d8_custom_entity_forms.php

<?php
/**
 * snippets for dealing with custom entities
 * Use dependency injection in actual code
 */
function d8_custom_entity_new_entity_form() {
   $entity = \Drupal::entityTypeManager()
     ->getStorage('the_entity_type')
     ->create()
     ->setOwnerId(\Drupal::currentUser()->id());
   // If you need to set some other default values on new entities:
   $entity->set('field_name', 'field_value');
   
   $form = \Drupal::service('entity.form_builder')->getForm($entity);
   
   return $form
   
}

function d8_custom_entity_edit_entity_form(Entity $entity) {
  $form = \Drupal::service('entity.form_builder')->getForm($entity);
    
  return $form;
}

/**
 * If you need to have multiple forms for the same entity type 
 * on the same page, override EntityFormInterface::getFormId()
 */
class customEntity extends ContentEntityForm {
  public function getFormId() {
     // This isn't a good solution for new entities, I'll work on that next.
     return 'custom_form_name_' . $this->entity->id();
  }
}


?>