On 21/09/10 12:05, Jody Garnett wrote:
I understand the problem with using null to represent two cases; can
you check the filter and xpath specifications to see how they handle
this problem? Do they produce an error; or return an empty result? The
answer may inform what we do here; perhaps they have thought of a good
way to be clear?
It seems to me that the filter specification doesn't mention the case of
non-existent properties at all. It only mentions the case of a null value
The *<PropertyIsNull> *element encodes an operator that checks to see if
the value of its content is NULL. A NULL is equivalent to no value
present. The value 0 is a valid value and is not considered NULL.
'The value of its content' implies to me that there is still a property,
but this is open for interpretation of course.
X-Path will return an 'empty list' when an element doesn't exist. There
isn't really such a thing as null values in xpath as such.
If you have a builder object for your mapping file could you make use
of additional information to prevent an invalid mapping file being
produced? Allow it to throw exceptions of the filters being passed in
do not match the data they are to run on?
Hmmm mappings are expressions that can contain functions, operators,
etc... and properties can be evaluated with several property accessors.
I do no see how the property names can be tested without recursively
going through the expression tree and trying the several property
accessors - basically evaluating it.
--
*Niels Charlier*
Software Engineer
CSIRO Earth Science and Resource Engineering
Phone: +61 8 6436 8914
Australian Resources Research Centre
26 Dick Perry Avenue, Kensington WA 6151
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