Strange deployment filtering in Campaigns

[heidimok]

Problem

It appears like we are only showing one deployment per campaign at times. We have some weird filtering in order to try to retrieve only the latest draft of each deployment. But it's filtering out anything with duplicate model_instance_uuid values. The problem is a Change object doesn't get a model_instance_uuid value until it's published, so we will only display a single unpublished deployment.

Additional Information

• A fix to this issue might have caused the problem we are seeing: https://github.com/NASA-IMPACT/admg-backend/issues/366
• What's weird is null values (as we have on model_instance_uuid should be treated as distinct by the database)
• Maybe we are using a really old version of postgres?
• It seems like the DB we're using in staging should be treating those values as distinct, so it'll take some digging

[edkeeble]

Oh, reading the postgresql DISTINCT docs further:

Obviously, two rows are considered distinct if they differ in at least one column value. Null values are considered equal in this comparison.

So I guess we just need to update this query to not use DISTINCT.