Why is the default display for a custom entity blank?

Question

I have two custom entities, which use the same boilerplate framework. I can add content to both, but one displays fine (sample) and the other is just blank (chemical).

The twig templates for both are:

module/templates/chemical.html.twig

<div{{ attributes.addClass('chemical') }}>
{% if content %}
  {{- content -}}
{% endif %}
</div>

and in module/templates/sample.html.twig

<div{{ attributes.addClass('sample') }}>
{% if content %}
  {{- content -}}
{% endif %}
</div>

There are no error messages. Is there something in the entity definition file module/src/Entity/Chemical.php that might be throwing off the display, but still allowing the data to be entered and saved correctly?

Here is the Chemical Entity definition:

<?php

namespace Drupal\lab_system\Entity;

use Drupal\Core\Entity\EntityStorageInterface;
use Drupal\Core\Field\BaseFieldDefinition;
use Drupal\Core\Field\FieldStorageDefinitionInterface;
use Drupal\Core\Entity\ContentEntityBase;
use Drupal\Core\Entity\EntityTypeInterface;
use Drupal\user\UserInterface;

/**
 * Defines the Chemical entity.
 *
 * @ingroup lab_system
 *
 * @ContentEntityType(
 *   id = "chemical",
 *   label = @Translation("Chemical"),
 *   handlers = {
 *     "view_builder" = "Drupal\Core\Entity\EntityViewBuilder",
 *     "list_builder" = "Drupal\lab_system\ChemicalListBuilder",
 *     "views_data" = "Drupal\lab_system\Entity\ChemicalViewsData",
 *
 *     "form" = {
 *       "default" = "Drupal\lab_system\Form\ChemicalForm",
 *       "add" = "Drupal\lab_system\Form\ChemicalForm",
 *       "edit" = "Drupal\lab_system\Form\ChemicalForm",
 *       "delete" = "Drupal\lab_system\Form\ChemicalDeleteForm",
 *     },
 *     "access" = "Drupal\lab_system\ChemicalAccessControlHandler",
 *     "route_provider" = {
 *       "html" = "Drupal\lab_system\ChemicalHtmlRouteProvider",
 *     },
 *   },
 *   base_table = "chemical",
 *   admin_permission = "administer chemical entities",
 *   entity_keys = {
 *     "id" = "id",
 *     "label" = "name",
 *     "smiles" = "smiles",
 *     "boiling_point" = "boiling_point",
 *     "tid" = "tid",
 *     "alternate_tid" = "alternate_tid",
 *   },
 *   links = {
 *     "canonical" = "/admin/structure/lab_system/chemical/{chemical}",
 *     "add-form" = "/admin/structure/lab_system/chemical/add",
 *     "edit-form" = "/admin/structure/lab_system/chemical/{chemical}/edit",
 *     "delete-form" = "/admin/structure/lab_system/chemical/{chemical}/delete",
 *     "collection" = "/admin/structure/lab_system/chemical",
 *   },
 *   field_ui_base_route = "chemical.settings"
 * )
 */
class Chemical extends ContentEntityBase implements ChemicalInterface {

  /**
   * {@inheritdoc}
   */
  public function getAlternateNames() {
    return $this->get('alternate_names')->values;
  }

  /**
   * {@inheritdoc}
   */
  public function getName() {
    return $this->get('name')->value;
  }

  /**
   * {@inheritdoc}
   */
  public function setName($name) {
    $this->set('name', $name);
    return $this;
  }

  /**
   * {@inheritdoc}
   */
  public function getSmiles() {
    return $this->get('smiles')->value;
  }

  /**
   * {@inheritdoc}
   */
  public function getBoilingPoint() {
    return $this->get('boiling_point')->value;
  }

  /**
   * {@inheritdoc}
   */
  public function setBoilingPoint($bp) {
    $this->set('boiling_point', $bp);
    return $this;
  }

  /**
   * {@inheritdoc}
   */
  public static function baseFieldDefinitions(EntityTypeInterface $entity_type) {
$fields = parent::baseFieldDefinitions($entity_type);

$fields['name'] = BaseFieldDefinition::create('string')
  ->setLabel(t('Name'))
  ->setDescription(t('The name of the Chemical entity.'))
  ->setSettings(array(
    'max_length' => 50,
    'text_processing' => 0,
  ))
  ->setDefaultValue('')
  ->setDisplayOptions('view', array(
    'label' => 'above',
    'type' => 'string',
    'weight' => -4,
  ))
  ->setDisplayOptions('form', array(
    'type' => 'string_textfield',
    'weight' => -4,
  ))
  ->setDisplayConfigurable('form', TRUE)
  ->setDisplayConfigurable('view', TRUE);

