从LINQ查询中获取值

Question

如何在下面的DoIt函数中查询其中一个新属性的值？

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; 
} 

谢谢！

Answer 1

你返回一个匿名类型（通过选择新的{}），这是只有在局部范围内有效。你需要创建一个具体类型并从你的函数而不是对象中返回。

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

匿名类型不会被称为匿名类型。所以：

定义类型与名称（代码6个其他行）：

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

现在修改GetData签名（代码0其他行）：

public IEnumerable<Foo> GetData() 

和你LINQ查询到（3个附加字符，或者如果您选择更有意义的名称，则更多）：

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

你不能没有使用反射。由于它是匿名类型，因此无法在DoIt()方法中强制转换为类型名称，因为在编译时不知道类型名称。

Answer 4

嗯，DoIt不知道result有一个名为ShortName的属性，因为它的类型为object。您可以创建一个具体的类来保存结果，使用反射或使用dynamic。请注意，无论哪种方式，GetData确实会返回IEnumerable<T>，其中T目前是匿名类型。

使用具体类：

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

这给了我什么，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]; 
}