XQuery递归函数

Question

I asked similiar to this question before but I'm still not handled this case correctly, firstly I'm saying that I am new to this XQuery language so configure the recursive strategy is really hard for me for now.

XQuery Sample Code to be executed :

declare variable $stuff :=
  <doc>
  <embed-session>
    <session>
          <title>Fred Smith</title>
     <session>
     <title>Ahmet Özcan</title>
     <session>
     <title>Erman Bey</title>
     </session>
     </session>
    </session>
    </embed-session>
  </doc>;

declare function local:change($node as node()) as element()
{
  typeswitch($node)
  case element() return 
    element { fn:node-name($node) } {
      attribute title {data($node/title)},
      $node/session ! local:change(.)
    }
  default return $node
};

local:change($stuff/embed-session/session)

The output of the code : 

<session title="Fred Smith">
  <session title="Ahmet Özcan">
    <session title="Erman Bey"/>
  </session>
</session>

It seems that it fits with my expectations but if I add one more embed session node to my stuff variable for example :

<embed-session>
<session>
<title>Ferhat Bey</title>
</session>
</embed-session>

to my parameter of the function it says that : [XPTY0004] Cannot treat item() sequence as node(): (..., )

The expected output of the code after add the embed-session mentioned below :

<session title="Fred Smith">
  <session title="Ahmet Özcan">
    <session title="Erman Bey"/>
  </session>
</session>

<session title="Ferhat Bey"/>

I know it is sequence but why I couldn't assign sequence to node as parameter ?

Answer 1

It's always a good idea to declare the expected types of your function arguments. I think you are expecting $node to be a node, but in your function call you are supplying a sequence of nodes. element(x) only matches a singleton sequence, so it is not matching when you supply more than one. If you had written "$node as node()" then this simple error would have been caught much more quickly, and we would all have saved a lot of time.