class TermNode

class TermNode extends DrupalSqlBase {
    
    /**
     * The join options between the node and the term node table.
     */
    const JOIN = '[tn].[vid] = [n].[vid]';
    
    /**
     * {@inheritdoc}
     */
    public function query() {
        $query = $this->select('term_node', 'tn')
            ->distinct()
            ->fields('tn', [
            'nid',
            'vid',
        ])
            ->fields('n', [
            'type',
        ]);
        // Because this is an inner join it enforces the current revision.
        $query->innerJoin('term_data', 'td', '[td].[tid] = [tn].[tid] AND [td].[vid] = :vid', [
            ':vid' => $this->configuration['vid'],
        ]);
        $query->innerJoin('node', 'n', static::JOIN);
        return $query;
    }
    
    /**
     * {@inheritdoc}
     */
    public function fields() {
        return [
            'nid' => $this->t('The node revision ID.'),
            'vid' => $this->t('The node revision ID.'),
            'tid' => $this->t('The term ID.'),
        ];
    }
    
    /**
     * {@inheritdoc}
     */
    public function prepareRow(Row $row) {
        // Select the terms belonging to the revision selected.
        $query = $this->select('term_node', 'tn')
            ->fields('tn', [
            'tid',
        ])
            ->condition('n.nid', $row->getSourceProperty('nid'));
        $query->join('node', 'n', static::JOIN);
        $query->innerJoin('term_data', 'td', '[td].[tid] = [tn].[tid] AND [td].[vid] = :vid', [
            ':vid' => $this->configuration['vid'],
        ]);
        $row->setSourceProperty('tid', $query->execute()
            ->fetchCol());
        return parent::prepareRow($row);
    }
    
    /**
     * {@inheritdoc}
     */
    public function getIds() {
        $ids['vid']['type'] = 'integer';
        $ids['vid']['alias'] = 'tn';
        return $ids;
    }

}