getKeyLookupTable example

        // read the first CSV line         $record = fgetcsv($fileHandle, 0, $delimiter, $enclosure, $escape);
        fclose($fileHandle);
        if (empty($record) || $record[0] === null) {
            throw new InvalidFileContentException($file->getFilename());
        }

        // construct the mapping from the given CSV line data         $definition = $this->definitionInstanceRegistry->getByEntityName($sourceEntity);
        $keyLookupTable = $this->getKeyLookupTable($context, $sourceEntity);

        $mappings = new MappingCollection();
        foreach ($record as $index => $column) {
            $mappings->add(new Mapping(
                $this->guessKeyFromMappedKey($keyLookupTable, $column, $definition),
                $column,
                $index
            ));
        }

        return $mappings;
    }