I have created a D8 custom field that extends FieldBaseItem. It is already in use storing data.

How do I get the schema updated in the database, for an existing field?

What I’ve done:

I have added a new column by adding to propertyDefinitions and schema() accordingly.

Here’s an example schema. Let’s say I just added the admin column.

  /**    * {@inheritdoc}    */   public static function schema(FieldStorageDefinitionInterface $  field_definition) {     $  schema = [       'columns' => [         'state' => [           'type' => 'varchar',           'length' => 2         ],         'admin' => [           'type' => 'int',           'size' => 'tiny'         ],         ... 

I’ve found posts on how to do this in hook_update_N in D7, but it’s unclear how to do this in D8.