c#连接DefaultIfEmpty文件使用Linq DefaultIfEmpty()生成重复

Question

我试图在两个XML文档上完成一个leftOuterJoin，但是我目前使用的方式似乎是从fileone返回一些奇怪的重复部分(在下面的代码中解释)。我试过很多种方法，但都想不出怎么做。有人能帮我解决这个问题吗？事先非常感谢！

fileone：

<fileone>

    <Book BookID="dog"> Dog </Book>

    <Book BookID="cat"> Cat </Book>

</fileone>

文件二：

<filetwo>

       <Edition BID="cat" OrderID="100"> about cat</Edition>

       <Edition BID="cat" OrderID="200">more about cat</Edition>

</RightSeq>

我要找的是(bookID=BID上的左外部连接)：

<item>
   <Book BookID="cat"> Dog </Book>
</item>
<item>
    <Book BookID="cat"> Cat </Book>
    <Edition BID="cat" OrderID="100"> about cat</Edition>
</item>
<item>
    <Book BookID="cat"> Cat </Book>
    <Edition BID="cat" OrderID="200"> more cat</Edition>
</item>

我的(错误)代码：

      var result = from a in fileone.Descendants()
      join b in secondxdoc.Descendants()
     on (string)a.Attribute("BookID") equal (string)b.Attribute("BID") into inners
      from ele in inners.DefaultIfEmpty()

      select new XElement("item", new XElement(a), ele == null ? null : new XElement(ele));
        var output = new XElement("LeftOuterJoin", result);         
    }

目前的错误结果：

<item>
   <fileone>  
       <Book BookID="dog"> Dog </Book> // this entire <fileone> bit is unwanted
       <Book BookID="cat"> Cat </Book>  //I don't know what I've done wrong
   </fileone> 
</item>
    <item>
   <Book BookID="cat"> Dog </Book>
</item>
<item>
    <Book BookID="cat"> Cat </Book>
    <Edition BID="cat" OrderID="100"> about cat</Edition>
</item>
<item>
    <Book BookID="cat"> Cat </Book>
    <Edition BID="cat" OrderID="200"> more cat</Edition>
</item>  

Answer 1

我没有使用传统的linq就得到了结果。在文件2中没有匹配项的情况下，联接不会给出结果。

​

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 input1 =
               "<fileone>" +
                   "<Book BookID=\"dog\"> Dog </Book>" +
                   "<Book BookID=\"cat\"> Cat </Book>" +
               "</fileone>";
            XDocument fileone = XDocument.Parse(input1);

            string input2 =
               "<filetwo>" +
                      "<Edition BID=\"cat\" OrderID=\"100\"> about cat</Edition>" +
                      "<Edition BID=\"cat\" OrderID=\"200\">more about cat</Edition>" +
               "</filetwo>";
            XDocument secondxdoc = XDocument.Parse(input2);

            //<item>
            //   <Book BookID="cat"> Dog </Book>
            //</item>
            //<item>
            //    <Book BookID="cat"> Cat </Book>
            //    <Edition BID="cat" OrderID="100"> about cat</Edition>
            //</item>
            //<item>
            //    <Book BookID="cat"> Cat </Book>
            //    <Edition BID="cat" OrderID="200"> more cat</Edition>
            //</item>
            XElement output = new XElement("Root");
            foreach (XElement item in fileone.Descendants("Book"))
            {
                string bookId = item.Attribute("BookID").Value;
                List<XElement> bookTwoItems = secondxdoc.Descendants("Edition").Where(x => x.Attribute("BID").Value == bookId).ToList();
                if (bookTwoItems.Count  == 0)
                {
                    XElement newItem = new XElement("item");
                    output.Add(newItem);
                    newItem.Add(item);
                }
                else
                {
                    foreach (XElement bookTwoItem in bookTwoItems)
                    {
                        XElement newItem = new XElement("item");
                        output.Add(newItem);
                        newItem.Add(item);
                        newItem.Add(bookTwoItem);
                    }
                }
                
            }
        
        }
    }
}
​

​

让它与左外接一起工作

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 input1 =
               "<fileone>" +
                   "<Book BookID=\"dog\"> Dog </Book>" +
                   "<Book BookID=\"cat\"> Cat </Book>" +
               "</fileone>";
            XDocument fileone = XDocument.Parse(input1);

            string input2 =
               "<filetwo>" +
                      "<Edition BID=\"cat\" OrderID=\"100\"> about cat</Edition>" +
                      "<Edition BID=\"cat\" OrderID=\"200\">more about cat</Edition>" +
               "</filetwo>";
            XDocument secondxdoc = XDocument.Parse(input2);

            //<item>
            //   <Book BookID="cat"> Dog </Book>
            //</item>
            //<item>
            //    <Book BookID="cat"> Cat </Book>
            //    <Edition BID="cat" OrderID="100"> about cat</Edition>
            //</item>
            //<item>
            //    <Book BookID="cat"> Cat </Book>
            //    <Edition BID="cat" OrderID="200"> more cat</Edition>
            //</item>
            var results = (from one in fileone.Descendants("Book")
                           join two in secondxdoc.Descendants("Edition") on one.Attribute("BookID").Value equals two.Attribute("BID").Value into inners
                           from two in inners.DefaultIfEmpty()
                           select new { fileone = one, filetwo = two == null ? null : two }).ToList(); 
            XElement output = new XElement("Root");
            foreach (var item in results)
            {
                XElement newItem = new XElement("item");
                output.Add(newItem);
                newItem.Add(item.fileone);
                if (item.filetwo  != null)
                {
                        newItem.Add(item.filetwo);
                }

            }

        }
    }
}
​

或者这种方法

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 input1 =
               "<fileone>" +
                   "<Book BookID=\"dog\"> Dog </Book>" +
                   "<Book BookID=\"cat\"> Cat </Book>" +
               "</fileone>";
            XDocument fileone = XDocument.Parse(input1);

            string input2 =
               "<filetwo>" +
                      "<Edition BID=\"cat\" OrderID=\"100\"> about cat</Edition>" +
                      "<Edition BID=\"cat\" OrderID=\"200\">more about cat</Edition>" +
               "</filetwo>";
            XDocument secondxdoc = XDocument.Parse(input2);

            //<item>
            //   <Book BookID="cat"> Dog </Book>
            //</item>
            //<item>
            //    <Book BookID="cat"> Cat </Book>
            //    <Edition BID="cat" OrderID="100"> about cat</Edition>
            //</item>
            //<item>
            //    <Book BookID="cat"> Cat </Book>
            //    <Edition BID="cat" OrderID="200"> more cat</Edition>
            //</item>
            XElement output = new XElement("Root");
            var results = (from one in fileone.Descendants("Book")
                           join two in secondxdoc.Descendants("Edition") on one.Attribute("BookID").Value equals two.Attribute("BID").Value into inners
                           from two in inners.DefaultIfEmpty()
                           select new { fileone = one, filetwo = two == null ? null : two })
                           .Select(x => x.filetwo == null ? new XElement("item", x.fileone) : new XElement("item", new object[] { x.fileone, x.filetwo }));
            foreach (var item in results)
            {
                output.Add(item);
            }
        }
    }
}
​