def get_columns_diff(changes):
    """Add the changed columns as a diff attribute.

    - changes: a list of changes (get_model_changes query.all())

    Return: the same list, to which elements we added a "diff"
    attribute containing the changed columns. Diff defaults to [].
    """
    for change in changes:
        change.diff = []
        elt_changes = change.get_changes()
        if elt_changes:
            change.diff = elt_changes.columns
    return changes
