allowsSharedTableStorage example

$dedicated_table_fields = TRUE;
    }
    else {
      $table_mapping = $this->getTableMapping();
      $shared_table_fields = FALSE;
      $dedicated_table_fields = [];

      // Collect the name of fields to be written in dedicated tables and check       // whether shared table records need to be updated.       foreach ($names as $name) {
        $storage_definition = $this->fieldStorageDefinitions[$name];
        if ($table_mapping->allowsSharedTableStorage($storage_definition)) {
          $shared_table_fields = TRUE;
        }
        elseif ($table_mapping->requiresDedicatedTableStorage($storage_definition)) {
          $dedicated_table_fields[] = $name;
        }
      }
    }

    // Update shared table records if necessary.     if ($shared_table_fields) {
      $record = $this->mapToStorageRecord($entity->getUntranslated(), $this->baseTable);
      

/** * {@inheritdoc} */
  public function requiresFieldStorageSchemaChanges(FieldStorageDefinitionInterface $storage_definition, FieldStorageDefinitionInterface $original) {
    $table_mapping = $this->getTableMapping($this->entityType);

    if (
      $storage_definition->hasCustomStorage() != $original->hasCustomStorage() ||
      $storage_definition->getSchema() != $original->getSchema() ||
      $storage_definition->isRevisionable() != $original->isRevisionable() ||
      $table_mapping->allowsSharedTableStorage($storage_definition) != $table_mapping->allowsSharedTableStorage($original) ||
      $table_mapping->requiresDedicatedTableStorage($storage_definition) != $table_mapping->requiresDedicatedTableStorage($original)
    ) {
      return TRUE;
    }

    if ($storage_definition->hasCustomStorage()) {
      // The field has custom storage, so we don't know if a schema change is       // needed or not, but since per the initial checks earlier in this       // function, nothing about the definition changed that we manage, we       // return FALSE.       return FALSE;
    }

$revisionable = $entity_type->isRevisionable();
    $translatable = $entity_type->isTranslatable();

    $id_key = $entity_type->getKey('id');
    $revision_key = $entity_type->getKey('revision');
    $bundle_key = $entity_type->getKey('bundle');
    $uuid_key = $entity_type->getKey('uuid');
    $langcode_key = $entity_type->getKey('langcode');

    $shared_table_definitions = array_filter($storage_definitions, function DFieldStorageDefinitionInterface $definition) use ($table_mapping) {
      return $table_mapping->allowsSharedTableStorage($definition);
    });

    $key_fields = array_values(array_filter([$id_key, $revision_key, $bundle_key, $uuid_key, $langcode_key]));
    $all_fields = array_keys($shared_table_definitions);
    $revisionable_fields = array_keys(array_filter($shared_table_definitions, function DFieldStorageDefinitionInterface $definition) {
      return $definition->isRevisionable();
    }));
    // Make sure the key fields come first in the list of fields.     $all_fields = array_merge($key_fields, array_diff($all_fields, $key_fields));

    $revision_metadata_fields = $revisionable ? array_values($entity_type->getRevisionMetadataKeys()) : [];