EntityFramework 延时加载、事务、导航属性

//延时加载
    public class EFQueryAdvancedTest
    {
        public static void Show()
        {
            IQueryable<Llogin> sources = null;
            using (CodeFirst dbContext = new CodeFirst())
            {
                sources = dbContext.Set<Llogin>().Where(u => u.id1 > 3);

                var List = dbContext.Set<Llogin>().Where(u => u.id1 > 3);//1 这句话执行完，没有数据库查询

                foreach (var user in List)// 2 迭代遍历数据才去数据库查询--在真实需要使用数据时，才去数据库查询的
                {
                    Console.WriteLine(user.nameCH);
                }

                //这就是延迟查询,可以叠加多次查询条件，一次提交给数据库；可以按需获取数据；
                List = List.Where(u => u.id1 < 100);
                List = List.Where(u => u.DepartNumber == "01");
                List = List.OrderBy(u => u.id1);

                var list = List.ToList<Llogin>();//ToList()  迭代器  Count() FitstOrDefalut()

                //延迟查询也要注意：a 迭代使用时，用完了关闭连接  b 脱离context作用域
            }
            //foreach (var item in sources) //这个时候查询，已经超出作用域。会异常
            //{
            //    Console.WriteLine(item.nameCH);
            //}

            {
                {
                    List<int> intList = new List<int>() { 123, 4354, 3, 23, 3, 4, 4, 34, 34, 3, 43, 43, 4, 34, 3 };
                    var list = intList.Where(i =>
                    {
                        Thread.Sleep(1000);
                        return i > 10;
                    });//没有过滤
                    foreach (var i in list)//才去过滤
                    {
                        Console.WriteLine(i);
                    }
                    Console.WriteLine("*********************");
                    //这里是延迟的，利用的是迭代器的方式，每次去迭代访问时，才去筛选一次，委托+迭代器
                }
                //楼上是IEnumerable类型，数据其实已经在内存里，有个迭代器的实现，用的是委托
                //楼下的IQueryable类型，数据在数据库里面，这个list里面有表达式目录树---返回值类型--IQueryProvider(查询的支持工具，sqlserver语句的生成)
                //其实userList只是一个包装对象，里面有表达式目录树，有结果类型，有解析工具，还有上下文，真需要数据的时候才去解析sql，执行sql，拿到数据的---因为表达式目录树可以拼装；
                {
                    using (CodeFirst dbContext = new CodeFirst())
                    {
                        var list = dbContext.Set<Llogin>().Where(u => u.id1 > 10);

                        foreach (var item in list)
                        {
                            Console.WriteLine(item.nameCH);
                        }
                    }
                }
            }
        }
    }

/// 事务：1 SaveChange  
    ///       2 TransactionScope完成一个context的多次SaveChange
    ///       3 TransactionScope完成不同context实例的事务
    ///       4 通过context.Datebase.BeginTranscation
    public class ContextLifetimeTest
    {
        public static void Show()
        {
            #region 多个数据修改，一次SaveChange,开始事务保存
            using (CodeFirst dbContext = new CodeFirst())
            {
                Llogin llogin = new Llogin()
                {
                    id1 = 8,
                    name1 = "zhangsan",
                    nameCH = "张三",
                    psw = "/7k8sVej5hE=",
                    qx = "系统管理员",
                    department = "01",
                    TPFW = "0",
                    DepartNumber = "01"
                };

                Llogin Llogin3 = dbContext.L_login.FirstOrDefault(u => u.id1 == 3);
                Llogin3.nameCH += "aaa";

                Llogin Llogin4 = dbContext.L_login.FirstOrDefault(u => u.id1 == 4);
                Llogin4.nameCH += "bbb";

                //Llogin Llogin8 = dbContext.Set<Llogin>().Find(8);
                //dbContext.L_login.Remove(Llogin8);

                dbContext.SaveChanges();
            }
            #endregion


            #region 多个数据操作一次savechange，任何一个失败直接全部失败
            using (CodeFirst dbContext = new CodeFirst())
            {
                Llogin llogin = new Llogin()
                {
                    id1 = 8,
                    name1 = "zhangsan",
                    nameCH = "张三",
                    psw = "/7k8sVej5hE=",
                    qx = "系统管理员",
                    department = "01",
                    TPFW = "0",
                    DepartNumber = "01"
                };

                Llogin Llogin3 = dbContext.L_login.FirstOrDefault(u => u.id1 == 3);
                Llogin3.nameCH += "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";  //超过数据库字段长度

                Llogin Llogin4 = dbContext.L_login.FirstOrDefault(u => u.id1 == 4);
                Llogin4.nameCH += "bbb";

                dbContext.SaveChanges();
            }
            #endregion

            #region TransactionScope开启事务
            //using (CodeFirst dbContext = new CodeFirst())
            //{
            //    using (TransactionScope trans = new TransactionScope())
            //    {
            //        Llogin llogin = new Llogin()
            //        {
            //            id1 = 8,
            //            name1 = "zhangsan",
            //            nameCH = "张三",
            //            psw = "/7k8sVej5hE=",
            //            qx = "系统管理员",
            //            department = "01",
            //            TPFW = "0",
            //            DepartNumber = "01"
            //        };
            //        dbContext.L_login.Add(llogin);
            //        dbContext.SaveChanges();

            //        Llogin Llogin3 = dbContext.L_login.FirstOrDefault(u => u.id1 == 3);
            //        Llogin3.nameCH += "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";  //超过数据库字段长度
            //        dbContext.SaveChanges();

