從LINQ查詢中獲取值

Question

如何在下面的DoIt函數中查詢其中一個新屬性的值？

public object GetData() 
{ 
     var table = GetDataTable(); 
     var view = table.DefaultView; 
     //..... more code 
     var query = from row in view.ToTable().AsEnumerable() 
        group row by row.Field<string>("ShortName") into grouping 
        select new 
         { 
          ShortName = grouping.Key, 
          SCount = grouping.Sum(count => count.Field<int>("ProfCount")), 
          DisplayText = string.Empty 
         }; 
     return query; 
} 

// this code doesn't work 
public void DoIt() 
{ 
    var result = GetData(); 
    string shortName = result.ShortName; 
} 

謝謝！

Answer 1

你返回一個匿名類型（通過選擇新的{}），這是隻有在局部範圍內有效。你需要創建一個具體類型並從你的函數而不是對象中返回。

public SomeClass GetData() 
{ 
     var table = GetDataTable(); 
     var view = table.DefaultView; 
     //..... more code 
     var query = from row in view.ToTable().AsEnumerable() 
        group row by row.Field<string>("ShortName") into grouping 
        select new SomeClass 
         { 
          ShortName = grouping.Key, 
          SCount = grouping.Sum(count => count.Field<int>("ProfCount")), 
          DisplayText = string.Empty 
         }; 
     return query; 
} 

// this code doesn't work 
public void DoIt() 
{ 
    var result = GetData(); 
    string shortName = result.ShortName; 
} 

public class SomeClass 
{ 
    public string ShortName { get; set; } 
    public int SCount { get; set; } 
    public string DisplayText { get; set; } 
} 

Answer 2

匿名類型不會被稱爲匿名類型。所以：

定義類型與名稱（代碼6個其他行）：

public class Foo 
{ 
    public string ShortName { get; set; } 
    public int SCount { get; set; } 
    public string DisplayText { get; set; } 
} 

現在修改GetData簽名（代碼0其他行）：

public IEnumerable<Foo> GetData() 

和你LINQ查詢到（3個附加字符，或者如果您選擇更有意義的名稱，則更多）：

var query = 
    from row in view.ToTable().AsEnumerable() 
    group row by row.Field<string>("ShortName") into grouping 
    select new Foo 
    { 
     ShortName = grouping.Key, 
     SCount = grouping.Sum(count => count.Field<int>("ProfCount")), 
     DisplayText = string.Empty 
    }; 

Answer 3

你不能沒有使用反射。由於它是匿名類型，因此無法在DoIt()方法中強制轉換爲類型名稱，因爲在編譯時不知道類型名稱。

Answer 4

嗯，DoIt不知道result有一個名爲ShortName的屬性，因爲它的類型爲object。您可以創建一個具體的類來保存結果，使用反射或使用dynamic。請注意，無論哪種方式，GetData確實會返回IEnumerable<T>，其中T目前是匿名類型。

使用具體類：

public class Foo { 
    public string ShortName { get; set; } 
    public int SCount { get; set; } 
    public string DisplayText { get; set; } 
} 

public IEnumerable<Foo> GetData() { 
    var table = GetDataTable(); 
    var view = table.DefaultView; 
    //..... more code 
    var query = from row in view.ToTable().AsEnumerable() 
       group row by row.Field<string>("ShortName") into grouping 
       select new Foo 
        { 
         ShortName = grouping.Key, 
         SCount = grouping.Sum(count => count.Field<int>("ProfCount")), 
         DisplayText = string.Empty 
        }; 
    return query; 
} 

public void DoIt() { 
    var result = GetData(); 
    foreach(var item in result) { 
     Console.WriteLine(item.ShortName); 
    } 
} 

使用反射：

public IEnumerable GetData() { 
    var table = GetDataTable(); 
    var view = table.DefaultView; 
    //..... more code 
    var query = from row in view.ToTable().AsEnumerable() 
       group row by row.Field<string>("ShortName") into grouping 
       select new Foo 
        { 
         ShortName = grouping.Key, 
         SCount = grouping.Sum(count => count.Field<int>("ProfCount")), 
         DisplayText = string.Empty 
        }; 
    return query; 
} 

public void DoIt() { 
    var result = GetData(); 
    PropertyInfo property = result.First().GetType().GetProperty("ShortName"); 
    foreach(var item in result) { 
     string shortName = property.GetValue(item, null); 
     Console.WriteLine(shortName); 
    } 
} 

Answer 5

這給了我什麼，我需要：

public object GetData() 
{ 
     var table = GetDataTable(); 
     var view = table.DefaultView; 
     //..... more code 
      var query = from row in view.ToTable().AsEnumerable() 
        group row by row.Field<string>("ShortName") into grouping 
        select new Object[] 
         { 
          grouping.Key, 
          grouping.Sum(count => count.Field<int>("ProfCount")), 
          string.Empty 
         }; 
      return query; 
} 


public void DoIt() 
{ 
    // Note: Pretend that GetData returned only one result 
    object[] result = GetData() as object[]; 
    var shortName = result[0]; 
}