How to check the uniqueness of an attribute in an XML file

Question

If I have an XML file and I want to check the uniqueness of the attribute id of each element like the following document:

<classes columns="id,name,short,classroomids,teacherid,grade,customfield1">
  <class id="0ini" name="Initial Class" short="Init" teacherid="" classroomids="" grade="" customfield1="0"/>
  <class id="*2" name="A1" short="A1" teacherid="" classroomids="" grade="" customfield1="30"/>
  <class id="*3" name="A2" short="A2" teacherid="" classroomids="" grade="" customfield1=""/>
</classes>

I want to check that the id attribute is unique.

score 3 · Answer 1 · edited Jan 08 '12 at 13:27

3

Assuming you can't add it to the schema, you could use LINQ to XML for that:

var allIds = doc.Descendants()
                .Select(x => x.Attribute("id"))
                .Where(x => x != null)
                .Select(x => x.Value)
                .ToList();
var allDistinct = allIds.Count == allIds.Distinct().Count();

edited Jan 08 '12 at 13:27

svick

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answered Jan 08 '12 at 12:10

Jon Skeet

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hmmm,thanks a lot .is this for one element or for all elements: the xml file like this : – Anyname Donotcare Jan 08 '12 at 12:13
1

@just_name: It's the whole document - that's what the Descendants call does. – Jon Skeet Jan 08 '12 at 13:20

score 1 · Answer 2 · edited May 23 '17 at 11:55

1

In code or what? You could always add XML Scheme or DTD and check validity (you can define attr to be unique).

i.e. write XMLScheme or DTD (DTD is simpler, but less flexible), to define structure of your XML. Define there that attribute id of tag class is unique (is ID in DTD). In code, check if given XML is valid against XML Sheme / DTD

Tuts for XML Schemas Unique and DTDs ID:

XML XSD Schema - Enforce Unique Attribute Values in Schema

http://www.featureblend.com/dtd-unique-attribute.html

and search for validating xml in code.

edited May 23 '17 at 11:55

Community

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answered Jan 08 '12 at 12:09

Adam Jurczyk

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Could U give me an example or link to what u want to say? – Anyname Donotcare Jan 08 '12 at 12:10
see edit. BTW, `colums` in `classes` seems excessive and wrong to me. Defining what attributes tags have is document structure, not data - it should be in schema/dtd, not in parent element. – Adam Jurczyk Jan 08 '12 at 12:30

score 1 · Accepted Answer · edited Jan 08 '12 at 13:26

1

You can use a HashSet to check for uniqueness.

var set = new HashSet<string>();
foreach(var id in doc.Descendants()
                 .Select(a => a.Attribute("id").Value))
  if(!set.Add(id))
    throw new Exception("Not Unique");

edited Jan 08 '12 at 13:26

svick

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answered Jan 08 '12 at 12:11

Magnus

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score 1 · Answer 4 · answered Jan 08 '12 at 12:26

var data = XElement.Parse (@"
<classes columns='id,name,short,classroomids,teacherid,grade,customfield1'>
   <class id='0ini' name='Initial Class' short='Init' teacherid='' classroomids='' grade='' customfield1='0'/>
   <class id='*2' name='A1' short='A1' teacherid='' classroomids='' grade='' customfield1='30'/>
   <class id='*3' name='A2' short='A2' teacherid='' classroomids='' grade='' customfield1=''/>
</classes>");       

bool containsDuplicates = data.Descendants().GroupBy(desc=>desc.Attribute("id").Value).Any(grp=>grp.Count()>1);

score 1 · Answer 5 · answered Jan 08 '12 at 13:00

This XPath returns a boolean value indicating whether or not there are repeated @id values:

boolean(//*/@id[.=following::*/@id])

Applied with the XPathEvaluate method:

XDocument d = XDocument.Parse(xml);
bool hasDuplicateId = (bool)d.XPathEvaluate("boolean(//*/@id[.=following::*/@id])");

How to check the uniqueness of an attribute in an XML file

5 Answers5