TODO
on node save the asin should be renewed? is that the case?
hook_node_save?

convert from 7 to 8
https://www.drupal.org/docs/8/converting-drupal-7-modules-to-drupal-8

system_settings_form() is replaced by \Drupal\Core\Form\ConfigFormBase

Great tutorial: https://befused.com/drupal/drupal8-admin-form-guide

cache api: https://www.chapterthree.com/blog/cache-api-drupal

tabs on the admin settings form?: https://drupal.stackexchange.com/questions/200942/how-do-i-create-tabs-in-an-admin-page
tabs, local tasks: https://programsdream.nl/blog/how-define-local-task-drupal-8
https://www.drupal.org/docs/8/api/menu-api/providing-module-defined-local-tasks

acccesing translate object values: https://drupal.stackexchange.com/questions/202331/how-to-access-the-value-of-a-drupal-core-stringtranslation-translatablemarkup-ob

add assets: https://www.appnovation.com/blog/how-add-js-and-css-assets-drupal-8-theme
https://www.drupal.org/docs/8/creating-custom-modules/adding-stylesheets-css-and-javascript-js-to-a-drupal-8-module

fields: https://www.drupal.org/docs/8/creating-custom-modules/creating-custom-field-types-widgets-and-formatters/overview-creating
https://realize.be/topics/drupal-8-field-api-series
https://capgemini.github.io/drupal/writing-custom-fields-in-drupal-8/  SEHR GUT!
https://www.drupal.org/docs/8/api/entity-api/fieldtypes-fieldwidgets-and-fieldformatters

exception on display formatter, read this:: https://www.deeson.co.uk/labs/how-create-custom-field-use-entity-drupal-8

https://www.deeson.co.uk/labs/how-create-custom-field-use-entity-drupal-8

mit theme erklärung: https://www.sitepoint.com/creating-custom-field-formatters-drupal-8/

templates: https://www.webwash.net/how-to-create-a-custom-field-formatter-in-drupal-8/

widget field settings: https://github.com/thinkshout/ts_recipes/blob/master/drupal8/fields.md
buch: https://books.google.de/books?id=vRhKDwAAQBAJ&pg=PA284&lpg=PA284&dq=drupal+8+storageSettingsForm&source=bl&ots=Z6b8PcQvMH&sig=ACfU3U2YU4e01RK_lTWxCnsJDVVtKDmSOQ&hl=de&sa=X&ved=2ahUKEwjQ46TV4OzlAhWMPOwKHV5NA2EQ6AEwB3oECAkQAQ#v=onepage&q=drupal 8 storageSettingsForm&f=false


View sintegration
---------------
https://medium.com/oleksandr-trotsenko/drupal-8-views-tutorial-for-developers-part-ii-tables-fields-8c753ea38612
https://www.lullabot.com/articles/building-views-query-plugins-for-drupal-8-part-2
https://jbloomfield.codes/2018/06/10/drupal-8-using-drupal-console-to-create-custom-views-field-plugin.html
https://www.orao-web.net/en/ressource-center/how-join-user-table-another-table-views-data
https://www.drupal8.ovh/en/tutoriels/132/views-custom-tables-hook-views-data
https://www.webomelette.com/creating-custom-views-field-drupal-8
https://drupal.stackexchange.com/questions/249963/how-to-add-a-custom-views-filter-handler-for-a-specific-field
https://www.axelerant.com/resources/team-blog/creating-a-custom-view-field-in-drupal-8-to-use-with-workflow-states
https://chromatichq.com/blog/create-custom-views-sort-plugin-drupal-8
https://zanzarra.com/blog/custom-views-filter-plugin-drupal-8-bounding-box-geofield
https://www.foreach.be/blog/how-build-complex-filters-drupal-8?lang=nl
https://marceldoorn.nl/api/drupal/8/2/6/html/sort_2_statistics_last_comment_name_8php_source.html
https://api.drupal.org/api/drupal/core!modules!views!src!Plugin!views!join!JoinPluginBase.php/group/views_join_handlers/8.2.x

custom filter
-----------------
https://www.lullabot.com/articles/creating-a-custom-filter-in-drupal-8 | great article


twig
-----------
print variable from string
https://stackoverflow.com/questions/30347230/twig-print-the-value-of-a-variable-where-the-variable-name-is-string
