How to use SQLite in ASP.NET 5

Standard

SQLite is a software library that implements a self-contained, serverless, zero-configuration, transactional SQL database engine. SQLite is the most widely deployed SQL database engine in the world. Most of the ASP.NET 5 tutorials / articles, SQL Server is used. In this post I am explaining about how to use SQLite with Entity Framework 7.0.

First you need to modify the project.json file, and need to add SQLite and Entity Framework dependencies. (“EntityFramework.SQLite”: “7.0.0-*”),the project.json, dependencies section will look like this.

{
    "dependencies": {
        "Microsoft.AspNet.Diagnostics": "1.0.0-beta1",
        "Microsoft.AspNet.Hosting": "1.0.0-beta1",
        "Microsoft.AspNet.Mvc": "6.0.0-beta1",
        "Microsoft.AspNet.Server.WebListener": "1.0.0-beta1",
	"Microsoft.AspNet.Identity.EntityFramework": "3.0.0-*",
	"EntityFramework.SQLite": "7.0.0-*"
    }
} 

Now you need to create DbContext class. If you are using SQL Server, you can generate it using scaffolding(For SQLite, it did worked for me.) Here is minimal DbContext class and the model class I have created.

using System;
using Microsoft.Data.Entity;
using Microsoft.Data.Entity.Metadata;

public class Message
{
	public Guid Id { get; set; }
	public string Content { get; set; }
	public DateTime CreatedOn { get; set; }
	public string CreatedBy { get; set; }
}

public class HelloWorldContext : DbContext
{
	public DbSet<Message> Messages { get; set; }
	protected override void OnConfiguring(DbContextOptions builder)
	{
		builder.UseSQLite("Filename=messagedb.sqlite;");
	}

	protected override void OnModelCreating(ModelBuilder builder)
	{
		builder.Entity<Message>().Key(m => m.Id);
		base.OnModelCreating(builder);
	}
}

As you are using EF code first (creating the DB on the fly), you need to add the following code in the constructor of the Startup.cs, which will ensure SQLite Db is created, it is similar to Database Initializer classes in Entity Framework.

using(var context = new HelloWorldContext())
{
	context.Database.EnsureCreated();
}

This method won’t throw exception even if DB exists. Now you can write simple EF insert statement to insert data to the Table.

var helloWorldContext = new HelloWorldContext();
helloWorldContext.Messages.Add(new Message() {
	Id = Guid.NewGuid(),
	Content = "Hello World",
	CreatedOn = DateTime.Now,
	CreatedBy = "Anuraj" });
helloWorldContext.SaveChanges();

In the next post I will try explain how to scaffold controllers and views in ASP.NET 5 with SQLite.

Happy Programming :)

Expression Bodied Functions and Properties in C# 6.0

Standard

Expression bodied functions are another syntax simplification in C# 6.0. These are functions with no statement body. Instead, you implement them with an expression, similar to Lamda expressions.

class Calculator
{
    public int Add(int a, int b) => a + b;
    public int Subtract(int a, int b) => a - b;
}

As with most of the features found in C# 6.0, they’re intended to provide a simplified syntax for cases where the implementation is simple. The return type of the expression should match the return type identified in the function declaration. Void methods, don’t return anything. The expression bodied simplification also available for properties (getter only).

Verify Internet connection is available using C#

Standard

While reviewing some code, I found a snippet for checking internet connection, like this

private static bool IsConnectedtoInternet()
{
	bool IsConnectedtoInternet;
	try
	{
		using (WebClient client = new WebClient())
		{
			using (client.OpenRead("http://www.microsoft.com"))
			{
				IsConnectedtoInternet = true;
			}
		}
	}
	catch
	{
		IsConnectedtoInternet = false;
	}
	return IsConnectedtoInternet;
}

I found this way of internet connection availablilty many times, but most of the times it was google.com :) So I thought of writing the correct way (at least from my prespective) of verifying internet connection. For this I am using a WIN32 API, InternetGetConnectedState method, from wininet.dll. And here is the snippet.

[DllImport("wininet.dll")]
private extern static bool InternetGetConnectedState
    (out int Description, int ReservedValue);
private static bool IsConnectedtoInternet()
{
    int description;
    return InternetGetConnectedState(out description, 0);
}

Happy Programming :)

Dependency Injection in ASP.NET 5

Standard

Dependency injection is a software design pattern that implements inversion of control and allows a program design to follow the dependency inversion principle. An injection is the passing of a dependency (a service) to a dependent object (a client). The service is made part of the client’s state. Passing the service to the client, rather than allowing a client to build or find the service, is the fundamental requirement of the pattern. The pattern is used to create program designs that are loosely coupled and testable.

Types of Dependency Injection

  • Constructor injection: the dependencies are provided through a class constructor. – ASP.NET 5 supports only this.
  • Setter injection: the client exposes a setter method that the injector uses to inject the dependency.
  • Interface injection: the dependency provides an injector method that will inject the dependency into any client passed to it. Clients must implement an interface that exposes a setter method that accepts the dependency.

In ASP.NET 5, dependency injection is a first class citizen. While in the previous versions of the framework, DI was partially supported, in ASP.NET 5 it is available throughout the entire stack. A minimalistic DI container is provided out of the box, but you can use your own container (BYOC – Bring Your Own Container support).

The default dependency injection supports following life styles.

Lifestyle Description
Instance A specific instance is given all the time. You are responsible for its initial creation
Transient A new instance is created every time
Singleton A single instance is created and it acts like a singleton
Scoped A single instance is created inside the current scope. It is equivalent to Singleton in the current scope

A popular feature for DI in web applications is to create objects that have a single instance per web request. This means that the objects acts as a singleton inside that request but two distinct requests will have different instances of the objects.

In this post, I am injecting database repository to the controller with scoped life style – runtime will create instance of repository on every web request. Here is the changes required in the Startup.cs.

public void Configure(IApplicationBuilder app)
{
	app.UseErrorPage();
	app.UseServices(services =>
	{
		services.AddMvc();
		services.AddScoped<IUserRepository, UserRepository>();
	});

	app.UseMvc();
}

And in the controller, create a constructor, which accepts IUserRepository parameter, which will be injected by runtime while creating the instance of contolller.

public class HomeController : Controller
{
	private IUserRepository _userRepository;
	public HomeController(IUserRepository userRepository)
	{
		_userRepository = userRepository;
	}
	
	public ActionResult Index()
	{
		return View(_userRepository.Users()); 
	}
}

Here is the IUserRepository interface and its implementation.

public interface IUserRepository
{
	List<User> Users();
}
	
public class UserRepository : IUserRepository
{
	public List<User> Users()
	{
		var listOfUsers = new List<User>();
		for(int i = 0; i< 10; i++)
		{
			listOfUsers.Add(new User(){ Name = "User " + i });
		}
		
		return listOfUsers;
	}
}

public class User
{
	public string Name { get;set; } 
}

You can find more details about Dependency Injection in ASP.NET vNext here

Happy Programming :)