Inserting a child node when list is empty (XForms) - insert

Question

My problem is the following :
I usually have those data:
<structures>
<structure id="10">
<code>XXX</code>
</structure>
</structures>
so the table I display (single columns : code) is ok.
But in some cases, the data is the result a a query with no content, so the data is:
<structures/>
resulting in my table not displaying + error.
I am trying to insert, in the case of an empty instance, a single node so that the data would look like:
<structures>
<structure id="0"/>
</structures>
I am trying something like that :
<xforms:action ev:event="xforms-submit-done">
<xforms:insert if="0 = count(instance('{./instance-name}')/root/node())" context="instance('{./instance-name}')/root/node()" origin="xforms:element('structure', '')" />
</xforms:action>
but no node inserted when I look at the data in the inspector in the page.
Any obvious thing I am doing wrong?

Answer 1

There seems to be erros in your XPath if and context expressions:
if="0 = count(instance('{./instance-name}')/root/node())"
context="instance('{./instance-name}')/root/node()"
You are a using curly brackets { and }, I assume to have the behavior of attribute value templates (AVTs). But the if and context expressions are already XPath expressions, so you cannot use AVTs in them. Try instead:
if="0 = count(instance(instance-name)/root/node())"
context="instance(instance-name)/root/node()"
Also, the instance-name path is relative to something which might not be clear when reading or writing the expression. I would suggest using an absolute path for example instance('foo')/instance-name to make things clearer.
You don't provide the structure of the other instances, so I can tell for sure, but you'll expression above suppose that they have the form:
<xf:instance id="foo">
<some-root-element>
<root>
<structure/>
</root>
<some-root-element>
</xf:instance>
I don't know if that's what you intend.
Finally, you could replace count(something) = 0, with empty(something).