How to create an index for an attribute in exist-db

Question

I am updating an XML file in an exist-db collection and I have to check if and id is present to decide if I have to replace or insert something in my document.

I noticed that as the file grows the query execution time worsens significantly and I decided to add an index for my file.

I understand that I have to do that in the conf.xml of my exist-db as it is shown in this example:

<!-- Range indexes -->
<create qname="title" type="xs:string"/>
<create qname="author" type="xs:string"/>
<create qname="year" type="xs:integer"/>
<!-- "old" context-dependant configuration using the path attribute: -->
<create path="//booktitle" type="xs:string"/>

I want to add an index for the attribute id in an xml like the following:

<server>
  <formal>
    <lastimage>
      <harvested>
        <coverages>
          <coverage active="true" id="EUDEM">
          ...
          </coverage>
        </coverages>
      </harvested>
    </lastimage>
  </formal>
</server>

I don't think that adding

<create qname="id" type="xs:string"/>

is enough.

What is the right way of adding and index in exist-db for this attribute?

Answer 1

You're close! Just add @ to the beginning of the qname attribute:

 <create qname="@id" type="xs:string"/>

The relevant section of the documentation is Configuration by path vs. configuration by qname:

Attributes are specified by @attributeName, so if the attribute is called "attrib1", one uses @attrib1 in the index specification.