Save a list one time in EF 6 Code First

Question

In the famous Blog/Post example, we see that how Blog entity is saved.

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; } 
}

Save Blog is simple:

        var blog = new Blog { Name = name }; 
        db.Blogs.Add(blog); 
        db.SaveChanges(); 

But I am not sure how to save Post since it is a List.

What I did was:

            foreach (var item in Posts)
            {
                Post p = new Post();
                p.Title = item.Title;
                p.Content = item.Content;
                SaveChanges();
            }

It works out of course, but if Posts contains many items then we have to save many times. It is inefficient, how can we save it just once?

Answer 1

There's two ways you can do this, either by adding to blog.Posts and having Entity Framework setup the foreign keys automatically:

Blog blog = new Blog 
{ 
    Name = name,
    Posts = new List<Post>()
}; 

foreach (var item in posts)
{
    Post p = new Post();
    p.Title = item.Title;
    p.Content = item.Content;

    blog.Posts.Add(p);
}

db.Blogs.Add(blog); 
db.SaveChanges(); 

or by adding to the Posts table directly:

// assuming you have a reference to the blog id in blogId

foreach (var item in posts)
{
    Post p = new Post();
    p.BlogId = blogId;
    p.Title = item.Title;
    p.Content = item.Content;

   db.Posts.Add(p);
}

db.SaveChanges();

You can add as many items as you'd like, but then call SaveChanges() once, and it'll only make one trip to the database.