Building a Server App With SOA and WebAPI

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Building Server Applications with SOA

and WebAPI

Doncho Minkov

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Application Layers Data Layer

Repositories Layer

Services Layer

The repository pattern Creating repositories to unify

database interactions

Inversion of Control and dependency Injection Using DependencyResolver
































The Repository Pattern































free C# book, безплатна книга C#, книга Java, книга C#Дончо Минков - сайт за програмиранеНиколай Костов - блог за програмиранеC# курс, програмиране, безплатно The Repository Pattern

The repository pattern wraps the access to data stores (like databases, XML, services…) Exposes only interfaces to interact

with a data store

Used for higher code-reusability and testability

The app's business layer contains a single instance of a repository Used to perform CRUD operations

over the data store
































The Repository Pattern: Example

public interface IRepository<T>{ T Add(T item); IEnumerable<T> GetAll(); …}

public interface IPlacesRepository : IRepository<PlaceDto>{ }

public class DbPlacesRepository: IPlacesRepository{ public PlaceDto Add(PlaceDto Add){ … } public IEnumerable<PlaceDto> GetAll(){ … } }
































The Repository Pattern

Live Demo
































Why These Repositories?

Repository pattern has the f0llowing features: Testability of the application

When the testing of the repositories is done, they can be mocked to test the business layer

Reusability or the repositories When creating a new business layer

working with the same Database (like admin panel)

Extensibility of the business layer In need of more repositories, they

can be easily produced
































Repository Pattern in WebAPI

































To use the repository pattern in WebAPI just create an instance of the IRepository<T> interface inside the controller And use the repository to interact

with the DBpublic class PlacesController : ApiController{ private IPlacesRepository repository; public PlacesController() { this.repository = new DbPlacesRepository(); } public IEnumerable<PlaceDto> GetAll() { return this.repository.GetAll(); }}
































Repository Pattern in WebAPI (2)

Yet in the example the controller instantiates the repository The controller is tightly coupled

with the DbPlacesRepository class

This can be fixed using Inversion of Control and Dependency Injection

































Live Demo
































Inversion of Control (IoC)

































Inversion of Control is a way to loosen the coupling between components Makes testing easier

Makes extensibility easier

IoC is a technique that allows coupling of objects at run time, instead of compile time IoC gives objects the dependencies

they need

If the controller expects an instance of the IRepository<PlaceDto> interface, the IoC gives it a suitable instance































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There are many ways to implement IoC: Factory design pattern

Service locator pattern

Dependency injection

Template method design pattern

Strategy design pattern

Etc…

WebAPI has built-in dependency injection for controllers































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Dependency injection removes the hard-coded dependencies between objects and allows changing them run time

The primary idea behind DI is selection of single implementation of interface between many present Decide run time which of the many

implementations of IRepository<PlaceDto> to use for the controller
































Dependency Injection in WebAPI

WebAPI has by default a dependency injector for controllers, called DependencyResolver Instantiates controllers with their

default constructor

Yet this can be changed to instantiate another constructor

Each WebAPI application has a DependecyResolver, deciding how to initialize controllers































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The dependency resolver of a WebAPI app can be changed with a custom implementation Create a class that inherits from IDependencyResolver and implement its GetService() method:public class DbDependencyResolver: IDependencyResolver

{ static IRepository<Place> placesRep = new DbPlacesRepository(); public object GetService(Type serviceType) { if (serviceType == typeof(PlacesController)) return new PlacesController(placesRepository); else return null; } …}

































Live Demo
































Application Layers































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A server application is build from three layers A data layer contains

Access to the data source (database, XML, etc…)

EntityFramework DbContext, XDocument, etc…

A repositories layer contains Repositories with CRUD operations over

a DB

A service layer contains A reference to a repositories layer

A reference to the data layer

Controllers with actions for a REST API































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The Data Source

Data Layer Repositories

Services Layer(Business layer)

MS SQL, MySQL, XML, Web services

Entity Framework, OpenAccess, Linq-to-XML

WebAPI controllers
































The Places DatabaseCreating a Sample Application































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Develop an application to store places of interest Each place has coordinates, name, a

set of categories and optional description

Every user can leave a comment or vote for a place The user needs to type in their

username

No user authentication required

Categories have a name and set of places
































The Database































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Create a database for the application i.e. using MS SQL Server

Create tables, relations, schema, etc…

Create store procedures and indexes

Create everything needed for an app database
































Creating The Database

Live Demo
































The Data Layer































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The data layer contains a way to connect to the database Entity Framework

Database-first or Code-first

ADO.NET

LINQ-to-SQL

LINQ-to-XML

Etc…
































Creating the Data LayerLive Demo
































The Repositories Layer































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The repository layer exposes repositories to work with the Database Using the Repository Pattern

The repositories introduce methods to perform CRUD operations over the data store In our case over the Places

database
































Creating the Repositories

LayerLive Demo
































The Services Layer































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The Services layer is the layer that contains the business logic It uses the repositories for data

interactions Yet has no direct dependency over

the data store

The Services layer contains all the controllers that are used by the Service Consumer Handles computing and error

handling































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The Services Layer is the place where ASP.NET WebAPI steps in It is the only layer that is

dependent to the WebAPI framework

The Services layers uses the repositories to interact with the Data store and WebAPI to communicate with the Consumers Each controller has a repository

instance for data store interactions The repository instances are received

by IoC
































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Questions?

Building Server Apps with WebAPI







































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Building a Server App With SOA and WebAPI