is use cases and the domain model it’s built upon. Hexagonal architecture is all about swapping components—specifically, external components. Abstraction just means we don’t know how something does what it does. This architecture follows the premise of guaranteeing the total abstraction of the domain with respect to all the dependencies we may have (repositories, frameworks, third-party libraries, etc. So it is not layered “per se”, it is not component-based (modular) “per se”, etc. This is where he really sought to differentiate his approach from layered architecture. Personally I prefer the term Ports and Adapter as it clearly tells what this style is … At either driver or driven side, the Configurable Dependency Pattern applies as follows, quoting Alistair Cockburn in his “Alistair in the Hexagone” talk: The one who does the triggering has to know the dependency. Basically, you can put whatever you need on the other side of the port! It’s specifically about dealing with I/O. But what does that look like, you ask? For example, a driver adapter is a generic class with one type parameter, which is the driver port interface that it uses. Figure 2: Ports packages in hexagon module. In Java 9, a module is a set of packages, that you can compile apart generating a jar file. The hexagonal architecture was invented by Alistair Cockburn in an attempt to avoid known structural pitfalls in object-oriented software design, such as undesired dependencies between layers and contamination of user interface code with business logic, and published in 2005. In our example application, we are going to develop 2 adapters for each port: The root package for the source code of an adapter would be: This module is the entry point to the application. Notice how the UserAdmin only knows about the interface. A driver adapter will be a Java class that “uses” a driver port interface, and a driven adapter will be a class that “implements” a driven port interface. no matter the technology of the actor that is behind the port. This is because it has the concept of different ports, which can be adapted for any given layer. With an abstraction, we only know the high-level details. This way, your test framework will drive the application through those ports. Now let’s see the modules and the convention I follow for naming them and their packages. Measure quality with metrics, generate diagrams and enforce decisions with code rules, right in Visual Studio. The business core interacts with other components through ports and adapters. Usually, I’d put that on my service, but doing so I’d be putting a infrastructure detail inside of my business. So we will have a package for each port of the hexagon. The different adapters depending on a port stand for different swappable technologies that the actor communicating with the hexagon might use. A FakeUserRepo might look like this: This is a fake because it stores the data in memory in the List. */, “Java 9 Modularity: Patterns and practices for developing maintainable applications”, by Sander Mak & Paul Bakker, https://twitter.com/TotherAlistair/status/1122918489558278145, quoting Alistair Cockburn in his “Alistair in the Hexagone” talk. It will be a set of Java classes, types, etc implementing the operations defined at driver port interfaces, and calling operations on driven port interfaces. The important thing with this way of naming modules, is that when we see a module name at first glance, we know whether it is business logic or it deals with real world technology, since the first word after the application name is either “hexagon” or “adapter”.