using (var context = new EFContext())
{
//方式一
var entity = context.Citys.Find(4);
context.Citys.Attach(entity);
entity.Name = "肇庆";
context.SaveChanges();
}

using (var context = new EFContext())
{//方式二var model = context.Citys.Find(5);model.Name = "潮州";context.Entry(model).State = System.Data.Entity.EntityState.Modified;context.SaveChanges();
}

 using (var db = new DBModel()){var student = db.students.FirstOrDefault(s => s.name == "萝莉");student.age = 13;   //将萝莉的年龄改为13岁
            db.SaveChanges();}

 using (var db = new DBModel()){var student = db.students.FirstOrDefault(s => s.name == "萝莉");    //查找萝莉db.students.Remove(student);    //删除萝莉
            db.SaveChanges();}

using (var db = new DBModel())  //创建数据库上下文
{//同步的方式执行SQL，并返回受影响的行数int result = db.Database.ExecuteSqlCommand(@"CREATE TABLE `test`.`test` (`id` INT NOT NULL,PRIMARY KEY(`id`)); ");//使用SqlParameter传值可以避免SQL注入var p_name = new SqlParameter("@name", "萝莉");var p_age = new SqlParameter("@age", 13);//如果使用的是MySql数据库 需要SqlParameter把替换为MySqlParameter//var p_name = new MySqlParameter("@name", "萝莉");//var p_age = new MySqlParameter("@age", 13);//更改学生年龄result = db.Database.ExecuteSqlCommand(@"UPDATE `test`.`student`SET `age` = @ageWHERE `name` = @name;", p_age, p_name);//异步的方式执行SQL，并返回受影响的行数Task<int> result2 = db.Database.ExecuteSqlCommandAsync("DROP TABLE `test`.`test`;");
}

using (var db = new DBModel())  //创建数据库上下文
{//查询叫萝莉的学生信息，并修改她的年龄student result1 = db.students.SqlQuery("SELECT  * FROM test.student WHERE name = '萝莉'").FirstOrDefault();result1.age = 13;   //通过实体集合下.SqlQuery查询到的数据，修改之后是可以保存到数据库的student result2 = db.Database.SqlQuery<student>("SELECT  * FROM test.student WHERE name = '旺财'").FirstOrDefault();result2.age = 21;   //因为使用的是.Database.SqlQuery查询到的，所以这里的修改不会保存到数据库//如果希望.Database.SqlQuery下查出的数据在修改后也能保存到数据库student result3 = db.Database.SqlQuery<student>("SELECT  * FROM test.student WHERE name = '小明'").FirstOrDefault();result3.age = 36;db.Entry<student>(result3).State = System.Data.Entity.EntityState.Modified; //通知数据上下文，这条记录也被修改了
    db.SaveChanges();
}