樹結構中的左右值計算

樹形結構數據存儲方案（簡單介紹）

方案1：繼承關系驅動的Schema設計

• 優點：直觀
• 缺點：查詢效率低

方案2：基於左右值編碼的Schema設計

• 優點：查詢效率高，無需遞規
• 使用參考

在方案1的基礎上計算左右值

        /// <summary>
        /// 計算樹節點左右值
        /// </summary>
        /// <param name="trees">樹節點集合</param>
        /// <param name="parentId">父節點</param>
        /// <param name="left">左值，初始為1</param>
        /// <returns></returns>
        private async Task<int> CalcLeftAndRight(IEnumerable<ProjectTreeDto> trees, string parentId, int left)
        {
            var right = left + 1;
            var result = trees.Where(q => q.ParentId.ToString() == parentId).ToList();
            for (int i = 0; i < result.Count(); i++)
            {
                right = await CalcLeftAndRight(trees, result[i].Id.ToString(), right);
            }

            StringBuilder sql = new StringBuilder();
            sql.Append($"update project_trees set LeftValue = {left}, RightValue = {right} where Id = '{parentId}'");

            await _dbContext.Database.ExecuteSqlCommandAsync(sql.ToString());

            return right + 1;
        }