var user = db.UserInfos.FirstOrDefault(a => a.Id == 5);
                //会在sql代码中生成Street = "上海"代码
                var address1 = db.Entry(user).Collection(b => b.Address).Query().Where(p => p.Street == "上海" ).ToList();
                //会把所有的Street的代码都取回内存，然后在内存在再访问
                var address2 = user.Address.Where(p => p.Street == "上海").Count();