Question

如何在下面的DoIt函数中获取查询中的一个新属性的值？

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

匿名类型不会被称为匿名类型。所以：

定义一个带有名称的类型（另外6行代码）：

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

现在将GetData签名修改为（0行代码）：

public IEnumerable<Foo> GetData()

你的LINQ查询（3个额外的字符，或者如果你选择更有意义的名字，还有几个字符）：

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 2

您将返回一个匿名类型（通过select new {}），该类型仅在本地范围内有效。您需要创建一个具体类型并从函数而不是对象返回它。

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 3

好吧，DoIt不知道result有一个名为ShortName的属性，因为它的类型为object。您可以创建一个包含结果，使用反射或使用dynamic的具体类。请注意，无论哪种方式，GetData实际上都返回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 4

你不能不使用反射。由于它是匿名类型，因此您无法在DoIt()方法中转换它，因为在编译时不知道类型名称。

Answer 5

这给了我所需要的东西：

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];
}

从LINQ查询中获取值

5 个答案: