using (var context = new BloggingContext())
{
    var blog = new Blog { Url = "http://sample.com" };
    context.Blogs.Add(blog);
    context.SaveChanges();
}

using (var context = new BloggingContext())
{
    var blog = context.Blogs.First();
    blog.Url = "http://sample.com/blog";
    context.SaveChanges();
}

using (var context = new BloggingContext())
{
    var blog = context.Blogs.First();
    context.Blogs.Remove(blog);
    context.SaveChanges();
}

using (var context = new BloggingContext())
{
    // add
    context.Blogs.Add(new Blog { Url = "http://sample.com/blog_one" });
    context.Blogs.Add(new Blog { Url = "http://sample.com/blog_two" });
    // update
    var firstBlog = context.Blogs.First();
    firstBlog.Url = "";
    // remove
    var lastBlog = context.Blogs.Last();
    context.Blogs.Remove(lastBlog);
    context.SaveChanges();
}

using (var context = new BloggingContext())
{
    var blog = new Blog
    {
        Url = "http://blogs.msdn.com/dotnet",
        Posts = new List<Post>
        {
            new Post { Title = "Intro to C#" },
            new Post { Title = "Intro to VB.NET" },
            new Post { Title = "Intro to F#" }
        }
    };
    context.Blogs.Add(blog);
    context.SaveChanges();
}

using (var context = new BloggingContext())
{
    var blog = context.Blogs.Include(b => b.Posts).First();
    var post = new Post { Title = "Intro to EF Core" };
    blog.Posts.Add(post);
    context.SaveChanges();
}

using (var context = new BloggingContext())
{
    //新增一個(gè)主體實(shí)體
    var blog = new Blog { Url = "http://blogs.msdn.com/visualstudio" };
    var post = context.Posts.First();
    //post更新關(guān)系
    post.Blog = blog;
    context.SaveChanges();
}

var blog = context.Blogs.Include(b => b.Posts).First();
var posts = blog.Posts.ToList();
DumpEntities("  After loading entities:", context, blog, posts);
context.Remove(blog);
DumpEntities($"  After deleting blog '{blog.BlogId}':", context, blog, posts);
try
{
    Console.WriteLine();
    Console.WriteLine("  Saving changes:");
    context.SaveChanges();
    DumpSql();
    DumpEntities("  After SaveChanges:", context, blog, posts);
}
catch (Exception e)
{
    DumpSql();
    Console.WriteLine();
    Console.WriteLine($"  SaveChanges threw {e.GetType().Name}: {(e is DbUpdateException ? e.InnerException.Message : e.Message)}");
}

After loading entities:
    Blog '1' is in state Unchanged with 2 posts referenced.
      Post '1' is in state Unchanged with FK '1' and reference to blog '1'.
      Post '2' is in state Unchanged with FK '1' and reference to blog '1'.

  After deleting blog '1':
    Blog '1' is in state Deleted with 2 posts referenced.
      Post '1' is in state Unchanged with FK '1' and reference to blog '1'.
      Post '2' is in state Unchanged with FK '1' and reference to blog '1'.

  Saving changes:
    DELETE FROM [Posts] WHERE [PostId] = 1
    DELETE FROM [Posts] WHERE [PostId] = 2
    DELETE FROM [Blogs] WHERE [BlogId] = 1

  After SaveChanges:
    Blog '1' is in state Detached with 2 posts referenced.
      Post '1' is in state Detached with FK '1' and no reference to a blog.
      Post '2' is in state Detached with FK '1' and no reference to a blog.

using (var context = new BloggingContext())
{
    using (var transaction = context.Database.BeginTransaction())
    {
        try
        {
            context.Blogs.Add(new Blog { Url = "http://blogs.msdn.com/dotnet" });
            context.SaveChanges();
            context.Blogs.Add(new Blog { Url = "http://blogs.msdn.com/visualstudio" });
            context.SaveChanges();
            var blogs = context.Blogs
                .OrderBy(b => b.Url)
                .ToList();
            // Commit transaction if all commands succeed, transaction will auto-rollback
            // when disposed if either commands fails
            transaction.Commit();
        }
        catch (Exception)
        {
            // TODO: Handle failure
        }
    }
}