linq to xml-如何基于多字段查询获取XElement

Question

I have this xml file:

<?xml version="1.0" encoding="utf-8"?>
<FieldsDefinitions>
  <FieldsDefinition>
    <Field>DEMOFIELD</Field>
    <Length>15</Length>
    <Label>IIS: </Label>
    <Type>DropDown</Type>
  </FieldsDefinition>
  <FieldsDefinition>
    <Field>IIS</Field>
    <Length>15</Length>
    <Label>IIS: </Label>
    <Type>DropDown</Type>
  </FieldsDefinition>
  <FieldsDefinition>
    <Field>DEMOFIELD</Field>
    <Length>20</Length>
    <Label>Demo Field</Label>
    <Type>Text</Type>
  </FieldsDefinition>
</FieldsDefinitions>

If I want to get all fields with value=DEMOFIELD, I could do something like this:

XDocument xDoc = XDocument.Load("file.xml");
                var x = xDoc.Descendants("Field").Where(elem => elem.Value == "DEMOFIELD");
                foreach(XElement e in x)
                {
                    _log.Debug(e.Name + " = " + e.Value);
                }

But how can I query for field='DEMOFIELD' and label='IIS:'? Do I use a sort of multi-where?

Answer 1

You probably want to step one level up and find all FieldsDefinition elements that match your criteria:

var fieldDefs = doc
    .Descendants("FieldsDefinition")
    .Where(x => (string) x.Element("Field") == "DEMOFIELD" &&
                (string) x.Element("Label") == "IIS: ");

See this fiddle for a working demo.

Answer 2

You should query for FieldsDefinition elements:

var x = from fd in xDoc.Descendants("FieldsDefinition")
        where (string)fd.Element("Field") == "DEMOFIELD"
           && (string)fd.Element("Label") == "IIS: "
        select fd;

NOTE: I would recomend to trim value of label to avoid different number of spaces affect results:

           && ((string)fd.Element("Label")).Trim() == "IIS:"

Also if you are absolutely sure that every FieldsDefinition has both Field and Label element, then you can use Value field directly:

var x = xDoc.Descendants("FieldsDefinition")
            .Where(fd => fd.Element("Field").Value == "DEMOFIELD"
                      && fd.Element("Label").Value.Trim() == "IIS:");