Net 6.0层级数据转换：嵌套If转LINQ与Lambda优化

需求背景 #

基于Net 6.0环境，需要将特定格式的层级记录转换为度量布局格式。

原始输入格式 #

AAA|0000A|000AA|0001A
AAA|0000A|000AA|0002A
AAA|0000A|000AB|0001B
AAA|0000A|000AB|0002B
AAA|0000B|000BA|0001A
AAA|0000B|000BB|0001B

期望输出格式 #

AAA|BLANK|BLANK|BLANK

AAA|0000A|BLANK|BLANK
AAA|0000B|BLANK|BLANK

AAA|0000A|000AA|BLANK
AAA|0000A|000AB|BLANK
AAA|0000B|000BA|BLANK
AAA|0000B|000BB|BLANK

AAA|0000A|000AA|0001A
AAA|0000A|000AA|0002A
AAA|0000A|000AA|0003A
AAA|0000A|000AA|0004A
AAA|0000A|000AB|0001B
AAA|0000A|000AB|0002B
AAA|0000B|000BA|0001A
AAA|0000B|000BB|0001B

自定义对象定义 #

定义HierarchyStructure类用于承载层级数据：

public class HierarchyStructure
{
    public string Employer { get; set; }
    public string Level1 { get; set; }
    public string Level2 { get; set; }
    public string Level3 { get; set; }
    public string Level4 { get; set; }
    public bool isRxlvl3 { get; set; }
    public bool isExpired { get; set; }
    public string lvl4SubType { get; set; }

    public HierarchyStructure(string employer,
                              string? level1 = null,
                              string? level2 = null,
                              string? level3 = null,
                              string? level4 = null,
                              bool isRxlvl3 = false,
                              bool isExpired = false,
                              string? lvl4SubType = null)
    {
        this.Employer = employer;
        this.Level1 = string.IsNullOrEmpty(level1) ? string.Empty : level1;
        this.Level2 = string.IsNullOrEmpty(level2) ? string.Empty : level2;
        this.Level3 = string.IsNullOrEmpty(level3) ? string.Empty : level3;
        this.Level4 = string.IsNullOrEmpty(level4) ? string.Empty : level4;
        this.isRxlvl3 = isRxlvl3;
        this.isExpired = isExpired;
        this.lvl4SubType = string.IsNullOrEmpty(lvl4SubType) ? string.Empty : lvl4SubType;
    }
}

初始实现问题 #

通过两个只读属性获取层级数据列表：

private List<HierarchyStructure> AllLevels => _allLevels;
private List<HierarchyStructure> LocationLevels => _LocationLevels;

最初为每个层级单独编写去重数据获取方法，但方法逻辑重复，无法合并为递归或动态方法：

public bool GetDistinctEmployers()
{
    var selectedLevels = (from levels in AllLevels
                          select new HierarchyStructure(levels.Employer));

    foreach(HierarchyStructure level in selectedLevels) LocationLevels.Add(level);

    return true;
}

public bool GetDistinctLevel1(string emp)
{
    var selectedLevels = (from levels in AllLevels
                          where levels.Employer == emp
                          select new HierarchyStructure(levels.Employer,levels.Level1));

    foreach(HierarchyStructure level in selectedLevels) LocationLevels.Add(level);

    return true;
}

public bool GetDistinctLevel2(string lvl)
{
    var selectedLevels = (from levels in AllLevels
                          where levels.Level1 == lvl
                          select new HierarchyStructure(levels.Employer,levels.Level1, levels.Level2));

    foreach(HierarchyStructure level in selectedLevels) LocationLevels.Add(level);

    return true;
}

public bool GetDistinctLevel3(string lvl)
{
    var selectedLevels = (from levels in AllLevels
                          where levels.Level2 == lvl
                          select new HierarchyStructure(levels.Employer,levels.Level1, levels.Level2, levels.Level3));

    foreach(HierarchyStructure level in selectedLevels) LocationLevels.Add(level);

    return true;
}

public bool GetDistinctLevel4(string lvl)
{
    var selectedLevels = (from levels in AllLevels
                          where levels.Level3 == lvl
                          select new HierarchyStructure(levels.Employer,levels.Level1, levels.Level2, levels.Level3, levels.Level4));

    foreach(HierarchyStructure level in selectedLevels) LocationLevels.Add(level);

    return true;
}

尝试合并方法时，代码嵌套过深，触发流水线质量门告警：

public void ProcessLevels()
{
    if(GetDistinctEmployers())
    {
        foreach(string employer in AllLevels.Select(x => x.Employer))
        {
            if(GetDistinctLevel1(employer))
            {
                foreach(string level1 in AllLevels.Select(x => x.Level1))
                {
                    if(GetDistinctLevel2(level1))
                    {
                        foreach(string level2 in AllLevels.Select(x => x.Level2))
                        {
                            if(GetDistinctLevel3(level2))
                            {
                                foreach(string level3 in AllLevels.Select(x => x.Level3))
                                {
                                    if(GetDistinctLevel4(level3))
                                    {
                                        SaveData();
                                    }
                                }
                            }
                        }
                    }
                }
            }
        }
    }
}

同时代码质量提示指出AllLevels.Select(x => x.Employer)这类表达式可通过LINQ简化，但不清楚具体操作方式。期望输出为层级展开视图，包含从顶层到最底层的所有去重节点。

最终解决方案 #

参考建议后重构代码，消除大量嵌套循环，实现如下：

public void ProcessLevels()
{
    var employers = AllLevels.Where(x=> !x.isExpired ).Select(x => x.Employer).Distinct();
    var lvl1 = AllLevels.Where(x=> !x.isExpired ).Select(x => new {x.Employer, x.Level1 }).Distinct();
    var lvl2 = AllLevels.Where(x=> !x.isExpired ).Select(x => new {x.Employer, x.Level1, x.Level2 }).Distinct();
    var lvl3 = AllLevels.Where(x=> !x.isExpired ).Select(x => new {x.Employer, x.Level1, x.Level2, x.Level3 }).Distinct();
    var lvl4 = AllLevels.Where(x=> !x.isExpired ).Select(x => new {x.Employer, x.Level1, x.Level2, x.Level3, x.Level4 }).Distinct();

    foreach(var emp in employers) { LocationLevels.Add(new LevelHierarchyStructure(emp)); }
    foreach(var lvl in lvl1) { LocationLevels.Add(new LevelHierarchyStructure(lvl.Employer, lvl.Level1)); }
    foreach(var lvl in lvl2) { LocationLevels.Add(new LevelHierarchyStructure(lvl.Employer, lvl.Level1, lvl.Level2)); }
    foreach(var lvl in lvl3) { LocationLevels.Add(new LevelHierarchyStructure(lvl.Employer, lvl.Level1, lvl.Level2, lvl.Level3)); }
    foreach(var lvl in lvl4) { LocationLevels.Add(new LevelHierarchyStructure(lvl.Employer, lvl.Level1, lvl.Level2, lvl.Level3, lvl.Level4)); }

    SaveData();
}

内容的提问来源于stack exchange，提问作者Nyra