LINQ用于将两个列表与复杂实体进行比较

Question

我们有一个如下所列的课程结构

public class ItemDTO
{
    public int ItemID { get; set; }
}


public class CostPageDTO
{
    public string CostPageNumber { get; set; }
    public List<ItemDTO> Items { get; set; }
}

有两个列表 - 1）数据库中存在的Costpage和Items列表2）用户选择的costpages

问题

我们需要比较这两个列表并获得一个结果列表，其中包含成本页面，实际集合和选定集合中不同项目的计数相同。

这个best performing LINQ是什么（采用链式方法）？

预期结果

基于以下场景的预期结果是仅包含1个成本页的列表 - “C2”（项目匹配）

CODE

static void Main(string[] args)
{

    List<CostPageDTO> selectedCostPageAndItems = GetSelectedCostPageAndItems();
    List<CostPageDTO> actualItems = GetActualItems();

    //LINQ code to get the matching count costPages

}


private static List<CostPageDTO> GetSelectedCostPageAndItems()
{
    ItemDTO i1 = new ItemDTO();
    i1.ItemID = 1;

    ItemDTO i2 = new ItemDTO();
    i2.ItemID = 2;

    ItemDTO i3 = new ItemDTO();
    i3.ItemID = 3;


    CostPageDTO c1 = new CostPageDTO();
    c1.CostPageNumber = "C1";
    c1.Items = new List<ItemDTO>();
    c1.Items.Add(i1);

    CostPageDTO c2 = new CostPageDTO();
    c2.CostPageNumber = "C2";
    c2.Items = new List<ItemDTO>();
    c2.Items.Add(i2);
    c2.Items.Add(i3);

    //CostPageDTO c2Duplicate = new CostPageDTO();
    //c2Duplicate.CostPageNumber = "C2";
    //c2Duplicate.Items = new List<ItemDTO>();
    //c2Duplicate.Items.Add(i2);
    //c2Duplicate.Items.Add(i3);

    List<CostPageDTO> selectedCostPageAndItems = new List<CostPageDTO>();
    selectedCostPageAndItems.Add(c1);
    selectedCostPageAndItems.Add(c2);
    //selectedCostPageAndItems.Add(c2Duplicate);

    return selectedCostPageAndItems;

}
private static List<CostPageDTO> GetActualItems()
{
    ItemDTO i1 = new ItemDTO();
    i1.ItemID = 1;

    ItemDTO i2 = new ItemDTO();
    i2.ItemID = 2;

    ItemDTO i3 = new ItemDTO();
    i3.ItemID = 3;

    ItemDTO i3Duplicate = new ItemDTO();
    i3Duplicate.ItemID = 3;

    CostPageDTO c1 = new CostPageDTO();
    c1.CostPageNumber = "C1";
    c1.Items = new List<ItemDTO>();
    c1.Items.Add(i1);
    c1.Items.Add(i2);
    c1.Items.Add(i3);

    CostPageDTO c2 = new CostPageDTO();
    c2.CostPageNumber = "C2";
    c2.Items = new List<ItemDTO>();
    c2.Items.Add(i2);
    c2.Items.Add(i3);
    c2.Items.Add(i3Duplicate);

    List<CostPageDTO> actualItems = new List<CostPageDTO>();
    actualItems.Add(c1);
    actualItems.Add(c2);

    return actualItems;

}

Answer 1

这将选择您的预期结果：

方法语法：

var result = selectedCostPageAndItems.SelectMany(scp => actualItems.Where(acp=>acp.CostPageNumber == scp.CostPageNumber),
                            (scp,acp)=> new {CostPageNumber = scp.CostPageNumber,
                                        scpItems = new HashSet<int>(scp.Items.Select(x=>x.ItemID)),
                                        acpItems = new HashSet<int>(acp.Items.Select(x=>x.ItemID))})
                        .Where(x => x.scpItems.SetEquals(x.acpItems))
                        .Select(x => x.CostPageNumber);

查询理解语法：

var result = from cp1 in selectedCostPageAndItems
             from cp2 in actualItems
             let items1 = new HashSet<int>(cp1.Items.Select(x=>x.ItemID))
             let items2 = new HashSet<int>(cp2.Items.Select(x=>x.ItemID))
             where cp1.CostPageNumber == cp2.CostPageNumber
             && items1.SetEquals(items2)
             select cp1.CostPageNumber;

<强>解释

查找具有相同scp

的所有选定对（acp）和实际（CostPageDTO）CostPageNumber对

selectedCostPageAndItems.SelectMany(scp => actualItems.Where(acp=>acp.CostPageNumber == scp.CostPageNumber)

对于每对此类对（scp和acp），请为所选（CostPageNumber）和实际（ItemDTO.ItemID选择scpItems和一组acpItems（ CostPageDTO）(scp,acp)=> new {CostPageNumber = scp.CostPageNumber, scpItems = new HashSet<int>(scp.Items.Select(x=>x.ItemID)), acpItems = new HashSet<int>(acp.Items.Select(x=>x.ItemID))})

CostPageNumber

最后选择具有相同集合的Where(x => x.scpItems.SetEquals(x.acpItems)).Select(x => x.CostPageNumber)

{{1}}

HashSet的创建和比较全部是 O（n）