Example of EntityFramework

EntityFrameworkExample.cs

using System;

/*
	
	THIS FILE WORKS BEST WHEN READ FROM TOP TO BOTTOM


	WARNING, ENTITY FRAMEWOKR IS REALLY COOL BUT IM NOT AN EXPERT.


	There are 3 ways of declaring stuff in entity framework.
	But the one I used mainly is code-first, which is where you 
	make your code and the database is generated in order to support the model the code presents.
	https://msdn.microsoft.com/en-us/data/jj193542.aspx

*/



/*
	
	First, off we need a class that represents the data of a single user.
	And make a class out of it



*/
public class SkyhookViewer
{
	//Based on HotBot.Plugins.Wallet.WalletValue

	//System.ComponentModel.DataAnnotations.KeyAttribute
	//Indicates this field is the primary key
	//from what I've seen this must be a Guid or an int type.
	[Key]
	public Guid Id { get; set; }

	//System.ComponentModel.DataAnnotations.Schema
	//Also, we want to make sure that all usernames are unique
	//so this will prevent double entries for any single viewer.
	[Index(IsUnique = true)]
	[StringLength(Verify.MaximumUsernameLength, MinimumLength = Verify.MinimumUsernameLength)]
	public string Username { get; set; }

	//Quick thing to store money as a simple example.
	//C# 6.0 notation, same effect when setting this in the PARAMETERLESS (a.k.a. default) constructor.
	//Entity framework will set this value after the constructor is run if it is created from a database constext
	public double Money { get; set; } = 0;
}
/*

	Now to create the connection with the database, simply create a class that is derived from DbContext
*/
public class SkyhookContext : DbContext
{
	//Based on HotBot.Plugins.Wallet.WalletContext

	//The DbSet will automatically create a list-like structure that you can store instances on and query.
	public DbSet<SkyhookViewer> Viewers { get; set; }

	//Now here's the cool part, when you use LINQ on the DbSet.
	//it translates it into SQL and executes it directly on the database!!!!!
	//No more manual querries, the entity framework allows you to use adapters
	//(based on app.conf) and the adapter is responsible for creating the query.
	//There already are adapters for the most common database engines.
	//Check my hotbot project to see how I used configs to setup for local db storage.

	public SkyhookContext()
	{
	}

}

//Personally I like to split off the logic from the context because of the using-context pattern (see below)
public class UserManager
{
	//Based on HotBot.Plugins.Wallet.WalletPlugin

	public double GetMoney(string username)
	{
		using (var context = new SkyhookContext())
		{
			//The using statement guarantees that context.Dispose() is called whenever the code leaves the using block
			var viewer = context.Viewers.FirstOrDefault(v => v.Username == username);
			if (viewer != null)
			{
				return viewer.Money;
			}
			else
			{
				return 0d;
			}
		}
	}
	public void SetMoney(string username, double value)
	{
		using (var context = new SkyhookContext())
		{
			SkyhookViewer viewer = context.Viewers.FirstOrDefault(v => v.Username == username);
			if (viewer == null)
			{
				viewer = new SkyhookViewer();//Just create a instance and add it to the context's list
				context.Viewers.Add(viewer);
				viewer.Username = username;
				viewer.Money = value;
			}
			viewer.Money = value;
			context.SaveChanges();//Executes the update/insert query.
		}
	}
}