.NET Entity Framework基本使用方法

            //普通查询 Linq 方式
            IQueryable<Book> list = from b in db.Set<Book>()
                       where b.BookId > 5 && b.TypeId == 3
                       select b;
            //普通查询 Lambda 方式
            IQueryable<Book> list1 = db.Set<Book>()
                .Where(b => b.BookId > 5 && b.TypeId == 3);

            //多表查询 Linq
            var list = from book in db.Set<Book>()
                       join bookType in db.Set<BookType>()
                       on book.TypeId equals bookType.TypeId
                       select new
                       {
                           book
                       };

            //多表查询 lambda
            var list = db.Set<Book>()
                .Where(u => u.BookId > 2 && u.TypeId == 4)
                .Join(db.Set<BookType>(), book => book.TypeId, tp => tp.TypeId, (book, tp) => new { book, tp });

            //延迟加载 使用时才查询数据库  没用一次就查一次
            IQueryable<Book> list = db.Set<Book>()
                .OrderByDescending(u => u.BookId)    //IQueryable对象中Expression方法默认将Lambda表达式转换成Expression对象
                .Skip(2)
                .Take(3);

            //不具备延迟加载，因为IEnumerable没有方法去拼接完整sql语句
            IEnumerable<Book> list1 = db.Set<Book>()
                .AsEnumerable()   //把结果强转成 IEnumerable 类型
                .OrderByDescending(u => u.BookId)
                .Skip(2)
                .Take(3);

        [HttpPost]
        public ActionResult Add(Book book)
        {
            DbContext db = new DbModel();
            db.Set<Book>().Add(book);
            //返回受影响行数
            if(db.SaveChanges() > 0)
            {
                return Json(new
                {
                    msg = "添加成功"
                });
            }else
            {
                return Json(new
                {
                    msg = "添加失败"
                });
            }
        }

        [HttpPost]
        public ActionResult Edit(Book bb) {
            DbContext db = new DbModel();
            //将对象附加到上下文  状态设置为未更改
            db.Set<Book>().Attach(bb);
            db.Entry(bb).State = EntityState.Modified;
            db.SaveChanges();
            return Json(new
            {
                msg = "修改成功"
            });
        } 

        public ActionResult Delete(int id) {
            DbContext db = new DbModel();
            Book book = db.Set<Book>().FirstOrDefault(b => b.BookId == id);
            db.Set<Book>().Remove(book);
            db.SaveChanges();
            return Json(new
            {
                msg = "删除成功"
            },JsonRequestBehavior.AllowGet);
        }