Vidyasagar MSC

Onion Architecture : ASP.NET

Cutting Layers without Crying

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ABOUT ME• Coder by Profession | Gamer by Heart |

Polyglot & Pragmatic Programmer

• Microsoft MVP – Xbox | Intel Software Innovator | Developer @ DELL

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• http://about.me/mscvidyasagar

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What’s software architecture?

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Architectural Style

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Layered Architecture

Partitions the concerns of the application into stacked groups (layers).

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Traditional 3-layer Architecture

Infrastructure / DAL

Core / BLL

UI

DB

Uti

liti

es

/ C

om

mon

/ S

hare

d

nHibernate /

LINQ to SQL

ASP.NET

Log4Net

AutoMapper

StructureMap

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• Very easy for developers over time to put more and more business logic in the UI layer

• Counter-productive to build your application on top of a specific technology that is sure to change over time

• Logic is easily scattered all over, locating code becomes a major effort.• Developers over time struggle to determine where code should go… DAL? BLL?

Utilities?• Business logic has many tentacles extending from it (directly and indirectly)• Library explosion: Makes it easy take a dependency without putting much thought

into it, and now it’s littered all over the code base

Problems with Traditional Architecture

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The Onion Architecture to rescue• Quoted by Jeffrey Palermo in 2008.• relies heavily on the Dependency Inversion principle.• The database is not the center.  It is external.

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Dep

en

den

cy

Reso

luti

on

User I

nterface

Infrastructure

ProductRepository<<class>>

Application Core

Application Services

Domain Services

Domain Model

IProductRepository

DB

IUserSession

HttpUserSession<<class>>

ProductsControllerBrowser hits: /Products/List

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• Everything unique to the business: Domain model, validation rules, business workflows

• Defines all technical implementation (non-business) needs as interfaces

• CANNOT reference any external libraries• NO technology specific code

Core

• Provide implementations for Core interfaces• Call web services, access a database• CAN reference external libraries to provide implementations• ONLY technology specific code (non-business) belongs in

infrastructure

Infrastructure

• Very thin layer, has no logic of its own• Wires up Core interfaces to Infrastructure implementations. • Runs startup/configuration logic

Dependency Resolution

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