树形结构数据存储方案（简单介绍）
方案1：继承关系驱动的schema设计
方案2：基于左右值编码的schema设计
在方案1的基础上计算左右值
/// <summary>
/// 计算树节点左右值
/// </summary>
/// <param name="trees">树节点集合</param>
/// <param name="parentid">父节点</param>
/// <param name="left">左值，初始为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;
}
