Allow for dict keys to only be set if value is not null

[alexgmin]

We have a field that is like this:

    action_timestamps = JSONField(
        default=dict,
        schema={
            'type': 'object',
            'keys': {
                'timestamp_1': {
                    'type': 'string',
                },
                'timestamp_2': {
                    'type': 'string',
                },
            }
        },
    )

Outside of the admin, we set the timestamps only when they are needed.
So for example this could be a valid value for us:

{
    "timestamp_1": "2018-11-19 12:10:02.353829"
}

However, once you edit the model from the admin, that value is set to:

{
    "timestamp_1": "2018-11-19 12:10:02.353829", 
    "timestamp_2": ""
}

Would it be possible to add a keyword to the schema key that makes so the key isn't stored unless it has a non falsy value?

[bhch]

Why can't you ignore the key if it has an empty value?

I think I can add a keyword called skip_if_empty which will omit the key from the final data, but I'd like to know some use-cases and reasons for this feature.

[alexgmin]

It's mostly about not having to store data that isn't needed, and that the admin is not the only source of inputs, so now we would have to replicate the behavior of the library also in other places if we want to keep everything standardized.
The workaround isn't hard (just deleting keys with empty values in an extended model field), so you can close the issue if you don't think it's a good feature.

[bhch]

I'll just keep it open for now. I'll think about it.

I'm also looking to implement validation logic soon, so that would make it easier for you to normalize the data before saving.

[bhch]

Fixed in v2.10.0. A new argument called pre_save_hook can be used for processing json data before saving.