$fields['alternate_names'] = BaseFieldDefinition::create('string')
  ->setLabel(t('Alternate Name'))
  ->setDescription(t('Alternate Names.'))
  ->setCardinality(FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED)
  ->setSettings(array(
    'max_length' => 50,
    'text_processing' => 0,
  ))
  ->setDefaultValue('')
  ->setDisplayOptions('view', array(
    'label' => 'above',
    'type' => 'string',
    'weight' => -4,
  ))
  ->setDisplayOptions('form', array(
    'type' => 'string_textfield',
    'weight' => -4,
  ))
  ->setDisplayConfigurable('form', TRUE)
  ->setDisplayConfigurable('view', TRUE);

$fields['smiles'] = BaseFieldDefinition::create('string')
  ->setLabel(t('SMILES'))
  ->setDescription(t('The SMILES structure.'))
  ->setSettings(array(
    'max_length' => 100,
    'text_processing' => 0,
  ))
  ->setDefaultValue('')
  ->setDisplayOptions('view', array(
    'label' => 'above',
    'type' => 'string',
    'weight' => -4,
  ))
  ->setDisplayOptions('form', array(
    'type' => 'string_textfield',
    'weight' => -4,
  ))
  ->setDisplayConfigurable('form', TRUE)
  ->setDisplayConfigurable('view', TRUE);

$fields['boiling_point'] = BaseFieldDefinition::create('float')
  ->setLabel(t('Boiling Point'))
  ->setDescription(t('The boiling point of the compound.'))
  ->setDefaultValue(TRUE)
  ->setDisplayOptions('view', array(
    'label' => 'above',
    'type' => 'float',
    'weight' => 0,
  ))
  ->setDisplayOptions('form', array(
    'type' => 'string_textfield',
    'weight' => -4,
  ))
  ->setDisplayConfigurable('form', TRUE)
  ->setDisplayConfigurable('view', TRUE);

$fields['tid'] = BaseFieldDefinition::create('entity_reference')
  ->setLabel(t('Chemical Family'))
  ->setDescription(t('The family to which this chemical belongs.'))
  ->setSetting('target_type', 'taxonomy_term')
  ->setSetting('handler', 'default')
  ->setTranslatable(TRUE)
  ->setDisplayOptions('view', array(
    'label' => 'above',
    'type' => 'integer',
    'weight' => 0,
  ))
  ->setDisplayOptions('form', array(
    'type' => 'entity_reference_autocomplete',
    'weight' => 5,
    'settings' => array(
      'match_operator' => 'CONTAINS',
      'size' => '60',
      'autocomplete_type' => 'tags',
      'placeholder' => '',
    ),
  ))
  ->setDisplayConfigurable('form', TRUE)
  ->setDisplayConfigurable('view', TRUE);

$fields['alternate_tid'] = BaseFieldDefinition::create('entity_reference')
  ->setLabel(t('Chemical Family'))
  ->setCardinality(FieldStorageDefinitionInterface::CARDINALITY_UNLIMITED)
  ->setDescription(t('The family to which this chemical belongs.'))
  ->setSetting('target_type', 'taxonomy_term')
  ->setSetting('handler', 'default')
  ->setTranslatable(TRUE)
  ->setDisplayOptions('view', array(
    'label' => 'above',
    'type' => 'integer',
    'weight' => 0,
  ))
  ->setDisplayOptions('form', array(
    'type' => 'entity_reference_autocomplete',
    'weight' => 5,
    'settings' => array(
      'match_operator' => 'CONTAINS',
      'size' => '60',
      'autocomplete_type' => 'tags',
      'placeholder' => '',
    ),
  ))
  ->setDisplayConfigurable('form', TRUE)
  ->setDisplayConfigurable('view', TRUE);

return $fields;
  }

}

Answer 1

Probably because you have no preprocess hooks for your template? And did you define the templates with hook_theme()? You probably have render element => 'elements' there, but that means your output is actually in elements, not in content.

See https://www.drupal.org/node/2808481 for an issue to add generic entity templates to all entities with everything that's needed, that will also show you what you currently need to do yourself to get something in {{ content }}