如何使用实体框架同时保存到数据库的两个表

嗨，我在同时保存数据库的两个表时遇到问题，但我的第一个表保存起来没有问题。第二个表与第一个表相关，并且已经具有FK。请帮忙。。这是我的密码。感谢

        //Save to Database
        //1st Table
        casecrawlerdbEntities1 db = new casecrawlerdbEntities1();
        document document = new document();
        document.DocumentNo = DocumentNo;
        document.Description = Description;
        document.Author = Author;
        document.PublishedDate = DateTime.Parse(PublishedDate); ;
        document.Summary = Summary;
        document.SearchKeys = richTextBox9.ToString();
        document.References = url;
        document.IsPublic = false;
        document.IsPublished = false;
        document.CreatedDate = DateTime.Now;
        db.documents.AddObject(document);
        db.SaveChanges();
        //2nd Table
        content content = new content();
        content.ContentType = ContentType;
        content.Content = Content;
        db.contents.AddObject(content);
        db.SaveChanges();
        MessageBox.Show("Saved to Database");

content.Document = document;