Built in method to prevent deletion of rows with linked field

Feature Requests
#1

Is there any built in method in anvil to prevent deletion of rows with linked fields so that one does not get TableError.

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#2

Hi @alexri,

At the moment there isn’t a way to do this, but I like the suggestion. I’ve moved this to feature requests so we can gauge interest!

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#3

In SQL foreign-key terms, this would be an ON DELETE RESTRICT, as opposed to the current ON DELETE NO ACTION.

If you were to do this SQL-style, then the restriction would be declared at the point-of-reference, i.e., the column that links to the target, not at the target itself.

Another facet would be how to report such an attempt to the calling code.

  • Pythonic: raise a distinct Exception
  • C-style: return a distinct value.

In either case, it may be useful to know the row that “objected” to the delete. Otherwise, one might have a fairly long database search to find it.

#4

I’m all in favor of exposing a few more SQL mechanisms. Specifying columns as unique would be another good one, along with restricting deletion of linked columns or cascading deletion.

#5

There have already been steps in that direction. For example, you can mark columns to be indexed in three different ways.

For these more-expensive versions of update and delete, rather than impose the overhead on all existing calls in all apps, it may be wise to implement new functions, e.g., checked_update and checked_delete.

Yes, it means that the folks writing the calls will have to think more about what they’re doing. That’s not always a bad thing. :wink:

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