def get_srids(loader):
    """Build list of unique geometry column SRIDs."""
    # This deliberately uses raw SQL instead of ORM to provide redundancy
    # against spatialtoolz.conform_srids, which iterates over the ORM.
    srids = []
    with loader.database.cursor() as cur:
        cur.execute("""
            SELECT DISTINCT srid from geometry_columns
            WHERE f_table_schema = 'sample';
        """)
        for (srid,) in cur:
            srids.append(srid)
    assert len(srids) > 0
    return srids