docs: def migrate_database(adapter):
      """Migrate an old loqusdb instance to 1.0
      
      Args:
          adapter
      
      Returns:
          nr_updated(int): Number of variants that where updated
      """
      
      all_variants = adapter.get_variants()
      nr_variants = all_variants.count()
      nr_updated = 0
      with progressbar(all_variants, label="Updating variants", length=nr_variants) as bar:
          for variant in bar:
              # Do not update if the variants have the correct format
              if 'chrom' in variant:
                  continue
              nr_updated += 1
              splitted_id = variant['_id'].split('_')
              
              chrom = splitted_id[0]
              start = int(splitted_id[1])
              ref = splitted_id[2]
              alt = splitted_id[3]
              
              # Calculate end
              end = start + (max(len(ref), len(alt)) - 1)
              
              adapter.db.variant.find_one_and_update(
                  {'_id': variant['_id']},
                  {
                      '$set': {
                          'chrom': chrom,
                          'start': start,
                          'end': end
                      }
                  }
              )
      
      return nr_updated