            //        trans.Complete();//能执行这个，就表示成功了；
            //    }

            //}
            #endregion

            #region 不同context实例 TransactionScope开启事务
            //using (CodeFirst dbContext = new CodeFirst())
            //using (CodeFirst dbContext1 = new CodeFirst())
            //{
            //    using (TransactionScope trans = new TransactionScope())
            //    {
            //        Llogin llogin = new Llogin()
            //        {
            //            id1 = 8,
            //            name1 = "zhangsan",
            //            nameCH = "张三",
            //            psw = "/7k8sVej5hE=",
            //            qx = "系统管理员",
            //            department = "01",
            //            TPFW = "0",
            //            DepartNumber = "01"
            //        };
            //        dbContext.L_login.Add(llogin);
            //        dbContext.SaveChanges();

            //        Llogin Llogin3 = dbContext1.L_login.FirstOrDefault(u => u.id1 == 3);
            //        Llogin3.nameCH += "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";  //超过数据库字段长度
            //        dbContext1.SaveChanges();

            //        trans.Complete();//能执行这个，就表示成功了；
            //    }

            //}
            #endregion

        }
    }

//导航属性加载&增加&删除
    public class NavigationTest
    {
        public static void ShowQuery()
        {
            //1 默认情况下，导航属性是延迟查询；
            //条件是virtaul属性+默认配置
            using (CodeFirst dbContext = new CodeFirst())
            {
                var departList = dbContext.Set<L_DepartMent>().Where(d => d.autoID == 1);
                foreach (var item in departList)//只查Depart
                {
                    Console.WriteLine(item.DepartMent);
                    foreach (var user in item.L_login)//使用再去查用户
                    {
                        Console.WriteLine(user.nameCH);
                    }
                }
            }
            //2 关闭延迟加载，子表数据就没了
            using (CodeFirst dbContext = new CodeFirst())
            {
                dbContext.Configuration.LazyLoadingEnabled = false;//关闭延迟查询
                var departList = dbContext.Set<L_DepartMent>().Where(d => d.autoID == 1);
                foreach (var item in departList)//只查Depart
                {
                    Console.WriteLine(item.DepartMent);
                    foreach (var user in item.L_login)//这里不会再去查询
                    {
                        Console.WriteLine(user.nameCH);
                    }
                }
            }
            //3 预先加载  Include 查询主表时就把子表数据一次性查出来
            //其实自己join也可以的
            using (CodeFirst dbContext = new CodeFirst())
            {
                dbContext.Configuration.LazyLoadingEnabled = false;//是否关闭无所谓
                var departList = dbContext.Set<L_DepartMent>().Include("L_login").Where(d => d.autoID == 1);
                foreach (var item in departList)//只查Depart
                {
                    Console.WriteLine(item.DepartMent);
                    foreach (var user in item.L_login)//这里不会再去查询
                    {
                        Console.WriteLine(user.nameCH);
                    }
                }
            }

            //4 关闭延迟查询后,如果需要子表数据，可以显示加载
            using (CodeFirst dbContext = new CodeFirst())
            {
                dbContext.Configuration.LazyLoadingEnabled = false;//是否关闭无所谓
                var departList = dbContext.Set<L_DepartMent>().Where(d => d.autoID == 1);
                foreach (var item in departList)//只查Depart
                {
                    Console.WriteLine(item.DepartMent);
                    dbContext.Entry<L_DepartMent>(item).Collection(c => c.L_login).Load();
                    foreach (var user in item.L_login)//这里不会再去查询
                    {
                        Console.WriteLine(user.nameCH);
                    }
                }
            }

        }


        public static void ShowInsert()
        {
            //数据插入：A表--B表(包含A的ID)--ID是自增的
            #region 一次savechange，如果是主外键，可以自动使用自增id；如果不是，就用不到
            {
                using (CodeFirst dbContext = new CodeFirst())
                {
                    L_AppMenu menu = new L_AppMenu()
                    {
                        MenuName = "测试",
                        ParentId = 0,
                        Icon = "icon-sys",
                        SquentIndex = 2,
                        NodeLeavel = 1,
                        IsShow = true,
                        TreeCode = "64"
                    };
                    dbContext.Set<L_AppMenu>().Add(menu);

                    L_User_Qx user_Qx = new L_User_Qx()
                    {
                        UserId = 1,
                        MenuId = menu.MenuId,
                        IsSearch = true,
                        IsSet = true
                    };
                    dbContext.Set<L_User_Qx>().Add(user_Qx);

                    dbContext.SaveChanges();
                }
            }
            #endregion
        }


        //1 数据库设置级联删除  只需要删除主表
        //2 如果没有级联删除--数据库外键设置强制外键约束为否--就可以只删除主表
        public static void ShowDelete()
        {
            string DepartNumber = "";
            {
                using (CodeFirst dbContext = new CodeFirst())
                {
                    L_DepartMent depart = new L_DepartMent()
                    {
                        DepartNumber = "05",
                        DepartMent = "测试123",
                        ParentId = "0"
                    };
                    dbContext.Set<L_DepartMent>().Add(depart);
                    dbContext.SaveChanges();

                    Llogin llogin = new Llogin()
                    {
                        name1 = "wangwu",
                        nameCH = "王五",
                        psw = "/7k8sVej5hE=",
                        qx = "系统管理员",
                        department = "01",
                        TPFW = "0",
                        DepartNumber = depart.DepartNumber
                    };

                    dbContext.Set<Llogin>().Add(llogin);
                    dbContext.SaveChanges();

                    DepartNumber = depart.DepartNumber;
                }
                using (CodeFirst dbContext = new CodeFirst())
                {
                    L_DepartMent departMent = dbContext.L_DepartMent.FirstOrDefault(l => l.DepartNumber == DepartNumber);
                    dbContext.Set<L_DepartMent>().Remove(departMent);
                    dbContext.SaveChanges();
                }
            }
        }
    }