在C＃中使用LINQ从XML获取节点

Question

My code is as follows:

XDocument xmlDoc = XDocument.Load("myXML.xml");

        var data = from items in xmlDoc.Root.Elements("category")
                   where items.Attribute("value").Value == "idxCategoryPlatformEngine"
                   select new
                   {
                       attribute = items.Element("attributes").Element("attribute").Element("name").Value,
                       trigger = items.Element("attributes").Element("attribute").Element("trigger").Value,
                       value = items.Element("attributes").Element("attribute").Element("value").Value,
                       minutes = items.Element("attributes").Element("attribute").Element("minutes").Value
                   };

The XML I have is as follows:

<?xml version="1.0" encoding="utf-8"?>
<GMS>
    <category value="idxCategoryPlatformEngine">
        <attributes>
            <attribute>
                <name>CheckpointFileCorruptionAlarm.InAlarm</name>
                <trigger>EQ</trigger>
                 <value>TRUE</value>
                 <minutes>0</minutes>
            </attribute>
            <attribute>
                 <name>CPULoad</name>
                <trigger>GT</trigger>
                <value>60</value>
                <minutes>5</minutes>
            </attribute>
            <attribute>
                <name>Engine.Historian.InStoreForward</name>
                <trigger>EQ</trigger>
                <value>TRUE</value>
                <minutes>0</minutes>
            </attribute>
        </attributes>
    </category>
    <category value="idxCategoryApplicationEngine">
        <attributes>
            <attribute>
                <name>CheckpointFileCorruptionAlarm.InAlarm</name>
                <trigger>EQ</trigger>
                 <value>TRUE</value>
                 <minutes>0</minutes>
            </attribute>
            <attribute>
                 <name>CPULoad</name>
                <trigger>GT</trigger>
                <value>60</value>
                <minutes>5</minutes>
            </attribute>
            <attribute>
                <name>Engine.Historian.InStoreForward</name>
                <trigger>EQ</trigger>
                <value>TRUE</value>
                <minutes>0</minutes>
            </attribute>
        </attributes>
    </category>
</GMS>

Now when I run the code it does perform the query however it only returns the first attribute where I actually want all attributes.

I'd appreciate any help on this as it is driving me crazy, each change I make to try fix this only results in more issues!

Answer 1

The problem is that by down selecting to the attribute element inside the select statement, you're only executing it once. In other words, you're passing in a collection to select, and the select is running statements like items.Element("attributes").Element("attribute").Element("name").Value to get a single value and a single anonymous object. It should look more like this (which works):

var data2 = doc.Root.Elements("category")
    .Where(x => x.Attribute("value").Value == "idxCategoryPlatformEngine")
    .Elements("attributes")
    .Elements("attribute")
    .Select(x => new
    {
        attribute = x.Element("name").Value,
        trigger = x.Element("trigger").Value,
        value = x.Element("value").Value,
        minutes = x.Element("minutes").Value
    });

I'm more comfortable with the extension syntax for Linq, but this can easily be converted to the other syntax.

Answer 2

You should add one additional select into select new { } , now you are only returning values of the first attribute :

var data = from item in xmlDoc.Root.Elements("category")
           where item.Attribute("value").Value == "idxCategoryPlatformEngine"
           select new
               {
                   category = item.Attribute("value").Value,
                   attributes = from attr in item.Element("attributes")
                                select new {
                                   attribute = attr.Element("name").Value,
                                   trigger = attr.Element("trigger").Value,
                                   ...
                                }
               };

Answer 3

First you need to get at the Attributes element and then iterate all the Attribute elements under it.

You can do it like this:

  XDocument xmlDoc = XDocument.Load("myXML.xml");

  var data = (from items in xmlDoc.Root.Elements("category")
              where items.Attribute("value").Value == "idxCategoryPlatformEngine"
              select new {attrs  = items.Element("attributes")})
              .SelectMany(a => a.attrs.Elements("attribute"))
              .Select(item => new {
                       attribute = item.Element("name").Value,
                       trigger = item.Element("trigger").Value,
                       value = item.Element("value").Value,
                       minutes = item.Element("minutes").Value
              });