def add_source_parent_project_names(project_details_df):
    """
    Join the parent project names to the details for each project.
    :param DataFrame project_details_df: the project details DataFrame
    :return: DataFrame
    """
    temp_df = project_details_df[['source_project_name', 'source_project_id']
        ].copy()
    temp_df.rename(columns={'source_project_name':
        'source_project_parent_name'}, inplace=True)
    project_details_df = project_details_df.merge(temp_df, left_on=
        'source_project_parent_id', right_on='source_project_id', how=
        'left', suffixes=(None, '_delete'))
    return project_details_df.drop(columns=['source_project_id_delete'])
