[Fixed]-Unique column value in django

I think you have to do this manually in your view.
Each time you are adding a new media or modifying a media you need to check whether the location you are setting is already in the table or not. If it is already in the table then you have to modify the former media location and set it to None.
Be careful when deleting a media because if this media has a location maybe you’ll want to set the location back to another media.