NET 4.0下的N层领域驱动架构指南

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"N-Layered Domain-Oriented Architecture Guide with .NET 4.0" 本文档是一份关于使用.NET Framework 4.0进行N层领域驱动设计（DDD）架构的指南，由多位微软员工、技术贡献者以及行业专家共同编撰。N层架构是一种常见的软件设计模式，它将应用程序分解为多个独立的、有明确职责的层，以提高可维护性、可扩展性和可重用性。一、引言 N层架构的核心理念是通过分层来组织系统，每个层专注于特定的功能或职责。在.NET 4.0环境下，这通常包括用户界面层（UI）、业务逻辑层（Business Logic Layer, BLL）、数据访问层（Data Access Layer, DAL）和服务层等。这样的设计有助于保持代码的清晰性和模块化，同时降低了不同组件之间的耦合度。二、领域驱动设计（DDD） DDD是一种软件开发方法，强调以业务领域为中心，通过建模来理解复杂业务问题。在N层架构中，领域层（Domain Layer）是核心，包含了业务规则和实体对象。领域模型应尽可能反映业务专家的语言和概念，确保软件能够准确地处理业务逻辑。三、用户界面层用户界面层负责与用户交互，通常包括Web应用、桌面应用或移动应用。在.NET 4.0中，可以使用ASP.NET MVC、WPF或WinForms等技术实现。这一层应当尽量轻量，不包含任何业务逻辑，仅负责展示数据和接收用户输入。四、业务逻辑层业务逻辑层是应用程序的核心，包含了所有的业务规则和流程。这些规则不应该在UI层或DAL层中处理，而应该在BLL中集中管理。.NET 4.0提供了强类型和面向对象的特性，使得编写和维护业务逻辑更加方便。五、数据访问层数据访问层负责与数据库的交互，包括数据的读取、写入和更新。在.NET 4.0中，可以使用Entity Framework、NHibernate或其他ORM工具简化数据库操作。DAL应提供一个抽象接口，使得上层可以无感知具体的数据存储技术。六、服务层服务层（Service Layer）用于协调各层之间的通信，它可以是WCF服务、Web API或其他形式的服务。服务层可以提供跨层的业务操作，如事务管理、安全验证和远程调用等。七、其他考虑 - 隔离：各层之间应通过接口进行通信，而不是直接引用，以增强解耦。 - 测试：采用单元测试和集成测试确保代码质量，TDD（测试驱动开发）和BDD（行为驱动开发）是推荐的实践。 - 持续集成和部署：利用自动化工具进行构建、测试和部署，以提高效率和一致性。总结，N-Layered Domain-Oriented Architecture Guide with .NET 4.0提供了详细的指导，帮助开发者在.NET 4.0环境中构建健壮、可扩展的多层应用程序，强调了领域驱动设计的重要性，并给出了具体的实现策略和技术选择。这份指南对于理解和实践企业级软件开发具有很高的价值。

Prologues xv

Prologue by Aurelio Porras

(Developer Solution Specialist, Microsoft DPE)

I had the opportunity to participate in the development of some applications of a certain

relevance and I happily remember these meetings at the beginning of projects where

we drafted with boxes and arrows the architecture skeleton, we detected patterns and

labeled any element of the diagram with the latest technologies available that helped us

implement in the best possible way the required functionality without having to

reinvent the wheel. In these architecture discussions, the typical quarrels appeared

about the level of complexity of the application architecture to be implemented; on one

hand, the ones in favor of mounting a simpler architecture using code libraries and

implementations of patterns already built, to produce business logics immediately and

to present results as soon as possible, giving more freedom to the developer when using

technologies; and on the other hand, the ones in favor of building a more complex

architecture, building libraries and implementing patterns in accordance with the

application to speed up the production of business logics after that, although the results

appeared later, increasing the level of abstraction to prevent the developer from having

to make technological decisions. It was interesting to see how the “simplistic group”

rebuked the “complex group” the wasted effort in building unnecessary church arcs

that the technological infrastructure manufacturers in the following version would

make obsolete and tedium of the developer of business logics that sometimes stopped

being a programmer and turned into a mere person in charge of setting up the

architecture; and the “complex group” scolded the “simplistic group” for the amount of

duplicated code they threw away to the garbage and the effort in coordination they

wasted to avoid those functional duplicity problems by giving so much freedom to the

developer. Yes, it sounds like grandpa‟s stories that are told over and over, but these

were very amusing meetings.

The final result of these discussions was a series of architecture decisions

determining the technological infrastructure to be used to build the application, the

relationships with external systems, the organization of the code in layers, the libraries

already available for use, and the ones to be developed customized, among other

things. I remember in particular how we tried to de-couple parts of the application to

enable its future evolution, up to the limit allowed by the state of the art technology at

that time, to be able to modify or extend the business logics not having to touch all the

modules or to be able to interchange one of the external systems, the applications

server or the database with no problem.

But these architecture decisions were not only conditioned by technical factors such

as technological infrastructures, programming language or development tools; but also

by factors related to development of a software project such as budget and duration,

milestones and deliverables, experience of the development team, business knowledge

and all the things the projects have. At the end, architecture could suffer the unwanted

cuts due to “project decisions”.

