Updated Admin integration documentation to clarify how to save custom form values

[matthewhegarty]

Problem

Documentation was not clear on how to persist custom form selections.

Closes #1740

Solution

Updated the docs to clarify how to do this.

Acceptance Criteria

• Tested documentation locally

[eldavo]

@matthewhegarty I reviewed the docs and compared it with my implementation and am running into two issues. These may not be bugs per se with the documentation because my implementation uses a compound key with 4 attributes (You helped me on Stackoverflow with https://stackoverflow.com/questions/77085694/django-import-export-customize-admin-missing-field-error). Here are the two issues I'm running into:

1. I must override after_import_instance in the corresponding resource , e.g.

 def after_import_instance(self, instance, new, row_number=None, **kwargs):
    instance.league = kwargs["league"]
    instance.season = kwargs["season"]
    pass

2. I can import just fine, but when I try to do an update via CSV I receive the following error for all lines:

...
Line number: 1 - (1062, "Duplicate entry '3-2021' for key 'unique_team_season_key'")
...

However if I put columns and values in for league and season, updates work perfectly, so there's something going on with update and the customized admin if I am relying for form values to supply part of a compound key, either with documentation or my current implementation.

[matthewhegarty]

Hi Dave

It looks like 1062 is coming from the DB itself i.e. clashing on a duplicate key. This means that import_export has not detected that your row is an update and is trying to create a new row. So something is wrong with the import logic in detecting existing rows. From what you say, presumably the 'league' and 'season' fields have to be present in order for the import process to detect that you have an existing entry.

The best thing to do is to step through with a debugger and see directly what the issue is. If it is a bug, please raise a new issue, or if you need any further help the best place to post is Stack Overflow.

[eldavo]

Thanks Matthew, will do.