LINQ條件和

Question

我有與需要作爲一個「和」操作的匹配濾波器的一組陣列。餘的過濾器數組爲空應當interpreeted作爲包括用於該過濾器的所有內容：

List<string> cars = new List<string>(); 
List<string> flights = new List<string>(); 
      flights.Add("Boing"); 
      flights.Add("Airbus"); 

      var transports = new List<Transport>(); 
      var t1 = new Transport("Ford", "Boing"); 
      var t2 = new Transport("BMW", "Boing"); 
      var t3 = new Transport("BMW", "Flights INC"); 

      transports.Add(t1); 
      transports.Add(t2); 
      transports.Add(t3); 

      //returns 0 result. In this scenario I would expect to get all with boing and Airbus and cars excluded from search because its empty 
      var result = transports.Where(p => 
       (cars.Count>0 && cars.Contains(p.CarType)) && 
       (flights.Count > 0 && flights.Contains(p.FlightType))).ToList(); 


     cars = new List<string>(); 
      flights = new List<string>(); 
      cars.Add("BMW"); 
      flights.Add("Boing"); 

      IEnumerable<Transport> result2 = transports; 

      if (cars?.Any() == true) 
      { 
       result2 = transports.Where(p => cars.Contains(p.CarType)); 
      } 
      if (flights?.Any() == true) 
      { 
       result2 = transports.Where(p => flights.Contains(p.FlightType)); 
      } 

      // all rows returned here I only want t2 
      var r = result2.ToList(); 

的Rahul引導是在正確的方向。數組不能爲null。解決它：

     statusViewResult = statusViewResult.Where(p=> 
      (query.ClustersSelected.Count == 0 || query.ClustersSelected.Contains(p.Cluster)) && 
      (query.ParkNamesSelected.Count == 0 || query.ParkNamesSelected.Contains(p.ParkName))); 

Answer 1

那麼你可以使用複合條件像下面考慮ClustersSelected是數組類型

.Where(p => query.ClustersSelected.Length > 0 && query.ClustersSelected.Contains(p.Cluster) 

Answer 2

一個簡單的if會做到這一點：

if(query.ClustersSelected?.Any() == true) 
{ 
    statusViewResult = statusViewResult.Where(p => query.ClustersSelected.Contains(p.Cluster)); 
} 
if(query.ParkNamesSelected?.Any() == true) 
{ 
    statusViewResult = statusViewResult.Where(p => query.ParkNamesSelected.Contains(p.ParkName)); 
} 

每個考慮又增加了過濾器收集。我經常在Entity Framework（和IQueryable）中使用這樣的代碼來生成更小的SQL查詢，但它對於LINQ to object（IEnumerable）也同樣適用。
我使用ClustersSelected?.Any() == true搭上null屬性這兩種情況下，和一個空的集合。