So, unfortunately, I also had the chance to verify how certain architecture decisions

can condemn the future of great applications. I know the case of a financial application

that could adapt to business changes very quickly, thanks to the high level of

xvi N-Layered Domain-Oriented Architecture Guide with .NET 4.0

abstraction its architecture provides; the user himself is capable of modifying the

application logics through a visual tool and programming a pseudo-language of

business; the problem is that capacity of integration in line with other systems is very

limited because it is built on obsolete technologies and its coupling to them is such, that

the cost of migrating to the latest technologies is too high and is not justified from the

business point of view; especially if we consider that the application still works as a

charm and following the rule of our industry, if it works, don‟t touch it. I also know

other financial application that is well de-coupled from the applications server and the

database and it is relatively simple to update it technologically, but it did not take care

of the code organization and the business logics is so intricate in the different

application layers that it is not quickly adapted to changes as it would be good for

business, and streamlining it would involve rewriting most part of the application; this

is unthinkable, almost a new project. Surely, the two applications were created this way

due to the particular circumstances of the corresponding projects, but it is clear that

architecture decisions made at that time negatively affected the evolution maintenance

of those two applications, which, as it was expected from the beginning, would have

long duration in the production environment.

This is the root cause of this guide. Naturally, the state of the art technology has

changed a lot, the architecture trends, the capacities of modern technological

infrastructure, the new things in programming language and new development tools

help a lot to build weakly coupled architectures to enable evolution maintenance of the

applications; but if, also we conceive application architecture considering first the

importance of its future evolution, to adapt easily to the business changes and to add

the latest technologies replacing the oldest ones, we will be close to building a great

business application with healthy life guaranty.

And this is what the guide is about, building an architecture that de-couples the

business logics of the technology used to build the application so that one can evolve

independently from the other. And it does not only talk about birds and flowers, but it

also goes to a level of technical detail that will show us in the latest .NET technologies

and Microsoft development tools and its application in great business applications,

indicating when to use which technology and why, and including also the sample

application code following the precepts set forth throughout the whole guide.

I thank César for all this clarifying material, for his effort leading this initiative that

will surely help architects and developers to approach application architectures with a

more holistic vision, and I also thank the authors and collaborators that participated in

its preparation. Congratulations on the result.

Prologues xvii

Prologue by Israel Garcia Mesa

(Consultant - Microsoft Services)

We currently have a wide range of technological options we can use in our projects and

that cover many needs being detected through the years. The experience we have in

Microsoft Ibérica is that this variety of choices does not resolve all the problems of the

projects in our customers. The analysis we made and we continue to make to be better

every day has given us a series of conclusions we want to share in this guide.

Some thoughts about Architecture

The development of a software construction project is a process where many factors

are involved, and that is why it is important to have the suitable tools. Currently there

are many technological options available that help us compose our solutions, but,

however, they do not mitigate the main problems of a project:

 Needs of adaptation to changes in projects (functional and technical

requirements) that can have great impact on the effort.

 Uncertainty when choosing and using technology that best fits each

scenario.

 Integration with legacy systems that do not have a clear alignment with the

project requirements.

These and other situations can affect the development of projects and increase the

possibility of new risks appearing that impact on the project. To mitigate these risks the

following is recommended:

 The methodology of work must be adapted to our team, type of project and

customer, since this will be our tactic to meet our goal and all the details

must be considered. So it is important to choose a work method adapted to

the context of the project where the type of solution and work team must be

considered.

 Consider an architecture model that meets the known needs and with a low

coupling level, which will enable its adaptability. In this point different

options can be chosen when approaching the system, but following the

model proposed by the Domain Directed Design (DDD) can help us follow

the most suitable approach.

The design of the solution, besides being an incremental process, can be a process

to be performed from different approaches until completion of the solution vision.

From the experience gathered in the different projects we have developed we have

considered useful some approaches we summarize below:

 Solutions, of whatever size, are born from a global design where technical

aspects are not relevant (we could talk about conceptual design) and

subsequently design the parts of the solution as we focus on each one of

xviii N-Layered Domain-Oriented Architecture Guide with .NET 4.0

them. With this model, slowly, we will get closer to the details of

implementation de-coupling the design, reducing complexity and the

possibility that a technical problem can affect the rest of the solution.

 Also, it will be necessary to conjugate the design of the logical model with

the physical model or models, ideally an approach would condition the

other to the least extent possible. This type of approach enables reuse and

adaptability of the solution to the different scenarios.

There will always be a desire to build a solution around the idea that technology

will solve our problems, and we will think this is a shortcut to our goals. However, we

can discover this is not the quickest path since, when a design cannot grow and/or

evolve because it requires a lot of effort or we do not control the impact of such

changes, this is when the technology does not bring value to the solution and can

become a problem.

Additionally, there is a series of very useful tools to build a solution and that help us

to face changes in implementation and its design:

 Test Development: having unit tests and automated functional tests will

help us know the stability of our solution, and therefore determine if any

change could affect the solution and to what extent.

 Refactorization: approaching and implementing changes in a solution

through refactoring techniques is an efficient manner that helps us control

their impact. Complementing refactoring with the use of tests helps

reducing risks, so these are two perfectly complementary tools.

 Communication: a good communication inside the team reduces

possibility of working inefficiently or even duplicating functionality.

Besides it is a useful tool in our relationship with the customer, helping us

place common expectations, detecting new requirements or possible risks,

in quick and agile manner.

These conclusions that can seem logical and, however, so difficult to be carried out, are

the reason why we want to share knowledge of this guide so that our experience can be

useful in projects and so that technology becomes that tool that makes our job easier.

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