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| IS NOT NULL vs CARDINALITY |
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| crossland |
 Posted: Tue Apr 07, 2009 1:08 am Post subject: IS NOT NULL vs CARDINALITY |
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Master
Joined: 26 Jun 2001
Posts: 248
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When checking whether an XML element exists, is there any advantage in using
IF CARDINALITY(inputRef.ns:Element[])>0)
over
IF inputRef.ns:Element IS NOT NULL
?
Although the manual covers this point with regards to MRM, I couldn't see anything for XML. |
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| WMBDEV1 |
| Posted: Tue Apr 07, 2009 1:15 am Post subject: |
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Sentinel
Joined: 05 Mar 2009
Posts: 888
Location: UK
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| The check for null will be quicker, especially as the cardinality of the XML elements grows. |
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| rekarm01 |
| Posted: Tue Apr 14, 2009 2:26 am Post subject: Re: IS NOT NULL vs CARDINALITY |
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Grand Master
Joined: 25 Jun 2008
Posts: 1415
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| crossland wrote: |
When checking whether an XML element exists, is there any advantage in using
| Code: |
| IF CARDINALITY(inputRef.ns:Element[]) > 0 |
over
| Code: |
| IF inputRef.ns:Element IS NOT NULL |
? |
"IS NOT NULL" only checks for non-NULL values. It can't check whether field references exist, unless those field references also have non-NULL values. Some field references don't:- XML outer-level tags, with no content, don't have values, (for example: "<outer><inner>inner content</inner></outer>")
- some fields may have an explicitly set NULL value, (for example: "SET fieldRef VALUE = NULL;")
There are at least two ways to check whether a field reference exists, that are much more efficient than CARDINALITY():
| Code: |
| IF EXISTS(inputRef.ns:Element[]) ... |
| Code: |
| IF FIELDTYPE(inputRef.ns:Element) IS NOT NULL ... |
The first of these more obviously expresses the intent of the code.
| crossland wrote: |
| Although the manual covers this point with regards to MRM, I couldn't see anything for XML. |
Where does the manual cover this point with regard to MRM? Field functions and operators act on message tree elements; the underlying parser is not directly relevant. |
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| crossland |
| Posted: Wed Apr 15, 2009 12:40 am Post subject: |
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Master
Joined: 26 Jun 2001
Posts: 248
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Thanks for the reply.
There is a section in "Developing Applications" titled "Querying null values in a message in the MRM domain". There doesn't appear to be a section on querying null values in a message in the XML domains. |
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| kimbert |
| Posted: Wed Apr 15, 2009 2:35 pm Post subject: |
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Jedi Council
Joined: 29 Jul 2003
Posts: 5542
Location: Southampton
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What about this topic: http://publib.boulder.ibm.com/infocenter/wmbhelp/v6r1m0/topic/com.ibm.etools.mft.doc/ac70560_.htm
Important point : Any element in any message tree can have the value NULL; it is not MRM-specific. The MRM parser does have some very powerful and useful settings for detecting null values in the input and automatically setting the equivalent element's value to NULL.
re: the original question, I was wondering how your reference ended up referring to a non-existent field. You are checking LASTMOVE after every MOVE or DECLARE statement, aren't you? |
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