entity framework cannot open database - entity-framework

Question

I'm following the EF - Code First example at http://msdn.microsoft.com/en-us/data/jj193542.aspx. This example works fine. The example creates a LocalDB on my harddrive containing the database files .mdf and .ldf.
If I delete these 2 files, I get a Cannot open database exception, if I replace the files, it works. If I change the name of my DbContext and it will work.
Heres my question:
Why do I not get an exception when I first run the example ? Something somewhere appears to remember the filename/context name. What is the correct way to handle this ?
Class and DBContext below, exception throw at db.Blogs.Add(blog);
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Data.Entity;
class Program
{
static void Main(string[] args)
{
using (var db = new BloggingContext())
{
// Create and save a new Blog
Console.Write("Enter a name for a new Blog: ");
var name = Console.ReadLine();
var blog = new Blog { Name = name };
db.Blogs.Add(blog);
db.SaveChanges();
// Display all Blogs from the database
var query = from b in db.Blogs
orderby b.Name
select b;
Console.WriteLine("All blogs in the database:");
foreach (var item in query)
{
Console.WriteLine(item.Name);
}
Console.WriteLine("Press any key to exit...");
Console.ReadKey();
}
}
public class Blog
{
public int BlogId { get; set; }
public string Name { get; set; }
public virtual List<Post> Posts { get; set; }
}
public class Post
{
public int PostId { get; set; }
public string Title { get; set; }
public string Content { get; set; }
public int BlogId { get; set; }
public virtual Blog Blog { get; set; }
}
public class BloggingContext : DbContext
{
public DbSet<Blog> Blogs { get; set; }
public DbSet<Post> Posts { get; set; }
}

Answer 1

This actually doesn't have anything to do with your code. LocalDB will create a new database for you if one doesn't exist. The problem with removing the mdf/ldf files is that you're deleting the files without letting LocalDB know. So as far as it's concerned, the database still exists but the files backing the database are missing.
To delete a LocalDB database properly, use Server Explorer or SQL Object Explorer in Visual Studio (SQL Management Studio should work too). If the database file is in the app_data folder of your web project, deleting the file from Solution Explorer should properly delete the database as well.

Answer 2

What I was really trying to do was understand how/where a database is generated via a Code First approach. After some research, it turns out its pretty simple. All you need to do is create a connection string in your app.config or web.config file, something along the lines of ...
<connectionStrings>
<add name = YourDBContextName
providerName = "System.Data.SqlClient"
connectionString = "Data Source = (localdb)\v11.0; AttachDbFilename = Path to MDF file ...
The AttachDbFile specifies where the database will be created. You have to also name the connection the same as your database context.