This is used when indexing Content and matching Content fields. Actual format of the returned value depends on the search engine implementation, meaning engines should override common implementation as needed, but the same input should be handled across engines.
See also: eZ\Publish\SPI\Search\FieldType
 /**
  * Map search field value to solr value using FieldValueMapper.
  *
  * @param mixed $value
  * @param \eZ\Publish\SPI\Search\FieldType $searchFieldType
  *
  * @return mixed
  */
 protected function mapSearchFieldValue($value, FieldType $searchFieldType = null)
 {
     if (null === $searchFieldType) {
         return $value;
     }
     $searchField = new SearchField('field', $value, $searchFieldType);
     $value = (array) $this->fieldValueMapper->map($searchField);
     return current($value);
 }
 protected function writeField(XmlWriter $xmlWriter, Field $field)
 {
     foreach ((array) $this->fieldValueMapper->map($field) as $value) {
         $xmlWriter->startElement('field');
         $xmlWriter->writeAttribute('name', $this->nameGenerator->getTypedName($field->name, $field->type));
         $xmlWriter->text($value);
         $xmlWriter->endElement();
     }
 }
 /**
  * Converts given $document to a hash format that can be JSON encoded
  * to get a document _source.
  *
  * Implemented in a separate method because of a recursion needed to
  * handle nested documents.
  *
  * @param \eZ\Publish\Core\Search\Elasticsearch\Content\Document $document
  *
  * @return array
  */
 protected function getDocumentHash(Document $document)
 {
     $hash = array();
     foreach ($document->fields as $field) {
         if ($field->type instanceof DocumentField) {
             $documents = $this->fieldValueMapper->map($field);
             $values = array();
             foreach ($documents as $document) {
                 $values[] = $this->getDocumentHash($document);
             }
         } else {
             $values = (array) $this->fieldValueMapper->map($field);
         }
         $name = $this->nameGenerator->getTypedName($field->name, $field->type);
         if (count($values) === 1) {
             $hash[$name] = reset($values);
         } else {
             $hash[$name] = $values;
         }
     }
     return $hash;
 }