class TermLocalizedTranslation

class TermLocalizedTranslation extends Term {
    
    /**
     * {@inheritdoc}
     */
    public function query() {
        // Ideally, the query would return rows for each language for each taxonomy
        // term with the translations for both the name and description or just the
        // name translation or just the description translation. That query quickly
        // became complex and would be difficult to maintain.
        // Therefore, build a query based on i18nstrings table where each row has
        // the translation for only one property, either name or description. The
        // method prepareRow() is then used to obtain the translation for the other
        // property.
        $query = parent::query();
        $query->addField('td', 'language', 'td.language');
        // Add in the property, which is either name or description.
        // Cast td.tid as char for PostgreSQL compatibility.
        $query->leftJoin('i18n_strings', 'i18n', 'CAST([td].[tid] AS CHAR(255)) = [i18n].[objectid]');
        $query->condition('i18n.type', 'term');
        $query->addField('i18n', 'lid');
        $query->addField('i18n', 'property');
        // Add in the translation for the property.
        $query->innerJoin('locales_target', 'lt', '[i18n].[lid] = [lt].[lid]');
        $query->addField('lt', 'language', 'lt.language');
        $query->addField('lt', 'translation');
        return $query;
    }
    
    /**
     * {@inheritdoc}
     */
    public function prepareRow(Row $row) {
        $language = $row->getSourceProperty('ltlanguage');
        $row->setSourceProperty('language', $language);
        $tid = $row->getSourceProperty('tid');
        // If this row has been migrated it is a duplicate then skip it.
        if ($this->idMap
            ->lookupDestinationIds([
            'tid' => $tid,
            'language' => $language,
        ])) {
            return FALSE;
        }
        // Save the translation for this property.
        $property = $row->getSourceProperty('property');
        $row->setSourceProperty($property . '_translated', $row->getSourceProperty('translation'));
        // Get the translation, if one exists, for the property not already in the
        // row.
        $other_property = $property == 'name' ? 'description' : 'name';
        $query = $this->select('i18n_strings', 'i18n')
            ->fields('i18n', [
            'lid',
        ])
            ->condition('i18n.type', 'term')
            ->condition('i18n.property', $other_property)
            ->condition('i18n.objectid', $tid);
        $query->leftJoin('locales_target', 'lt', '[i18n].[lid] = [lt].[lid]');
        $query->condition('lt.language', $language);
        $query->addField('lt', 'translation');
        $results = $query->execute()
            ->fetchAssoc();
        if ($results) {
            $row->setSourceProperty($other_property . '_translated', $results['translation']);
        }
        else {
            // The translation does not exist.
            $row->setSourceProperty($other_property . '_translated', NULL);
        }
        return parent::prepareRow($row);
    }
    
    /**
     * {@inheritdoc}
     */
    public function fields() {
        $fields = [
            'language' => $this->t('Language for this term.'),
            'name_translated' => $this->t('Term name translation.'),
            'description_translated' => $this->t('Term description translation.'),
        ];
        return parent::fields() + $fields;
    }
    
    /**
     * {@inheritdoc}
     */
    public function getIds() {
        $ids['language']['type'] = 'string';
        $ids['language']['alias'] = 'lt';
        return parent::getIds() + $ids;
    }

}