GroupBy Linq 结果上的多个 Groupby

Question

假设我有两个班级

class Foo
{
 List<Bar> Bars{get;set;} 
}

class Bar
{
  string Name{get;set;}
  string Value{get;set;}
}

我有一个这样的查询

var resultsGroupedByState=Foos.GroupBy(x=>x.Bars.First(c=>c.Name=="state").Value);

这将返回按状态分组的结果，此外，用户可以定义按字段分组的层次结构，例如

1. 按州分组
2. 按县分组
3. groupBy City 等等

我要做多少级 groupBy，我不知道。我必须先在层次结构中定义一个 groupby，然后根据层次结构中的第二个值对第一个 groupby 的结果进行 groupby，然后继续。

最后，我必须像这样从该数据生成一个 xml。

<State value="anyState">
   <County value="anyCounty">
       <City value="anyCity">
          ..........
        </City>
    </County>
 </State>

Answer 1

基本上你需要生成 XML。一种解决方案是递归地执行GroupBy 并直接创建XMLDocument。

这是一个可以做到这一点的辅助类。

public class XmlGenerator
{
    private XmlDocument _document;
    private List<string> _fields;
    private int index = 0;

    public XmlGenerator(List<string> fields)
    {
        _fields = fields;
    }

    public void GenerateXML(IEnumerable<Foo> lookupData, XmlElement root, string field)
    {
        var fieldGrouping = lookupData.GroupBy(v => v.Bars.First(x => x.Name == field).Value);
        foreach (var grouping in fieldGrouping)
        {
            var element = _document.CreateElement(field);
            var attrib = _document.CreateAttribute("value");
            attrib.InnerText = grouping.Key;

            element.Attributes.Append(attrib);
            root.AppendChild(element);

            // If that is last field. No need to do any grouping.
            if (index < _fields.Count - 1)
            {
                // After each nested call update the nested level.
                // If GenerateXML do another that will be upon next nested level
                index += 1;
                GenerateXML(grouping, element, _fields[index]);
                index -= 1;
                // Make sure to change back nested level index otherwise that will not works if you have multiple groups.
            }
        }
    }

    public string GenerateXML(IEnumerable<Foo> lookupData)
    {
        _document = new XmlDocument();
        var root = _document.CreateElement("Root");
        _document.AppendChild(root);
        index = 0;

        GenerateXML(lookupData, root, _fields[index]);

        return _document.OuterXml;
    }
}

实际上我在这里所做的是，我将所有字段列表存储在List<string>. 中，并编写了一个按特定字段分组的辅助方法。每次传递时，我都会传递需要分组的方法数据和要分组的字段名称。

希望如此，这可以解决您的问题。

Answer 2

您不需要 GroupBy。试试这个

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Xml;
using System.Xml.Linq;

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
           string xml =
               "<Root>" +
                    "<State value=\"AState\">" +
                       "<County value=\"ACounty\">" +
                           "<City value=\"ACity\"/>" +
                           "<City value=\"BCity\"/>" +
                           "<City value=\"CCity\"/>" +
                        "</County>" +
                       "<County value=\"BCounty\">" +
                           "<City value=\"ACity\"/>" +
                           "<City value=\"BCity\"/>" +
                           "<City value=\"CCity\"/>" +
                        "</County>" +
                       "<County value=\"CCounty\">" +
                           "<City value=\"ACity\"/>" +
                           "<City value=\"BCity\"/>" +
                           "<City value=\"CCity\"/>" +
                        "</County>" +
                     "</State>" +
                    "<State value=\"BState\">" +
                       "<County value=\"ACounty\">" +
                           "<City value=\"ACity\"/>" +
                           "<City value=\"BCity\"/>" +
                           "<City value=\"CCity\"/>" +
                        "</County>" +
                       "<County value=\"BCounty\">" +
                           "<City value=\"ACity\"/>" +
                           "<City value=\"BCity\"/>" +
                           "<City value=\"CCity\"/>" +
                        "</County>" +
                       "<County value=\"CCounty\">" +
                           "<City value=\"ACity\"/>" +
                           "<City value=\"BCity\"/>" +
                           "<City value=\"CCity\"/>" +
                        "</County>" +
                     "</State>" +
                     "<State value=\"CState\">" +
                       "<County value=\"ACounty\">" +
                           "<City value=\"ACity\"/>" +
                           "<City value=\"BCity\"/>" +
                           "<City value=\"CCity\"/>" +
                        "</County>" +
                       "<County value=\"BCounty\">" +
                           "<City value=\"ACity\"/>" +
                           "<City value=\"BCity\"/>" +
                           "<City value=\"CCity\"/>" +
                        "</County>" +
                       "<County value=\"CCounty\">" +
                           "<City value=\"ACity\"/>" +
                           "<City value=\"BCity\"/>" +
                           "<City value=\"CCity\"/>" +
                        "</County>" +
                     "</State>" +
                    "</Root>";

           XElement root = XElement.Parse(xml);

           List<Foo> foos = Helper(root); 

        }
        public static List<Foo> Helper(XElement element)
        {
            if (element.HasElements)
            {
                string tagName = ((XElement)element.FirstNode).Name.LocalName;

                List<Foo> children = element.Elements(tagName).Select(x => new Foo()
                {
                    Name = tagName,
                    Value = (string)x.Attribute("value"),
                    foos = Helper(x)
                }).ToList();


                return children;
            }
            else
            {
                return null;
            }
        }
    }
    public class Foo
    {
        public string Name { get; set; }
        public string Value { get; set; }

        public List<Foo> foos { get; set; }
    }

}