在Linq選擇嵌套數組

Question

我想填充LINQ包含嵌套類數組的實例。我已經設法用下面的LINQ來做到這一點。我還包括組成該實例的類。

select new EditableWarrantBook { 
     Id = p1.id, 
     Comment = p1.EntryComment, 
     WarrantYear1 = new BookYear { 
      StatusYear = p2.StatusYear, 
      Status = p2.Status, 
     }, 
     WarrantYear2 = new BookYear { 
      StatusYear = p3.StatusYear, 
      Status = p3.Status, 
     }, 
     WarrantYear3 = new BookYear { 
      StatusYear = p4.StatusYear, 
      Status = p4.Status, 
     } 
    } 

public class EditableWarrantBook 
{ 
    public int Id { get; set; } 
    public string Comment { get; set; } 

    public BookYear[] WarrantYear = new BookYear[3]; 

    public BookYear WarrantYear1 
    { 
     get { return WarrantYear[0]; } 
     set { WarrantYear[0] = value; } 
    } 
    public BookYear WarrantYear2 
    { 
     get { return WarrantYear[1]; } 
     set { WarrantYear[1] = value; } 
    } 
    public BookYear WarrantYear3 
    { 
     get { return WarrantYear[2]; } 
     set { WarrantYear[2] = value; } 
    } 

} 

public class BookYear 
{ 
    public int? StatusYear { get; set; } 
    public string Status { get; set; } 
} 

這工作我可與WarrantYear[0]或WarrantYear1訪問值。這在設計UI時有時會很有用。但是，在這種情況下，我不需要WarrantYear1屬性，因爲我將其轉換爲JSON，並且不需要重複（或者想要在網絡上發送相同數據的兩個版本）。我的問題是，如何編寫select語句來加載WarrantYear數組。或者，我該如何編寫該類，以便可以將該數組作爲屬性訪問。我的解決方案不應包含EditableWarrantBook類中的Warrant1, Warrant2, Warrant3屬性。

Answer 1

問題是，你正試圖將SQL世界（構建你的查詢）與你的CLR世界混合（創建新對象）。解決這個問題的方法是將您的查詢分解爲您的初始數據提取查詢（SQL世界），然後枚舉結果以轉換爲您的對象（CLR世界）：

因此，在where p1.SaleYear == 2009之後，添加此：

select new { p1, p2, p3, p4 }) 
.AsEnumerable() 
.Select(tr => new EditableWarrantBook 
    { 
    Id = tr.p1.id, 
    Comment = tr.p1.EntryComment, 
    WarrantYear = new[] { 
     tr.p2 == null ? (BookYear)null : new BookYear // EDITED LINE 
     { 
      StatusYear = tr.p2.StatusYear, 
      Status = tr.p2.Status, 
     }, 
     tr.p3 == null ? (BookYear)null : new BookYear // EDITED LINE 
     { 
      StatusYear = tr.p3.StatusYear, 
      Status = tr.p3.Status, 
     }, 
     tr.p4 == null ? (BookYear)null : new BookYear // EDITED LINE 
     { 
      StatusYear = tr.p4.StatusYear, 
      Status = tr.p4.Status, 
     }} 
    }).ToList(); 

如果你想留在查詢語法，然後只需將其更改爲：

result = from tr in 
    (/*Select up to the AsEnumerable call above)*/).AsEnumerable() 
    select new EditableWarrantBook 
     { 
      /* Initialization code supplied above */ 
     } 

編輯：所以，我已經修改了例如一個更多的時間。它看起來像你回來的價值之一是空的，所以我已經添加了空檢查，以確保你沒有訪問空對象的屬性（雖然我沒有檢查爲空p1）。

Answer 2

由於我無法讓選擇工作沒有Warrant1，Warrant2和Warrant3屬性，我將它保留原樣並重寫了該類，以便JSON序列化程序將創建沒有Warrant1，Warrant2和Warrant3屬性的JSON實例。文章中使用了this的反思。爲了澄清問題，我第一次嘗試創建的JSON有效負載是原來的兩倍，因爲JSON序列化器同時創建了Warrant1，Warrant2和Warrant3結構以及Warrant []數組。用只有Warrant []數組的JSON結果的基類重寫該類才能滿足Web服務的接口要求。

namespace my.Models 
{ 
public class WarrantBook 
{ 
    public int Id { get; set; } 
    public string Comment { get; set; } 

    BookYear[] warrantYear = new BookYear[3]; 

    public BookYear[] WarrantYear 
    { 
     get { return warrantYear; } 
     set { warrantYear = value; } 
    } 
} 

public class EditableWarrantBook : WarrantBook 
{ 
    public BookYear WarrantYear1 
    { 
     get { return WarrantYear[0]; } 
     set { WarrantYear[0] = value; } 
    } 
    public BookYear WarrantYear2 
    { 
     get { return WarrantYear[1]; } 
     set { WarrantYear[1] = value; } 
    } 
    public BookYear WarrantYear3 
    { 
     get { return WarrantYear[2]; } 
     set { WarrantYear[2] = value; } 
    } 

} 
public class BookYear 
{ 
    public int? StatusYear { get; set; } 
    public string Status { get; set; } 
} 

public static class Ext 
{ 
    public static void CopyProperties(this EditableWarrantBook source, WarrantBook destination) 
    { 
     // Iterate the Properties of the destination instance and 
     // populate them from their source counterparts 
     PropertyInfo[] destinationProperties = destination.GetType().GetProperties(); 
     foreach (PropertyInfo destinationPi in destinationProperties) 
     { 
      PropertyInfo sourcePi = source.GetType().GetProperty(destinationPi.Name); 
      destinationPi.SetValue(destination, sourcePi.GetValue(source, null), null); 
     } 
    } 
} 

}

使用WCF REST web服務

 [WebGet(UriTemplate = "GetWarrant?id={s}&user={user}")] 
    public WarrantBook GetWarrant(string s, string user) 
    { 
     int id; 
     if (int.TryParse(s, out id)) 
     { 
      EditableWarrantBook model = SessionWarrantBook.One(p => p.Id == id); 
      model.CheckedOutBy = user; // need to add checkout code 
      WarrantBook jsonModel = new WarrantBook(); 
      model.CopyProperties(jsonModel); 
      return jsonModel; 
     } 
     return new WarrantBook(); 
    }