First let's create a table in our database that's called Person.

create table Person(
PersonID int primary key identity(1,1),
Name nvarchar(256)
)

Now drag a TextBox control to your design and change the AutoCompleteMode property. We'll be using the Suggest option.

Next, change the AutoCompleteSource to CustomSource.

Ok, great!

Now, using Entity Framework 4, we'll retrieve a list of Names from the database.

AutoCompleteStringCollection names = new AutoCompleteStringCollection();

private void MainForm_Load(object sender, EventArgs e)
{
    OurEntities db = new OurEntities();
    var peopleFromDatabase = db.People;
    foreach (var p in peopleFromDatabase)
    {
        names.Add(p.Name);
    }

    textBox1.AutoCompleteCustomSource = names;
}

And that wraps it up! You now have an autocomplete textbox.

I'd like to ask the community where would the best place to actually retrieve the information be? On KeyDown? But that would hammer the database a lot. Maybe on a Timer, refresh the list of known names?

Let's brainstorm!