class FieldableEntity

abstract class FieldableEntity extends DrupalSqlBase {
    
    /**
     * Returns all non-deleted field instances attached to a specific entity type.
     *
     * Typically, getFields() is used in the prepareRow method of a source plugin
     * to get a list of all the field instances of the entity. A source plugin can
     * then loop through the list of fields to do any other preparation before
     * processing the row. Typically, a source plugin will use getFieldValues()
     * to get the values of each field.
     *
     * @param string $entity_type
     *   The entity type ID.
     * @param string|null $bundle
     *   (optional) The bundle.
     *
     * @return array[]
     *   The field instances, keyed by field name.
     */
    protected function getFields($entity_type, $bundle = NULL) {
        $query = $this->select('field_config_instance', 'fci')
            ->fields('fci')
            ->condition('fci.entity_type', $entity_type)
            ->condition('fci.bundle', $bundle ?? $entity_type)
            ->condition('fci.deleted', 0);
        // Join the 'field_config' table and add the 'translatable' setting to the
        // query.
        $query->leftJoin('field_config', 'fc', '[fci].[field_id] = [fc].[id]');
        $query->addField('fc', 'translatable');
        return $query->execute()
            ->fetchAllAssoc('field_name');
    }
    
    /**
     * Retrieves field values for a single field of a single entity.
     *
     * Typically, getFieldValues() is used in the prepareRow method of a source
     * plugin where the return values are placed on the row source.
     *
     * @param string $entity_type
     *   The entity type.
     * @param string $field
     *   The field name.
     * @param int $entity_id
     *   The entity ID.
     * @param int|null $revision_id
     *   (optional) The entity revision ID.
     * @param string $language
     *   (optional) The field language.
     *
     * @return array
     *   The raw field values, keyed and sorted by delta.
     */
    protected function getFieldValues($entity_type, $field, $entity_id, $revision_id = NULL, $language = NULL) {
        $table = (isset($revision_id) ? 'field_revision_' : 'field_data_') . $field;
        $query = $this->select($table, 't')
            ->fields('t')
            ->condition('entity_type', $entity_type)
            ->condition('entity_id', $entity_id)
            ->condition('deleted', 0)
            ->orderBy('delta');
        if (isset($revision_id)) {
            $query->condition('revision_id', $revision_id);
        }
        // Add 'language' as a query condition if it has been defined by Entity
        // Translation.
        if ($language) {
            $query->condition('language', $language);
        }
        $values = [];
        foreach ($query->execute() as $row) {
            foreach ($row as $key => $value) {
                $delta = $row['delta'];
                if (strpos($key, $field) === 0) {
                    $column = substr($key, strlen($field) + 1);
                    $values[$delta][$column] = $value;
                }
            }
        }
        return $values;
    }
    
    /**
     * Checks if an entity type uses Entity Translation.
     *
     * @param string $entity_type
     *   The entity type.
     *
     * @return bool
     *   Whether the entity type uses entity translation.
     */
    protected function isEntityTranslatable($entity_type) {
        return in_array($entity_type, $this->variableGet('entity_translation_entity_types', []), TRUE);
    }
    
    /**
     * Gets an entity source language from the 'entity_translation' table.
     *
     * @param string $entity_type
     *   The entity type.
     * @param int $entity_id
     *   The entity ID.
     *
     * @return string|bool
     *   The entity source language or FALSE if no source language was found.
     */
    protected function getEntityTranslationSourceLanguage($entity_type, $entity_id) {
        try {
            return $this->select('entity_translation', 'et')
                ->fields('et', [
                'language',
            ])
                ->condition('entity_type', $entity_type)
                ->condition('entity_id', $entity_id)
                ->condition('source', '')
                ->execute()
                ->fetchField();
        } catch (\Exception $e) {
            return FALSE;
        }
    }

}