对象的 LINQ 检查列表包含一个值而不是其他一些值

Posted 2023-02-15

【中文标题】对象的 LINQ 检查列表包含一个值而不是其他一些值

【英文标题】：LINQ check list of objects contain a value AND not some other values

【发布时间】：2022-01-04 14:48:32

【问题描述】：

假设我有这个对象列表：

var shipments = new List<ShipmentTracking>() 
    new ShipmentTracking() 
        trackingNumber = "32021001000", trackings = new List<Tracking>() 
            new Tracking()  trackingCode = "EBC", trackingPoint = "Entered", trackingDateTime = DateTime.Now, trackingMemo = "" 
        
    ,
    new ShipmentTracking() 
        trackingNumber = "32021001001", trackings = new List<Tracking>() 
            new Tracking()  trackingCode = "EBC", trackingPoint = "Entered", trackingDateTime = DateTime.Now.AddDays(1), trackingMemo = "" ,
            new Tracking()  trackingCode = "AWB", trackingPoint = "Registered", trackingDateTime = DateTime.Now.AddDays(1), trackingMemo = "" 
        
    ,
    new ShipmentTracking() 
        trackingNumber = "32021001002", trackings = new List<Tracking>() 
            new Tracking()  trackingCode = "EBC", trackingPoint = "Entered", trackingDateTime = DateTime.Now.AddDays(2), trackingMemo = "" ,
            new Tracking()  trackingCode = "AWB", trackingPoint = "Registered", trackingDateTime = DateTime.Now.AddDays(2), trackingMemo = "" ,
            new Tracking()  trackingCode = "DSP", trackingPoint = "Shipped", trackingDateTime = DateTime.Now.AddDays(2), trackingMemo = "" 
        
    ,
    new ShipmentTracking() 
        trackingNumber = "32021001003", trackings = new List<Tracking>() 
            new Tracking()  trackingCode = "EBC", trackingPoint = "Entered", trackingDateTime = DateTime.Now.AddDays(3), trackingMemo = "" ,
            new Tracking()  trackingCode = "AWB", trackingPoint = "Registered", trackingDateTime = DateTime.Now.AddDays(3), trackingMemo = "" ,
            new Tracking()  trackingCode = "DSP", trackingPoint = "Shipped", trackingDateTime = DateTime.Now.AddDays(3), trackingMemo = "" ,
            new Tracking()  trackingCode = "CCI", trackingPoint = "Cleared", trackingDateTime = DateTime.Now.AddDays(3), trackingMemo = "" 
        
    ,
    new ShipmentTracking() 
        trackingNumber = "32021001004", trackings = new List<Tracking>() 
            new Tracking()  trackingCode = "EBC", trackingPoint = "Entered", trackingDateTime = DateTime.Now.AddDays(4), trackingMemo = "" ,
            new Tracking()  trackingCode = "AWB", trackingPoint = "Registered", trackingDateTime = DateTime.Now.AddDays(4), trackingMemo = "" ,
            new Tracking()  trackingCode = "DSP", trackingPoint = "Shipped", trackingDateTime = DateTime.Now.AddDays(4), trackingMemo = "" ,
            new Tracking()  trackingCode = "CCI", trackingPoint = "Cleared", trackingDateTime = DateTime.Now.AddDays(4), trackingMemo = "" ,
            new Tracking()  trackingCode = "POD", trackingPoint = "Delivered", trackingDateTime = DateTime.Now.AddDays(4), trackingMemo = "" 
        
    
;

我需要只检查并返回具有 trackingCode == "DSP" 但不使用 "CCI" 或 "POD" trackingCode 的货件跟踪的查询，因此在此示例中使用跟踪号 32021001002 进行货件跟踪就是那个。

我试过了，但似乎没有用：

foreach (var shipment in shipments)

    var foo = shipment.trackings.FirstOrDefault((t => t.trackingCode == "DSP" && t.trackingCode != "CCI"));

    if (shipment.trackings.Contains(foo))
    
        
    

感谢任何帮助或指针。 谢谢！

【问题讨论】：

t.trackingCode == "DSP" && t.trackingCode != "CCI" - 第二个谓词是多余的。如果 TrackingCode 等于“DSP”，则它自动不等于“CCI”。您犯了一个典型的错误，即（作为人类）查看跨行的值，但编写的代码比较同一行中的值

【参考方案1】：

您希望在跟踪列表中发货：有任何跟踪代码“DSP”并且没有任何跟踪代码“CCI”

shipments.Where(s => 
  s.Trackings.Any(t => t.TrackingCode == "DSP") && 
  !s.Trackings.Any(t => t.TrackingCode == "CCI")
);

你也可以这样写：

shipments.Where(s => 
  s.Trackings.Any(t => t.TrackingCode == "DSP") && 
  s.Trackings.All(t => t.TrackingCode != "CCI")
);

即有任何跟踪代码是 DSP 且所有跟踪代码都不是 CCI 的货件"

使用对你更有意义的那个

【参考方案2】：

有 trackingCode == "DSP" 但没有使用 "CCI" 或 “豆荚”

我会填写两个集合以简化它并使其易于更改：

var validCodes = new List<string>"DSP";
var invalidCodes = new List<string>"CCI", "POD";

如果您想忽略大小写，那么将dsp 和DSP 视为您需要StringComparer.OrdinalIgnoreCase，否则StringComparer.Ordinal。

查询很简单：

List<ShipmentTracking> trackingList = shipments
    .Where(st => st.trackings.Any(t => validCodes.Contains(t.trackingCode, StringComparer.OrdinalIgnoreCase)))
    .Where(st => !st.trackings.Any(t => invalidCodes.Contains(t.trackingCode, StringComparer.OrdinalIgnoreCase)))
    .ToList();

除了两个Where，您还可以将一个与&& 一起使用。我更喜欢两个，因为它更容易阅读。