code: func (f Index) DeleteInBatch(batch *leveldb.Batch, keyFields Item) (err error) {
  	key, err := f.encodeKeyFunc(keyFields)
  	if err != nil {
  		return err
  	}
  	batch.Delete(key)
  	return nil
  }
docs: // DeleteInBatch is the same as Delete just the operation
  // is performed on the batch instead on the database.