XQuery

Clarity

You can increase the clarity of your queries by improving the layout of the query, making appropriate use of names, and using comments liberally. In addition to the recommendations in this chapter, you can go to http://www.xqdoc.org/xquery-style.html for some more detailed XQuery style conventions.

Improving the Layout

To make the structure of a query more obvious, you should make appropriate use of whitespace and parentheses. Whitespace (line breaks, spaces, and tabs) is allowed anywhere between keywords to make it more readable.

It is helpful to split longer FLWOR and conditional expressions into multiple lines and indent each clause to line up, as shown in Example 15-1. FLWORs embedded within FLWORs should be further indented. When constructing XML results, you should indent the element constructors just as you would indent the elements in an XML document.

Example 15-1. Making use of whitespace

Less clear query
for $product in doc("catalog.xml")//product return
<product><number>{$product/number}</number>
<price>{for $price in doc("prices.xml")//prod
where $product/number = $price/@num
return $price/price}</price>
</product>
More clear query
for    $product in doc("catalog.xml")//product
return <product>
         <number>{$product/number}</number>
         <price>{for    $price in doc("prices.xml")//prod
                 return $price/price}</price>
       </product>

Parentheses can be used around most expressions to group them together. If the beginning and end of an expression are not obvious, parentheses are highly recommended. ...