Entity Framework - What is Null?

CSharp · Console

/Program.cs

using System;
using System.Collections.Generic;
using System.Linq;

public class user_mstr
{
	public string user_cd;
}

public class FakeContext
{
	public List<user_mstr> user_mstr;
}

public class Program
{
	private static string strUserCD = "foo";
	
	private static void FirstUserAsNull()
	{
		try
		{
			Console.WriteLine("OneUserAsNull");
			FakeContext ctx = new FakeContext();
			ctx.user_mstr = new List<user_mstr>() { null, new user_mstr(), new user_mstr() };
			user_mstr vwUser = ctx.user_mstr.FirstOrDefault(x => x.user_cd == strUserCD);
		}
		catch (NullReferenceException e)
		{
			Console.WriteLine(e.Message);
		}
		catch (ArgumentNullException e)
		{
			Console.WriteLine(e.Message);
			Console.WriteLine();
		}
	}
	
	private static void UserListAsNull()
	{
		try
		{
			Console.WriteLine("UserListAsNull");
			FakeContext ctx = new FakeContext();
			ctx.user_mstr = null;
			user_mstr vwUser = ctx.user_mstr.FirstOrDefault(x => x.user_cd == strUserCD);
		}
		catch (NullReferenceException e)
		{
			Console.WriteLine(e.Message);
		}
		catch (ArgumentNullException e)
		{
			Console.WriteLine(e.Message);
			Console.WriteLine();
		}
	}

	private static void CtxAsNull()
	{
		try
		{
			Console.WriteLine("CtxAsNull");
			FakeContext ctx = null;
			user_mstr vwUser = ctx.user_mstr.FirstOrDefault(x => x.user_cd == strUserCD);
		}
		catch (NullReferenceException e)
		{
			Console.WriteLine(e.Message);
			Console.WriteLine();
		}
	}

	public static void Main()
	{
		CtxAsNull();
		UserListAsNull();
		FirstUserAsNull();
	}
}