Method getIndexValue

txn.go:660–706

getIndexValue is used to get the IndexSchema and the value used to scan the index given the parameters. This handles prefix based scans when the index has the "_prefix" suffix. The index must support prefix iteration.

(table, index string, args ...interface{})

// scans when the index has the "_prefix" suffix. The index must support
// prefix iteration.
func (txn *Txn) getIndexValue(table, index string, args ...interface{}) (*IndexSchema, []byte, error) {
	// Get the table schema
	tableSchema, ok := txn.db.schema.Tables[table]
	if !ok {
		return nil, nil, fmt.Errorf("invalid table '%s'", table)
	}

	// Check for a prefix scan
	prefixScan := false
	if strings.HasSuffix(index, "_prefix") {
		index = strings.TrimSuffix(index, "_prefix")
		prefixScan = true
	}

	// Get the index schema
	indexSchema, ok := tableSchema.Indexes[index]
	if !ok {
		return nil, nil, fmt.Errorf("invalid index '%s'", index)
	}

	// Hot-path for when there are no arguments
	if len(args) == 0 {
		return indexSchema, nil, nil
	}

	// Special case the prefix scanning
	if prefixScan {
		prefixIndexer, ok := indexSchema.Indexer.(PrefixIndexer)
		if !ok {
			return indexSchema, nil,
				fmt.Errorf("index '%s' does not support prefix scanning", index)
		}

		val, err := prefixIndexer.PrefixFromArgs(args...)
		if err != nil {
			return indexSchema, nil, fmt.Errorf("index error: %v", err)
		}
		return indexSchema, val, err
	}

	// Get the exact match index
	val, err := indexSchema.Indexer.FromArgs(args...)
	if err != nil {
		return indexSchema, nil, fmt.Errorf("index error: %v", err)
	}
	return indexSchema, val, err
}

// ResultIterator is used to iterate over a list of results from a query on a table.
//