EF 6 optional FK , delete still produces error - entity-framework

Question

So i have these two simple models
public class Blog
{
public int BlogId { get; set; }
private string _Name;
[Column("sNameColumn")]
public string Name { get { return _Name; } set { _Name = value; } }
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? blog_id { get; set; }
[ForeignKey("blog_id")]
public virtual Blog Blog { get; set; }
}
I haven't done anything unusual at the dbContext definition. Then , i try to do something like this.
db.Blogs.Remove(db.Blogs.Find(2));
db.SaveChanges();
And i get a FK violation error.Notice that the FK blog_id is null-able, so i thought that EF whould handle the delete, and make the corresponding FK Null.
Can you tell me what i am missing?

Answer 1

The entities have to be loaded for EF to be able to handle setting their foreign key to null.
var b = db.Blogs.Find(2);
db.Entry(b).Collection(b => b.Posts).Load();
db.Blogs.Remove(b);
db.SaveChanges();

Answer 2

Keep in mind that Entity Framework can only update entities it has loaded.
Of course there are ways to update database records by raw SQL statements that you can also execute through EF, but that's not the core of EF as ORM.
So if you want to use EF only, you have no choice. You have to load collections in Blogs explicitly for them to get dissociated from their parent. For instance by Include:
var b = db.Blogs.Include(b => b.Posts).Include(b => b.Comments)
.Single(b => b.BlogId == 2);
db.Blogs.Remove(b);
db.SaveChanges();
Or by Load as in the other answer.
Another option could be to use Entity Framework Extented. One of its features is batch updates, which allows one-shot update statements of records in an IQueryable given a template record. This would look like this:
using EntityFramework.Extensions;
...
db.Posts.Where(p => p.BlogId == 2)
.Update(p => new Post { BlogId = default(int?) });
db.Blogs.Remove(b);
db.SaveChanges();
Only the properties that are set in the template record are modified. To make this transactional, you should wrap all statements in a TransactionScope.