class TermStorageSchema

class TermStorageSchema extends SqlContentEntityStorageSchema {
    
    /**
     * {@inheritdoc}
     */
    protected function getEntitySchema(ContentEntityTypeInterface $entity_type, $reset = FALSE) {
        $schema = parent::getEntitySchema($entity_type, $reset);
        if ($data_table = $this->storage
            ->getDataTable()) {
            $schema[$data_table]['indexes'] += [
                'taxonomy_term__tree' => [
                    'vid',
                    'weight',
                    'name',
                ],
                'taxonomy_term__vid_name' => [
                    'vid',
                    'name',
                ],
            ];
        }
        $schema['taxonomy_index'] = [
            'description' => 'Maintains denormalized information about node/term relationships.',
            'fields' => [
                'nid' => [
                    'description' => 'The {node}.nid this record tracks.',
                    'type' => 'int',
                    'unsigned' => TRUE,
                    'not null' => TRUE,
                    'default' => 0,
                ],
                'tid' => [
                    'description' => 'The term ID.',
                    'type' => 'int',
                    'unsigned' => TRUE,
                    'not null' => TRUE,
                    'default' => 0,
                ],
                'status' => [
                    'description' => 'Boolean indicating whether the node is published (visible to non-administrators).',
                    'type' => 'int',
                    'not null' => TRUE,
                    'default' => 1,
                ],
                'sticky' => [
                    'description' => 'Boolean indicating whether the node is sticky.',
                    'type' => 'int',
                    'not null' => FALSE,
                    'default' => 0,
                    'size' => 'tiny',
                ],
                'created' => [
                    'description' => 'The Unix timestamp when the node was created.',
                    'type' => 'int',
                    'not null' => TRUE,
                    'default' => 0,
                ],
            ],
            'primary key' => [
                'nid',
                'tid',
            ],
            'indexes' => [
                'term_node' => [
                    'tid',
                    'status',
                    'sticky',
                    'created',
                ],
            ],
            'foreign keys' => [
                'tracked_node' => [
                    'table' => 'node',
                    'columns' => [
                        'nid' => 'nid',
                    ],
                ],
                'term' => [
                    'table' => 'taxonomy_term_data',
                    'columns' => [
                        'tid' => 'tid',
                    ],
                ],
            ],
        ];
        return $schema;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getSharedTableFieldSchema(FieldStorageDefinitionInterface $storage_definition, $table_name, array $column_mapping) {
        $schema = parent::getSharedTableFieldSchema($storage_definition, $table_name, $column_mapping);
        $field_name = $storage_definition->getName();
        if ($table_name == 'taxonomy_term_field_data') {
            // Remove unneeded indexes.
            unset($schema['indexes']['taxonomy_term_field__vid__target_id']);
            unset($schema['indexes']['taxonomy_term_field__description__format']);
            switch ($field_name) {
                case 'weight':
                    // Improves the performance of the taxonomy_term__tree index defined
                    // in getEntitySchema().
                    $schema['fields'][$field_name]['not null'] = TRUE;
                    break;
                case 'name':
                    $this->addSharedTableFieldIndex($storage_definition, $schema, TRUE);
                    break;
            }
        }
        return $schema;
    }
    
    /**
     * {@inheritdoc}
     */
    protected function getDedicatedTableSchema(FieldStorageDefinitionInterface $storage_definition, ContentEntityTypeInterface $entity_type = NULL) {
        $dedicated_table_schema = parent::getDedicatedTableSchema($storage_definition, $entity_type);
        // Add an index on 'bundle', 'delta' and 'parent_target_id' columns to
        // increase the performance of the query from
        // \Drupal\taxonomy\TermStorage::getVocabularyHierarchyType().
        if ($storage_definition->getName() === 'parent') {
            
            /** @var \Drupal\Core\Entity\Sql\DefaultTableMapping $table_mapping */
            $table_mapping = $this->storage
                ->getTableMapping();
            $dedicated_table_name = $table_mapping->getDedicatedDataTableName($storage_definition);
            unset($dedicated_table_schema[$dedicated_table_name]['indexes']['bundle']);
            $dedicated_table_schema[$dedicated_table_name]['indexes']['bundle_delta_target_id'] = [
                'bundle',
                'delta',
                $table_mapping->getFieldColumnName($storage_definition, 'target_id'),
            ];
        }
        return $dedicated_table_schema;
    }

}