Hello @thiagomajesk Not sure if you are still active.
I encounter the same sort of situation where I need to apply a redirect for the submission of an invalid changeset. I think I have a valid scenario. I will explain why:
The user lands on the page displaying the form, allowing him to add other users (GET)
The user submits the form (POST)
[the form is valid] ->
⠀⠀⠀3. A redirect is done to the next page (GET)
[the form is invalid]
⠀⠀⠀3. The page is re-rendered showing the errors from the invalid changeset (same request)
⠀⠀⠀-> Back to point 2.
- The user presses the ‘Back’ button of the browser.
If he submitted a valid form immediately, when clicking the ‘Back’ button the user will go back to point 1., and a GET is executed, which will not lead to any errors, because the controller action is called and reloads all the data. The flow:
[GET display form page] (A) -> [POST submit form] (B) -> [GET redirect] (.C) -> [GET pressed back button] (back to A)
If he submitted an invalid form, corrected it, and then submits again the flow is:
[GET display form page] (A) -> [POST submit form] (B) -> [POST submit form] (.C) -> [GET redirect] (D) -> [POST pressed back button] (back to B, which is POST)
The latter will lead to an error, when he entered a new user (POST), applied a correction in the form (second POST), and then it got inserted into the DB; then presses back => the form will not include the hidden input containing the ID of the user. So submitting again will cause an error where Ecto cannot find the user that is already saved in DB in the form data.
So I noticed this is how browsers behave when hitting ‘Back’: when the ‘Back’ action returns to a GET request, the server is actually called, and so the controller action will load all the correct data. However, when the ‘Back’ action returns to a POST request (and this happens for a form that must be corrected and leads to multiple subsequent POST requests), nothing is executed on the server; the browser loads the page from some cache. And so, the form will show incorrect data (more specifically here, lacking hidden inputs containing IDs for entities that have been already inserted).
Anyway, besides your quite complex solution (I imagine it is complex as even in your readme of that lib you made, you said it’s only experimental), what would be the best solution? Are there any other trivial solutions (even if it doesn’t provide a smooth UX) to overcome this problem?
Most important is to not raise an error and show an error page to the user, as my form behaves now in such specific case.