How to generate empty tag using XMLForest

Question

Hi,
I am creating an XML document using XMLAgg, XMLForest and XMlElement functions.
At some point I have an XMLForest embedded in the other XMLForest
XMLForest( e.indicator as "col1",
           e.participant_id as "col2",
  XMLForest( tableAlias.col11 as "address1",
             tableAlias.col12 as "address2",            
           ) as "items",
)           and within the last one I have some expressions which are empty, so the XML tags are not generated, however I have to have an empty tags:
<address2></address2>I tried to replace an expression using "NVL" or "DECODE", but the results were the same.
I also tried to replace an embedded XMLForest with an XMLElement :
XMLForest( e.indicator as "col1",
           e.participant_id as "col2",
  *XMLElement("items"*
             *XMLElement("address1"),*
             *XMLElement("address2")*
           *) as "items",*)           however it created 2 <items> tags :
    <items>
         <items>
            <address1>value</address1>
            <address2></address2>
         </items>
     </items> I am working with Oracle 11.2.0 db.
Is there any way to generate an empty tag when using XMLForest function?
thank you in advance.
Edited by: user624274 on Apr 3, 2013 8:52 AM
Edited by: user624274 on Apr 3, 2013 8:53 AM

Answer 1

Hello Odie_63.
Your argument is valid, but it does not mean the solution I provided is bad.
If you are concerned about the size of the result, it is simple, you can use like:
REPLACE(XMLForest( NVL(e.indicator, '#NULLValue#') as "col1",  NVL(e.participant_id, '#NULLValue#') as "col2").getClobVal(), '#NULLValue#', '')
According to Oracle documentation, REPLACE is smart and will return a CLOB (not a varchar2) because it changes the type of return according to the type of the first parameter. So you will not have issues with size.
I believe the first question was related to use the final result to record to a table or send to another system (to use as integration). If it will be used just in a select field, it does not matter if it is not there or if it is there as NULL, the select of the field will always return ''.
Other hint, I never use xmltype to store on database, because it is not compatible with other databases or integration tools. I use CLOB because it is the natural serialization of the object and I can convert and work with it inside and outside Oracle.
But that is up to the architect and/or developer. If the system is running only on Oracle and there is no integration, maybe xmltype will save a lot of time in conversions.
Regards.
Rodolpho