deptsNew = deptsNew.Where(a => a.Id < 0)

Question

因为deptsNew 要进行 Except 集合操作，所以当deptArr=null时，我要让deptsNew.count=0
通过deptsNew = deptsNew.Where(a => a.Id < 0)，id是自增长。还有什么其他方法让deptsNew.count=0吗？
                    var deptsNew = db.Department.AsQueryable();
                    if (deptArr != null)                        //添加：用户-部门-权限树
                    {
                        deptsNew = deptsNew.Where(a => deptArr.Contains(a.Id));                                   //用户提交-集合
                    }
                    else
                    {
                        deptsNew = deptsNew.Where(a => a.Id < 0);
                        
                    }

Answer 1

deptsNew = deptsNew.Where(a => a.Id < 0 or a.Id==null); 这样不可以吗？

Answer 2

可以直接判断deptArr 是否为null，如果为null,也无需Except ，直接返回集合

Answer 3

deptsNew = new Queryable()

Answer 4

因为下边有些代码：
        public static bool EditUser(RegisteredUsers user, int[] deptArr = null)
        {
            try
            {
                using (var db = new WEBVODEntities())
                {
                    var oldUser = db.RegisteredUsers.SingleOrDefault(a => a.Id == user.Id);
                    oldUser.RealName = user.RealName;
                    oldUser.RoleId = user.RoleId;
                    oldUser.DepartmentId = user.DepartmentId;
                    var deptsNew = db.Department.AsQueryable();
                    if (deptArr != null)                        //添加：用户-部门-权限树
                    {
                        deptsNew = deptsNew.Where(a => deptArr.Contains(a.Id));                                   //用户提交-集合
                    }
                    else
                    {
                        deptsNew = deptsNew.Where(a => a.Id < 0);
                        
                    }
                        var deptsOld = db.Manager.Where(a => a.LoginName == oldUser.LoginName).Select(a => a.Department);  //数据库-集合                        var deptsAdd = deptsNew.Except(deptsOld);//.ToList();                                                 //需要添加-集合
                        var deptsCut = deptsOld.Except(deptsNew);//.ToList();                                                 //需要删除集合                        foreach (var dept in deptsAdd)
                        {
                            Manager manager = new Manager();
                            manager.Department = dept;
                            manager.RegisteredUsers = oldUser;
                            manager.ManCreate = CurrentProject.GetCurrentUser().LoginName;
                            manager.TimeCreate = DateTime.Now;
                        }                        List<int> deptIdList = deptsCut.Select(a => a.Id).ToList();
                        var managersOld = db.Manager.Where(a => a.LoginName == oldUser.LoginName).Where(a => deptIdList.Contains(a.DeptId)).ToList();
                        foreach (var manager in managersOld)
                        {
                            db.Manager.DeleteObject(manager);
                        }
                    
                    db.SaveChanges();                    return true;
                }
            }
            catch
            { 
            }            return false;            
        }

Answer 5

用一个永远为false的条件不就行了……
deptsNew = deptsNew.Where(a => 1 == 2);  

Answer 6

这个不行错误 2 无法创建静态类“System.Linq.Queryable”的实例 F:\win2008iis\BYVOD\Models\RegisteredUserBLL.cs 103 36 BYVOD

Answer 7

这个不行错误 2 无法创建静态类“System.Linq.Queryable”的实例 F:\win2008iis\BYVOD\Models\RegisteredUserBLL.cs 103 36 BYVOD
我这么写你别这么写啊。。我错了。。我的意思是要你根据db.Department的类型new一个新的序列。