code: func (f Uint64Field) Inc() (val uint64, err error) {
  	val, err = f.Get()
  	if err != nil {
  		if err == leveldb.ErrNotFound {
  			val = 0
  		} else {
  			return 0, err
  		}
  	}
  	val++
  	return val, f.Put(val)
  }
docs: // Inc increments a uint64 value in the database.
  // This operation is not goroutine save.