做项目时经常遇到树状层级数据。从各个层级数据的转换查询等。场景如行业类别的多层级，行政区层级，检查项类别层级等等。

数据结构如  Id Name ParentId

#region area树状节点的转化        public List ConvertToLeafChildAreas(List
     
       areaIds)        {            var allAreas = GetNewAreas().ToList();            List
       leafChildren = new List
      ();            foreach (var areaId in areaIds)            {                leafChildren.AddRange(GetLeafChildAreas(areaId, allAreas));            }            return leafChildren;        }        /// 
      
        /// 根据父ID获取所有的最小地区        /// 
        /// 
              /// 
              /// 
              public List
       GetLeafChildAreas(int parentId,List
       allAreas)        {            List
       leafChildren = new List
      ();            var sons = allAreas.Where(o => o.ParentId == parentId).ToList();            if (sons.Any())            {                foreach (var item in sons)                {                    leafChildren.AddRange(GetLeafChildAreas(item.Id, allAreas));                }            }            else            {                var currentArea = allAreas.FirstOrDefault(m=>m.Id== parentId);                leafChildren.Add(currentArea);            }            return leafChildren;        }        public List
       ConvertToRootAreas(List
      
        childAreaIds)        {            var allAreas = GetNewAreas().ToList();            var childAreas = allAreas.Where(m => childAreaIds.Contains(m.Id)).ToList();            List
        root = new List
       ();            foreach (var childArea in childAreas)            {                root.Add(GetRootArea(childArea, allAreas));            }            return root.Distinct().ToList();        }        /// 
       
        /// 根据子ID获取所有的最顶级地区        /// 
        /// 
               /// 
               /// 
               public Area GetRootArea(Area childArea, List
        allAreas)        {            var parentArea = allAreas.FirstOrDefault(o => o.Id == childArea.ParentId);            if (parentArea==null) return childArea;            return GetRootArea(parentArea,allAreas);        }        #endregion