不包括使用linq的项目

本文关键字：项目 linq 不包括 | 更新日期: 2023-09-27 18:25:52

我有两个列表通过LINQ返回。我的目标是返回"defaults"列表中的所有项减去"notDefaults"列表的项。

我目前正在通过两个嵌套的for循环和使用RemoveAt来完成这项工作。这能只用一个LINQ语句完成吗？基本上，我需要"defaults"列表中的所有内容，除非该项存在于表"AssetPayrollMarkupOverrides"中。

我担心使用"RemoveAt"，因为它看起来很慢。

var defaults = (from a in dbcontext.Assets
    join b in dbcontext.AssetAddresses on a.AssetID equals b.AssetID
    join c in dbcontext.Addresses on b.AddressID equals c.AddressID
    join d in dbcontext.StateLookups on c.StateID equals d.StateID
    where d.ShortName == state
    select new AssetMarkup()
    {
        AssetId = a.AssetID,
        AssetName = a.AssetName,
        Seg1_Code = a.Seg1_Code,
    }).ToList();

var notDefaults = (from a in dbcontext.Assets
    join b in dbcontext.AssetAddresses on a.AssetID equals b.AssetID
    join c in dbcontext.Addresses on b.AddressID equals c.AddressID
    join d in dbcontext.StateLookups on c.StateID equals d.StateID
    join e in dbcontext.AssetPayrollMarkupOverrides on a.AssetID equals e.AssetID
    where d.ShortName == state
    select new AssetMarkup()
    {
        AssetId = a.AssetID,
        AssetName = a.AssetName,
        Seg1_Code = a.Seg1_Code,
        ShortName = d.ShortName,
        OfficePercentage = e.OfficePercentage,
        MaintenancePercentage = e.MaintenancePercentage,
        Note = e.Note
    }).ToList();

我最初是这样做的，以确保两个列表匹配：

var defaults = (from a in dbcontext.Assets
    join b in dbcontext.AssetAddresses on a.AssetID equals b.AssetID
    join c in dbcontext.Addresses on b.AddressID equals c.AddressID
    join d in dbcontext.StateLookups on c.StateID equals d.StateID
    where d.ShortName == state
    select new AssetMarkup()
    {
        AssetId = a.AssetID,
        AssetName = a.AssetName,
        Seg1_Code = a.Seg1_Code,
        ShortName = d.ShortName,
        OfficePercentage = dbcontext.PayrollMarkups.Where(x => x.StateID == c.StateID).Select(x => x.OfficePercentage).FirstOrDefault(),
        MaintenancePercentage = dbcontext.PayrollMarkups.Where(x => x.StateID == c.StateID).Select(x => x.MaintenancePercentage).FirstOrDefault(),
        Note = dbcontext.AssetPayrollMarkupOverrides.Where(x => x.AssetID == a.AssetID).Select(x => x.Note).FirstOrDefault()
    }).ToList();
var notDefaults = (from a in dbcontext.Assets
   join b in dbcontext.AssetAddresses on a.AssetID equals b.AssetID
   join c in dbcontext.Addresses on b.AddressID equals c.AddressID
   join d in dbcontext.StateLookups on c.StateID equals d.StateID
   join e in dbcontext.AssetPayrollMarkupOverrides on a.AssetID equals e.AssetID
   where d.ShortName == state
   select new AssetMarkup()
   {
       AssetId = a.AssetID,
       AssetName = a.AssetName,
       Seg1_Code = a.Seg1_Code,
       ShortName = d.ShortName,
       OfficePercentage = dbcontext.PayrollMarkups.Where(x => x.StateID == c.StateID).Select(x => x.OfficePercentage).FirstOrDefault(),
       MaintenancePercentage = dbcontext.PayrollMarkups.Where(x => x.StateID == c.StateID).Select(x => x.MaintenancePercentage).FirstOrDefault(),
       Note = dbcontext.AssetPayrollMarkupOverrides.Where(x => x.AssetID == a.AssetID).Select(x => x.Note).FirstOrDefault()
   }).ToList();
return Json(defaults.Except(notDefaults).OrderBy(x => x.AssetName).ToDataSourceResult(request));

不包括使用linq的项目

您可以使用Except

var remaining = defaults.Except(notDefaults);

您可能需要确保AssetMarkup上的相等比较器设置为以非基于引用的方式比较对象。

请参阅此处http://msdn.microsoft.com/en-us/library/ms173147（v=vs.80）.aspx

您要查找的是这两个集合的补码。LinqException（）方法就是为了做到这一点而设计的（您可以使用重载来获取IEqualityComparer）：

public class AssetMarkupComparer : IEqualityComparer<AssetMarkup>
{
    public bool Equals(AssetMarkup am1, AssetMarkup am2)
    {
        return am1.AssetId == am2.AssetId;
    }
    public int GetHashCode(AssetMarkup obj)
    {
        return obj.AssetId.GetHashCode();
    }
}
var complement = defaults.Except(notDefaults, new AssetMarkupComparer());

您需要考虑comparer方法中的null，但这只是一个骨架示例。

var notDefaultIds = notDefaults.Select(nd => nd.AssetID);
var result = defaults.Where(def => !notDefaultIds.Any(id => id == def.AssetID);

如果要减少数据库往返，请将ToList()从notDefaults、defaults移动到result；

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