Add an attribute to an element in an existing XML using Xquery

Question

I need to add an attribute to an element of my response XML using XQuery. Take the below XML as input,

<xyz:RootNode xmlns:abc="url1" xmlns:xyz="url2">
  <abc:OtherNodes/>
  <abc:messageHeader att1="val1" att2="val2">
       <abc:childNodes/>  
  </abc:messageHeader>
  <abc:OtherNodes/>
</xyz:RootNode>

Need an Xquery that add one more attribute newAtt with value newVal and give the result as,

<xyz:RootNode xmlns:abc="url1" xmlns:xyz="url2">
   <abc:OtherNodes/>
   <abc:messageHeader att1="val1" att2="val2" newAtt="newVal">
       <abc:childNodes/>  
  </abc:messageHeader>
  <abc:OtherNodes>
</xyz:RootNode>

Each time the number of attributes of message header may change. So the query should add a new attribute along with all the existing attributes and return the whole document.

Answer 1

Try the following:

xquery version "3.0";

module namespace foo="http://exist-db.org/apps/ns/foo";

declare function foo:process-node($node as node()?, $model as map()) {
    if ($node) then 
    typeswitch($node) 
        case text() return $node
        case element(messageHeader) return foo:messageHeader($node, $model)
        default return element { $node/name() } 
                               { $node/@*, foo:recurse($node, $model) }

    else () 
};

declare function foo:recurse($node as node()?, $model as map()) as item()* {
    if ($node) 
    then 
        for $cnode in $node/node() 
        return foo:process-node($cnode, $model) 
    else ()
};

declare function foo:messageHeader($node as node(), $model as map()) {
element { $node/name() } 
        { $node/@*, 
          attribute { 'newAtt' } { 'newVal' },
          foo:recurse($node, $model)
        }
};

You then call foo:process-node on the RootNode