table actions with preempt = True get called twice

What is your Use Case?

I am not sure, but from what I see, preemptive_actions are for use case, when you want to perform an action without rendering of the table, or loading of the data.

So it is very usable for any AJAX action. It requires the action to return something true (like json response), then it just return the response to browser and not continue further.

The normal action on the other hand, first loads the data. Then in calls action, that should alter the data in some way. Then it renders.

I can see, that it can be handy to first execute the action, then load the data and render a table in one request. So yeah, just adding a condition, that will not call preempt actions in 'maybe_handle' method should be enough. Though I am not sure how you will pass Action errors this way. But given the .. attribute:: preempt docs, I would consider this as a bug.

There are already mechanisms in place for the ajax use case, and this is not one of them and does not really relate to the ajax usage.

The use case is something like this..... let's say I want to have an action that changes the row state from state A to state B. This is a quick state change, no fancy ajax action is needed. The code as it currently is, will fire my action twice. Once on the preempt phase (where I need to execute, because I don't want the table data loaded - I am changing the state of the data), then it loads the data (now my table shows stateB for the row), then it fires my action again (which will fail since my row is already in state B).

The action error handling is the same either way, add messages as needed back into the response.

Ok, agree. Please file a bug for this, it should definitely execute the action only once.

It should be one line fix from what I see.

Thanks Ladislav Smola, that solved my question.