记一则 Lambda内递归调用方法将集合对象转换成树形结构

 public dynamic GetDepartments(string labID)
        {
            List<int> usedIDs = new List<int>(); //缓存已用过的ID

            //定义递归算法
            Func<object,List<DepartmentItem>, List<DepartmentItem>, dynamic> recursion = (r,d,a) =>
            {
                List<dynamic> dyData = new List<dynamic>();
                if (d.Count > 0)
                {
                    d.ForEach(x =>
                    {
                        if (!usedIDs.Contains(x.DepartmentID))
                        {
                            dynamic department = new ExpandoObject();
                            department.DepartmentID = x.DepartmentID;
                            department.DepartmentName = x.DepartmentName;
                            department.DepartmentDesc = x.DepartmentDesc;
                            department.CreateTime = x.CreateTime;
                            department.ParentDepartmentID = x.ParentDepartmentID;
                            usedIDs.Add(x.DepartmentID);
                           // department.children = recursion(r, d, a); 这里直接调用的话会提示未定义变量，因为func的定义还没结束..
                           // 所以用以下的方法：调用的时候用object把方法传进来,然后转换下再调用执行；
                            var func_recursion = r as Func<object, List<DepartmentItem>, List<DepartmentItem>, dynamic>;
                            department.children = func_recursion(r, a.Where(w => w.ParentDepartmentID == x.DepartmentID).ToList(), a);
                            dyData.Add(department);
                        }
                    });
                }

                return dyData;
            };
            var departments =.....//获取集合数据;

            //调用方法
            //这里第一个参数就是方法的本身，传递进去进行递归调用
            var result = recursion(recursion, departments, departments);

            return result;

        }

　　代码是将集合对象转换成树形结构