Detecting links to deleted rows

Anvil Q&A
1

I have a table called events and a table called usereventyns which has a column linked to a single event.
If I delete an event row and then examine the usereventyns in the table editor the rows linked to the now deleted event show ‘Unknown Row’ in the link column. How can I find these ‘orphaned’ usereventyns in code? Essentially, if I delete an event I want to ensure that any linked rows in usereventyns are also deleted.

I tried something along the lines of this

Code Sample:

yns=app_tables.usereventyns.search()
    for yn in yns:
      yneventlink=yn['eventlink']
      if yneventlink = 'Unknown Row' ....

but it obviously wouldn't allow a string as a link
2

You can clean up those rows when you delete the event, so that you don’t have links to unknown rows to worry about.

1 Like
3

Thanks, that was my plan but I wanted to be able to find and delete orphans just in case something went wrong during an event deletion.

4

You can try iterating through all the links in a multiple link field, adding each good link to a new set of links, doing the add inside a try/except, so that unknown links don’t get added. It’d take some experimentation to get it right, but catching the exception that happens when you try to access a column through the orphaned link is the only way to know that it’s an orphaned link.

1 Like
5

Yup, that works. Thanks again.