<assign location="..." expr="..."> problem for context with different internal
XML representation
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Key: SCXML-59
URL: https://issues.apache.org/jira/browse/SCXML-59
Project: Commons SCXML
Issue Type: Improvement
Affects Versions: 0.6
Reporter: Ingmar Kliche
We are currently working on a prototype implementation of a ECMAScript context
and evaluator based on Rhino.
It appears that Rhino has its internal context and uses an internal XML
representation different from org.w3c.dom.node. This means we have to convert
every XML Node/Document when it is stored into the context into Rhino's
internal XML representation (e.g. when the datamodel is stored into the
context). This works fine.
The problem occurs with the current implementation of <assign location="..."
expr="...">. Assign uses evalLocation() twice to get two org.w3c.dom.node
objects (one for location and another for expr). Then the implementation of
Assign iterates through the two node structures and stores the expr node under
the location node.
Doing this, Assign manipulates a variable within the context from outside, i.e.
it manipulates the XML data tree without using a set() at the context. To do
this it makes use of object references.
For our context this appears to be a problem. As mentioned earlier we have a
different internal XML representation (i.e. other Java classes than
org.w3c.dom). Therefore our evalLocation() returns a org.w3c.dom.node object
(as required by the context interface) which is a converted copy of the
internal XML object. Assign therefore works on our copies and as it does not
store the result explicitly back into the context we loose it.
I see the current implementation of Assign therefore as a violation of the
context abstraction (because Assign manipulates data within the context from
outside) and propose to change it. I propose to think about a solution which
avoids data convertion (as described above) whereever possible for
evaluators/contexts which use different internal (XML) data representation.
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