c# sort by elements or attribute with one method

Question

I need to sort xml documents sometimes by attributes, sometimes by elements, depending on what type of documents comes in. How can I use one sortBy method in c# to solove this problem? Many thanks for your help! For example my sorting key is "bookID"element or attribute, and the xml files are:

 <bookstore>
  <book>
    <bookID>100</bookID>
    <name> The cat in the hat <name>
  </book>
  <book>
    <bookID>90</bookID>
    <name> another book <name>
  </book>
  <book>
    <bookID>103</bookID>
    <name> a new book <name>
  </book>
  </bookstore>

or sometimes the xml comes in the below format:

<bookstore>
  <book bookID="100">The cat in the hat</book> 
  <book bookID="90">another book</book> 
  <book bookID="103"> a new book</book> 
</bookstore>

Anthony Pegram · Accepted Answer · 2021-12-22 04:17:20Z

1

You will need to handle both possibilities in your query, assuming you are using Linq-to-XML for this. You might utilize the let keyword, but the basic idea is to check for either the attribute or the element for null and use the appropriate value.

var books = from book in document.Element("bookstore").Elements("book")
            let bookId = book.Attribute("bookID") != null 
                ? book.Attribute("bookID").Value 
                : book.Element("bookID").Value
            orderby int.Parse(bookId)
            select book; // project properties of book as needed

edited Dec 22, 2021 at 4:17

answered Aug 3, 2015 at 1:51

Anthony Pegram

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2 Comments

user4046073 Over a year ago

Thanks for the reply! somehow bookId = book.Attribute("bookID") != null soes not work for me. It always returns true whether there is attribute or not..

Anthony Pegram Over a year ago

Is "bookID" of a differing case in your actual XML? I took both your XML snippets (and had to clean one up, your "name" elements are not properly closed) and the code executed successfully on each.

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