trailing block elements must have an id attribute

A couple of weeks back some colleagues working on a POC came across this runtime error when invoking a web service through a generated web service proxy client:

trailing block elements must have an id attribute

This exception was being thrown within the web service proxy client when parsing the response from the web service. Using HttpAnalyzer in JDeveloper (versions 10.1.3.1 & 10.1.3.2 were used) we could see that the request was being sent and a response was being received, so clearly nothing wrong with the web service being invoked. Or so we thought…

It turned out that the published WSDL & XSD and the web service implementation were not matching. The XSD for an element in the response said that Address had a maxOccurs=”1″ however, the web service implementation was returning multiple Address elements. The web service proxy client is generated from the WSDL & XSD so it is only expecting one Address element in the response stream, hence the error at runtime.

We had to double check which was correct, and a quick check through documentation showed that the schema had not been updated when the object model had changed. Once that was determined, it was straight forward to correct the schema entry, maxOccurs=”unbounded”, and regenerate the web service proxy client.

So, if you get this obscure ‘trailing block elements must have an id attribute’ error message at runtime double check that the published interfaces (WSDL & XSD) match the implementation.