Blank result for a long GREL expression parsing XML data

Support and Helpdesk
1

Hi everyone,

I am parsing XML data with a long GREL expression, but while the preview shows the result I expect, the column produced has only blank cells. Do you have an idea of why?

I am starting with data like "SDC 12-4142", then harvesting an API by using this URL:

https://catalogue.bnf.fr/api/SRU?version=1.2&operation=searchRetrieve&query=bib.cote%20adj%20"SDC+12-4142"&recordSchema=unimarcxchange&maximumRecords=20&startRecord=1

Then I get the XML and try to parse it in a new column by applying this GREL expression:

forEach(value.parseXml().select("mxc|record"),record, if(startsWith(record.select("mxc|datafield[tag=930]")[0].select("mxc|subfield[code=a]")[0].xmlText(), "SDC"),record.select("mxc|datafield[tag=215]")[0].select("mxc|subfield[code=a]")[0].xmlText(), None)).join(" | ")

In the preview, the result I expect ("2 disques compacts | 1 disque compact (55 min 19 s)") shows up but when I click OK the column is blank.

I noticed the same behavior with v. 3.7.2 and v. 3.7.6.

Thank you for any help you could give me and sorry if a similar question was already asked!

Bertrand Caron

2

The most common reason for the type of behavior that you describe is
that the preview window is showing an array, which OpenRefine can't
store in a cell, but I just tried your expression with OpenRefine
3.7.6 and it worked fine for me.

Here's what I did:

  • Created a project from the clipboard and pasted your URL into the window
  • Used Add column by fetching URL to get the XL
  • Used Add column based on this column with your GREL expression
  • Confirmed that it produced your desired result.

On the other hand, if I leave of the final join('|'), the preview
window shows [ "2 disques compacts", "1 disque compact (55 min 19 s)"
] which is an array that's not storable (we should probably highlight
this fact a little better in the preview window).

Tom

3

Thank you very much @tfmorris . I was told about this issue with arrays earlier, but adding join() did not seem to help.

After reading your answer, I switched to my personal computer and it worked. Don't know why, but it doesn't matter really.

Thanks again!

1 Like
4

Glad to help. It is a problematic design which has been around forever, unfortunately. The first time it was discussed was 2011.

https://github.com/OpenRefine/OpenRefine/issues/434

https://github.com/OpenRefine/OpenRefine/issues/443

https://github.com/OpenRefine/OpenRefine/issues/1088

https://github.com/OpenRefine/OpenRefine/issues/1475

https://github.com/OpenRefine/OpenRefine/issues/4823

There is a similar issue with other unstorable intermediary types (JSON object, XML elements).
We need a better mechanism for signalling to the user that these are not storable in a cell.

Tom